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Even after nearly 3 years of loyal service, the Hubble Area Telescope continues to run and supply spectacular pictures of the universes. As one of NASA’s Excellent Observatories, its observations of far-off galaxies, exoplanets, and the growth of deep space have actually had an innovative influence on astronomy, astrophysics and cosmology. Hubble’s most current contribution can be found in the type of a deep-sky mosaic image that was built utilizing 16 years’ worth of observations. Called the “ Hubble Tradition Field“, this mosaic is being referred to as the biggest and most thorough “history book” of galaxies. All informed, it includes approximately 265,000 galaxies that go back to simply 500 million years after the Big Bang. Almost 7,500 specific direct exposures entered into the production of the Hubble Tradition Field, supplying a broad picture of the far-off Universe that recalls to the earliest noticeable times. In so doing, the image demonstrates how galaxies have actually altered with time, growing through mergers to end up being the huge galaxies we see in deep space today. This successfully suggests that 13.3 billion years of cosmic advancement have actually been narrated in this one image. This enthusiastic undertaking makes up the cumulative work of 31 Hubble programs by various groups of astronomers. It likewise included observations taken by numerous Hubble deep-field studies. These consist of the Hubble Deep Field in 1995, the Excellent Observatories Origins Deep Study(ITEM) of 2003, the Hubble Ultra Deep Field of 2004, and the eXtreme Deep Field(XDF) of 2012, which is the inmost view of deep space to date. As Garth Illingworth, Teacher Emeritus at UCSC and head of the group that put together the ” Now that we have actually gone broader than in previous studies, we are gathering much more far-off galaxies in the biggest such dataset ever produced. No image will exceed this one till future area telescopes like James Webb are released.” In addition to revealing galaxies in the noticeable light, the wavelength variety covers from the ultraviolet to the near-infrared part of the spectrum. This is type in modern-day astronomy and cosmology, because it enables crucial functions of galaxy assembly to be made evident. A fine example is ” Such elegant high-resolution measurements of the various galaxies in this brochure allow a broad swath of extragalactic research study,” stated brochure lead scientist Katherine Whitaker of the University of Connecticut, in Storrs. “Frequently, these sort of studies have actually yielded unexpected discoveries which have actually had the best influence on our understanding of galaxy advancement.” About a century back, Edwin Hubble (for whom the HST is called) explained galaxies are the “markers of area”. At the time, he was observing far-off galaxies and kept in mind how light originating from most of them was moved towards the red end of the spectrum– aka. “redshifted”, which is a sign that huge things are moving far from us. These observations verified a forecast made by Einstein’s Theory of General Relativity— that deep space was either in a state of growth or contraction. Subsequent studies have actually utilized galaxies to determine the rate of cosmic growth (referred to as the Hubble Continuous), which has actually likewise provided hints regarding the underlying physics of the universes, when chemical aspects stemmed, and how our Planetary system and life ultimately appeared. This broader view is particularly practical in that regard given that it includes about 30 times as lots of galaxies as the previous deep fields. The Tradition Field has actually likewise exposed numerous uncommon things, a number of which are the residues of crashes and mergers that occurred throughout the early Universe– what are described as galactic “train wrecks”. As you can picture, assembling this image was no simple job. As Dan Magee, of the University of California, Santa Cruz, the group’s information processing lead, described: ” Our objective was to put together all 16 years of direct exposures into a tradition image. Formerly, the majority of these direct exposures had actually not been created in a constant manner in which can be utilized by any scientist. Astronomers can pick the information in the Tradition Field they desire and deal with it right away, instead of needing to carry out a substantial quantity of information decrease prior to performing clinical analysis.” In Spite Of being the most in-depth and extensive picture of galaxies ever taken, this brand-new image is simply the very first in a series of Hubble Tradition Field images. The group is presently dealing with another set of images, which amount to more than 5,200 Hubble direct exposures, from another location of the sky. Looking ahead, astronomers wish to expand the multiwavelength variety in the tradition images to consist of a lot more information on This will consist of longer-wavelength IR and high-energy X-ray observations from 2 other NASA Great Observatories– the Spitzer Area Telescope and the Chandra X-ray Observatory. As staff member Rychard Bouwens of Leiden University in the Netherlands stated in ESA news release: ” One interesting element of these brand-new images is the a great deal of delicate color channels now readily available to see far-off galaxies, particularly in the ultraviolet part of the spectrum. With images at a lot of frequencies, we can dissect the light from galaxies into the contributions from old and young stars, along with active stellar nuclei.” In the meantime, no picture of deep space is anticipated to exceed the Hubble Tradition Field images one till next-generation area telescopes are released. These consist of the James Webb Area Telescope(JWST) and the Wide-Field Infrared Area Telescope(WFIRST), both of which have instruments will that use enhanced resolution and level of sensitivity over Hubble and hence allow more thorough studies. The large variety of galaxies in the Tradition Field image are likewise prime targets for future telescopes. As Illingworth stated in a HubbleSite news release: ” We have actually created this mosaic as a tool to be utilized by us and by other astronomers. The expectation is that this study will cause a a lot more meaningful, thorough and higher understanding of deep space’s advancement in the coming years … This will actually set the phase for NASA’s prepared Wide-Field Infrared Study Telescope (WFIRST). The Tradition Field is a pathfinder for WFIRST, which will record an image that is 100 times bigger than a normal Hubble picture. In simply 3 weeks’ worth of observations by WFIRST, astronomers will have the ability to put together a field that is much deeper and more than two times as big as the Hubble Tradition Field.” In addition, the JWST’s imaging abilities in the IR band (which are beyond the limitations of Hubble or Spitzer) will permit astronomers to penetrate much deeper into the Tradition Field image to expose more about how infant galaxies grew. The image(together with the specific direct exposures that entered into making it) is readily available through the Mikulski Archive for Area Telescopes(MAST).

These days, consumers can take their pick from an impressive array of fabulous items of diamond jewellery. For example, they can head online to select princess cut diamond engagement rings. All they need is a little spare time and a web connection. As long as they know where to look, they should be able to find the perfect princess cut diamond rings for them, and within their budgets too. Meanwhile, it seems as though the Earth is not the only planet in the Solar System to feature diamonds. According to a BBC report, these precious stones could be raining down on Saturn and Jupiter. Scientists in the US have calculated that there is an abundance of these items within the gas giants. The researchers noted that lightning storms within the planets’ atmospheres turn methane into carbon. This soot-like substance hardens as it falls into chunks of graphite and then into diamond. Eventually, these unusual ‘hail stones’ melt into a liquid at the core of the planets. Dr Kevin Baines from the University of Wisconsin-Madison and Nasa’s Jet Propulsion Laboratory suggested that the biggest diamonds would probably be around a centimetre in diameter. Expanding on this, he noted they would be “big enough to put on a ring, although of course they would be uncut”. The expert added: “The bottom line is that 1,000 tonnes of diamonds a year are being created on Saturn. People ask me – how can you really tell? Because there’s no way you can go and observe it. It all boils down to the chemistry. And we think we’re pretty certain.” Dr Baines stated that the process of diamond creation begins in the upper atmosphere or so-called ‘thunderstorm alleys’, where the soot forms. Explaining the subsequent processes, he said: “As the soot falls, the pressure on it increases. And after about 1,000 miles it turns to graphite – the sheet-like form of carbon you find in pencils.” By a depth of 6,000 kilometres, this graphite toughens into diamond. The specialist went on to draw attention to the “hellish” temperatures on Saturn and Jupiter. About this, he remarked: “Diamonds aren’t forever on Saturn and Jupiter. But they are on Uranus and Neptune, which are colder at their cores.” He presented his findings during the recent annual meeting of the Division for Planetary Sciences of the American Astronomical Society in the US along with his co-author, Mona Delitsky, from California Speciality Engineering. When asked to comment on the predictions, fellow expert Professor Raymond Jeanloz told the BBC: “The idea that there is a depth range within the atmospheres of Jupiter and (even more so) Saturn within which carbon would be stable as diamond does seem sensible.” He added: “Given the large sizes of these planets, the amount of carbon (therefore diamond) that may be present is hardly negligible.” Of course, consumers do not have to go to the lengths of trying to source precious stones in space. When they are after a princess cut engagement ring or other similar item, they can simply turn to the web and place their orders. About the Author – Anna Longdin is a regular contributor to lifestyle blogs and loves perusing the fabulous range of jewellery products now available. Find out where she gets her inspiration by visiting Marlow’s Diamonds.

In addition to James K's answer, many gases exist in the disk of material that forms into planets. What's a gas as opposed to a liquid or solid also depends on temperature and pressure. The most abundant "gases" in our solar-system are hydrogen, helium, CO2, H2O, CH4, NH3, N2, O2, CO, Neon (and maybe some others I've overlooked), in something sort of close to that order. Many of these "gases" are also ices that form up the majority of comets. During planetary formation, the ring of debris is too warm for hydrogen, Helium and Neon to be anything but a gas, though some hydrogen is bound to heavier elements and abundant in planet formation. Helium and Neon and the other Noble Gases don't bind well with other elements. The other abundant "gases", H20, CO2, NH3, CH4, etc, can exist as ices past their respective frost lines. That's why those molecular compounds are much more common in the outer part of the solar system. Earth and Mars formed inside the frost-line so they formed mostly out of rocky material, after which, much of the lighter elements, primarily gases and liquids, were acquired by comet impacts after formation, though some probably existed prior too formation. During the late heavy bombardment there were many large impacts and one consequence of very large comet or meteor impacts is a rise in temperature, so, even in the early solar-system when the sun wasn't as luminous as it is now, the planets, Earth and Mars spent some of the time quite hot. There's two primary ways a planet can lose it's atmosphere, Jeans Escape and by the solar wind. The solar wind is made up of almost entirely charged particles, so if a planet has a magnetic field, the impact of those high speed particles is largely deflected, where as, if they impact the upper atmosphere, the planet can lose it's atmosphere like tiny billiard balls being knocked off one at a time. While the method of those two ways a planet can lose it's atmosphere are different, it comes down to basically the same thing. When gas molecules on the outer edge of a planet's atmosphere move faster than escape velocity they are likely to escape the planet into space and because lighter gas molecules move faster than heavier ones. That's the Maxwell-Boltzmann law or Root-mean-square formula, planets are more likely to retain heavier gases. Venus and Mars have both lose most of their lighter gases, H20, CH4, NH3 but CO2 is heavy enough to have been retained by both those planets, though it's worth pointing out that we don't know how much CO2 Mars had millions and billions of years ago. Mars may have lost much of it's CO2 over time as well. It just lost it more slowly than the lighter gases. Mars was able to retain some of it's water, however, in the form of ice. Venus, like Mars, lost nearly all of it's gaseous water. We know that Venus used to have much more water because it's very high D to H ratio wouldn't be possible unless it had lost a significant percentage of it's water, likely 99.9% or higher. Earth is massive enough and Earth has a strong magnetic field, so Earth is able to retain it's lighter gases like CH4, NH3 and atmospheric H20, though Earth loses Hydrogen and Helium to space. NH3 is kind of interesting because it dissolves in water quite readily, so as soon as the young Earth had oceans, those oceans were likely Ammonia/water with whatever else readily dissolved in the liquid such as Iron. The early oceans are thought to have been brown colored from the dissolved Iron. But Earth's young atmosphere was likely mostly CO2 and CH4 with most of the H20 in liquid form, (and at times, much of it was ice). As life and photosynthesis began releasing Oxygen, Oxygen readily bonded with the CH4 and dissolved Iron in the oceans, turning the oceans blue and in time, making the Atmosphere free of CH4 and more abundant with O2. It's unclear (and perhaps unlikely?) if Mars and Venus ever underwent that Oxygenation period that Earth did. Having abundant liquid oceans and having photosynthetic life made a significant difference to Earth's atmosphere. You mentioned plate tectonics and that plays a role too as does the chemistry that happens in the oceans and below the surface of a planet. The main reason Mars is 95% CO2 now is because it's small and it doesn't have a good magnetic field, only small localized ones. It lost most of it's atmosphere and nearly all of it's lighter gas molecules.

Crescent ♉ Taurus Moon phase on 3 June 2035 Sunday is Waning Crescent, 26 days old Moon is in Taurus.Share this page: twitter facebook linkedin Previous main lunar phase is the Last Quarter before 4 days on 30 May 2035 at 07:31. Moon rises after midnight to early morning and sets in the afternoon. It is visible in the early morning low to the east. Moon is passing about ∠6° of ♉ Taurus tropical zodiac sector. Lunar disc appears visually 2.5% wider than solar disc. Moon and Sun apparent angular diameters are ∠1939" and ∠1891". Next Full Moon is the Strawberry Moon of June 2035 after 17 days on 20 June 2035 at 19:37. There is low ocean tide on this date. Sun and Moon gravitational forces are not aligned, but meet at big angle, so their combined tidal force is weak. The Moon is 26 days old. Earth's natural satellite is moving from the second to the final part of current synodic month. This is lunation 437 of Meeus index or 1390 from Brown series. Length of current 437 lunation is 29 days, 7 hours and 17 minutes. It is 38 minutes longer than next lunation 438 length. Length of current synodic month is 5 hours and 27 minutes shorter than the mean length of synodic month, but it is still 42 minutes longer, compared to 21st century shortest. This lunation true anomaly is ∠338.4°. At the beginning of next synodic month true anomaly will be ∠354.2°. The length of upcoming synodic months will keep decreasing since the true anomaly gets closer to the value of New Moon at point of perigee (∠0° or ∠360°). 10 days after point of apogee on 24 May 2035 at 09:19 in ♐ Sagittarius. The lunar orbit is getting closer, while the Moon is moving inward the Earth. It will keep this direction for the next 2 days, until it get to the point of next perigee on 6 June 2035 at 11:36 in ♊ Gemini. Moon is 369 741 km (229 746 mi) away from Earth on this date. Moon moves closer next 2 days until perigee, when Earth-Moon distance will reach 357 357 km (222 051 mi). 4 days after its descending node on 30 May 2035 at 10:00 in ♓ Pisces, the Moon is following the southern part of its orbit for the next 8 days, until it will cross the ecliptic from South to North in ascending node on 11 June 2035 at 20:42 in ♍ Virgo. 18 days after beginning of current draconic month in ♍ Virgo, the Moon is moving from the second to the final part of it. 9 days after previous South standstill on 25 May 2035 at 00:53 in ♑ Capricorn, when Moon has reached southern declination of ∠-18.782°. Next 3 days the lunar orbit moves northward to face North declination of ∠18.820° in the next northern standstill on 7 June 2035 at 10:40 in ♋ Cancer. After 2 days on 6 June 2035 at 03:21 in ♊ Gemini, the Moon will be in New Moon geocentric conjunction with the Sun and this alignment forms next Sun-Moon-Earth syzygy.

NASA's two Voyager spacecraft show nothing's simple at the edges of the solar system. After a three-decade journey away from Earth, the two Voyager spacecraft are approaching the outer edges of the solar system. To scientists' surprise, the satellites have revealed a region vastly different than previously modeled. The solar system's boundary is defined by a steady stream of particles known as the solar wind. The solar wind shoots out from the sun until it pushes up against the galactic medium and slows down at a line called the termination shock. Beyond this lies the heliosheath, where the solar wind's journey stops completely. Scientists thought the solar wind turned back smoothly at this point, sweeping back around the outskirts of the solar system. As seen in the video below, Voyager now shows that solar wind hits the heliosheath and piles up into a frothy layer filled with magnetic bubbles. This layer must have an affect on how intense energetic particles from the rest of the universe, called cosmic rays, make it into our solar system. But scientists have yet to figure out if the bubbles help stop the bulk of the rays, or are the prime factor that allows them to enter.

(Inside Science) -- Terrestrial animals may owe a special debt to the sun and the moon. It may have been their combined pull on ancient Earth's oceans that helped primitive air-breathing fish gain a toehold on land, new research suggests. In a new study, published in the journal Proceedings of the Royal Society A, physicist Steven Balbus argues that the gravitational forces generated by the sun and moon would have been conducive to the formation of a vast network of isolated tidal pools during the Devonian Period, between 420 to 360 million years ago, when fish-like vertebrates first clambered out of the sea. "By the end of the Devonian, there were vertebrates that were quite at home moving around on land," said Balbus, who is at the University of Oxford in the United Kingdom. According to Balbus, a rather remarkable confluence of cosmic, geological and biological events occurred during the Devonian period that helped jump-start life on land. First, when viewed from the Earth, the sun and the moon appeared to be almost the same size, as is true today. This is called having the same angular diameter. "The sun is much bigger than the moon, but it's also much farther away, so the two bodies look to be about the same size to us. This is extraordinary," Balbus said. He added that it's very unusual for an Earth-sized planet to have such a large moon. One consequence of this arrangement is that the "tidal force" of the sun and the moon on our planet are similar. The tidal force is a side effect of the force of gravity and is responsible for ocean tides. Because the Earth is a sphere, gravity doesn't act equally on all parts of it. "The part of the surface that's closer to the sun is pulled a little bit more strongly, and the part that's farther away is pulled a little less strongly," said Balbus. "The same thing happens with the moon." Because the tidal forces of the sun and moon are similar, the timing and size of Earth's ocean tides can change depending on whether the solar and lunar tidal forces are opposed to one another or acting in synchrony. The variety of ocean tide patterns generated by the sun and the moon would have been especially noticeable during the Devonian due to the arrangement of our Earth's continents, Balbus said. "The positions of Earth’s continents have changed over time because of [plate tectonics]. They had a rather special orientation in the Devonian," explained Balbus. Watery safe havens Specifically, there were only two "supercontinents," Gondwana and Euramerica, at the time, and the two land masses were separated by an expanse of water known as the Rheic Ocean. The Rheic Ocean had a unique tapered shape, so that its eastern side was narrower and shallower than its western end, which would be conducive to the formation of large tides. "This would have helped create a very extensive and very complex network of inland tidal pools," Balbus said. The final part of Balbus' proposal is biological. The Devonian period also happened to be when scientists think stubby-legged fish with primitive air-breathing lungs known as tetrapods first ventured onto land. If strong tides stranded animals in shallow pools, they could be trapped and perish if unable to scramble to larger bodies of water. If, as Balbus suggests, tidal pools were plentiful during the Devonian, early tetrapods that were mobile would have had an easier time surviving out of the water because they could have dipped back into one of the many refuges scattered across the landscape. From there, it would have been a relatively short leap to a full-time terrestrial lifestyle, Balbus said. A bold idea Per Alhberg, an evolutionary biologist at Uppsala University in Sweden, praised Balbus's original thinking. "I love the boldness of this paper ... and the way Steven has dared to link together wildly different scientific disciplines in an attempt to understand a unique evolutionary event," said Alhberg, who was not involved in the study. Alhberg also thinks the scenario envisioned by Balbus is very plausible. "There is direct evidence that many of the earliest tetrapods and their fish ancestors lived in deltaic or marginal marine environments, so one way or another they must have passed through the tidal zone on the way from water to land," Alhberg said. "It could hardly have failed to have an effect on them, and we know that there are plenty of animals today that exploit the intertidal environment and live partly in, partly out of, the water." Balbus said that developing his theory has made him skeptical of the notion that complex terrestrial life might be common in the universe. "A lot of things had to come together in a strange way on the Earth," he added. Alhberg, on the other hand, thinks alien life could still be plentiful, but that its makeup might be different from Earth's. "An Earth-like planet without a moon might have a rich diversity of life in the oceans but rather simple microorganism-dominated ecosystems on land," he said. Ker Than is a freelance writer living in the Bay Area. He tweets at @kerthan.

By Sam Wilkinson There are a couple of man-made objects in space that almost everyone will know about: the International Space Station, the Hubble Space Telescope, Mars Science Laboratory Curiosity and maybe Voyager I and/or II. However, there is so much other man-made stuff in space it’s crazy (and it’s actually starting to become a problem). This abundance of space-faring objects can make it hard for some truly awesome experiments, missions etc to get much exposure! I’d like to fix that with a recurring blog post series called “Awesome Stuff in Space”. Since this is the inaugural post, I’m going to cover two of the coolest lesser-known things currently in space (in my humble opinion), as well as an awesome example of recycling (which is no longer in space). 1. LAGEOS: The (really useful) orbital disco ball When asked what the most precise method currently available for determining the position of a place on earth was, my first response would probably be military-grade GPS, but I’d be wrong. In fact, the most precise way to determine your position on earth is by bouncing a laser beam off of what is essentially a disco ball in space. That disco ball would either be LAGEOS-1 or LAGEOS-2 (LAser GEOdynamics Satellite), two 60cm wide spheres each covered in 426 retroreflectors (a special mirror that reflects light back the way it came) currently orbiting the earth at 5,900km above us. By measuring the time taken for a laser pulse to travel to a LAGEOS satellite and back, the distance between the ground station and the satellite can be calculated to a very high degree of accuracy (~1 inch for thousands of miles). Since the orbits of the LAGEOS satellites are very stable, their positions can be determined to a high degree of accuracy. This coupled with the distance between the ground station and the satellite can be used to determine the precise location of the ground station. There are ground stations performing these measurements in many countries, and the results are used to study tectonic plate movement by groups from around the world. 2. Dawn: Exploring new frontiers in new ways One of my favourite statistics on the solar system is this: approximately 42% of the mass of the asteroid belt is made up from just two objects, the dwarf planet Ceres and the asteroid Vesta. These also happen to be the two main objectives for the spacecraft Dawn, launched in September of 2007. Dawn has already travelled to Vesta, and is currently en route to Ceres. The study of Ceres and Vesta will greatly contribute to our understanding of the formation of planets. Since Ceres and Vesta are the two largest remaining protoplanets (planetary embryos) in the solar system, the observation of these objects will give us a peek at the earliest stages in the formation of the solar system. What makes Dawn even more special, aside from it being the first craft to travel to both Vesta and Ceres (hopefully), is that it is NASA’s first purely exploratory mission to use ion thrusters as its sole mode of propulsion. 3. SuitSat-1: “A Russian Brainstorm” The concept behind SuitSat-1 is quite simple, put some simple electronics (radio communications system, telemetry) into a Russian Orlan spacesuit, then throw it out of the airlock. According to Frank Bauer of NASA’s Goddard Space Flight Center, “SuitSat is a Russian brainstorm, some of our Russian partners in the ISS program … had an idea: Maybe we can turn old spacesuits into useful satellites.” Aside from broadcasting voice messages from students around the world, and some telemetry data, SuitSat-1 also looked really eerie. Images of Suit-Sat as it was being jettisoned from the ISS are kind of haunting… -See Part II of Amazing Stuff in Space here…

The Dark Side of the Universe by Jan Smit and Renske Smit To put us, as book reviewers, in context, like many scientists, we study our surroundings in an effort to understand where we came from. Jan, the historical geologist, likes to begin with the birth of our solar system 4.56 billion years ago. Before that, in his mind, there was nothing. Renske, the astrophysicist, works on much larger time scales, beginning with the birth of the earliest galaxies 13.2 billion years ago. For her, our solar system is just a little speck in recent history. It is therefore rare to come across a publication that piques the interest of both of us. Such was the case with particle physicist Lisa Randall’s new book,/Dark Matter and the Dinosaurs./ The first thought that crossed both our minds when reading the title of this book was: “Oh, no, not again, another outlandish proposal for the extinction of dinosaurs….” However, we were relieved to find that, right from the start, Randall dismisses almost all connections between dark matter and the mass-extinction event that wiped out the dinosaurs. Instead, the book takes the reader on a journey through the cosmos, describing what we know about dark matter and what more we are poised to learn as new and better equipment becomes available. Randall starts with an outline of “The Big Questions”: Why is there something rather than nothing? What happened during the Big Bang? What came before the Big Bang? She explains that there has to be dark matter because the behavior of merged galaxy clusters like the Bullet Cluster cannot be explained otherwise. She skims through the Big Bang, cosmic inflation, and how the galaxies formed when normal matter hitchhiked along with dark matter to form the seeds of the first stars. Without dark matter, we learn, our Milky Way and Earth as we know it would not exist. Having covered the creation of stars, the book turns to our solar system. Here, Randall vividly describes the comets and asteroids that have hit or will hit Earth. She recounts how meteorites may have brought essential amino acids and perhaps some water to Earth and describes the Chicxulub asteroid/comet and its role in the mass extinction at the end of the Cretaceous. The story of the Chicxulub impact and its role in the extinction of the dinosaurs is highly entertaining and largely correct. In the last chapters of the book, Randall outlines an important new way of thinking that applies to the search for viable dark matter models. The only way to find out whether something is allowed or even preferred is to evaluate the consequences of new assumptions and determine their experimental implications. Although observations indicate that dark matter consists of a mostly noninteracting substance, no experiment can currently rule out that dark matter may have a weak interaction with its own particles or, alternatively, that a small fraction of particles of dark matter have a moderately large interaction with one another. If true, these new models would be an extension of current theories, some of which can be tested in new experiments over the next few years. One model explored in this book shows how a narrow disk of dark matter in the galactic plane could potentially explain the periodicity in the crater records on Earth and could have contributed to the impact 66 million years ago that generated the mass extinction of the dinosaurs. Randall is quick to admit that the data that favor such a model are still tenuous and that the theory requires further testing. So does that mean that dark matter and dinosaurs are connected? Likely not, although there is a chance that they could be. In the end, drawing a definitive connection between the two is not really the aim of the book. Randall has a manner of writing that is pleasant and compelling: Cliff-hangers at the end of each chapter reel you into the next. Her method of using everyday situations as metaphors for explaining complicated concepts in physics is also very effective. For example, she describes how scientists know that dark matter is present in much the same way that you may be able to infer that George Clooney is in busy downtown New York: You may not see, smell, or hear him, but you can observe that all faces on the street are directed toward him. Despite the provocative title, the scientific reasoning set out in this book is sound and interesting. Randall succeeds in guiding the reader through the history of the cosmos and the Earth from the Big Bang to the emergence of life as we know it in a fun and captivating way. The rich metaphors and personal anecdotes peppered throughout the book make this a very enjoyable read for both lay readers and scientists of various backgrounds.

I am looking for basic data regarding red-shifting that comes with reliable measure of distance of the emitting star. Red shift is usually measured for galaxies rather than individual stars. Unless a star has just gone supernova, it's usually not bright enough to be seen even w the world's most powerful telescopes at the distances where cosmological redshift comes into play. Hubble's law operates over large distances; the expansion constant being 67.8 km/sec per megaparsec (3.3 million light years) Andomeda galaxy (M31) is 2.54 million light years away, and although some individual stars are visible at that distance, the galaxy has a net blueshift of 0.001001 (303 km/sec) due to its peculiar (i.e. non-Hubble) velocity. Further out is where you start to see redshifts in excess of peculiar motion; and there you need to start using standard candles of some sort. Cepheid variables when visible, Supernova, globular cluster brightness functions, are all used, as well as some spectral methods: Cosmic distance ladder Supernova measurements go the furthest out, highest redshift, but are still a bit of a can of worms as far as interpretation goes.

Behold: Arp 273 – a great interstellar battle featuring upper galaxy UGC 1810 and its smaller collisional neighbour UGC 1813. War is hell. To wit: The overall shape of the UGC 1810 — in particular its blue outer ring — is likely a result of wild and violent gravitational interactions. The blue colour of the outer ring at the top is caused by massive stars that are blue hot and have formed only in the past few million years. The inner part of the upper galaxy — itself an older spiral galaxy — appears redder and threaded with cool filamentary dust. A few bright stars appear well in the foreground, unrelated to colliding galaxies, while several far-distant galaxies are visible in the background. Arp 273 lies about 300 million light years away toward the constellation of Andromeda. Quite likely, UGC 1810 will devour its galactic sidekicks over the next billion years and settle into a classic spiral form.

This image illustrates the four common states of matter: solid, liquid, gas, and plasma. States of Matter This figure shows the four common states of matter: solid, liquid, gas, and plasma. Consider water as an example. Solid water is ice. Liquid water is, well, water. We call water in its gaseous form "water vapor". A plasma created from water would include electrons, protons (hydrogen atom nuclei), and oxygen atom nuclei (protons and neutrons). There are special names for most transitions from one state to another. Freezing is turning from a liquid to a solid; melting is turning from a solid to a liquid. The transition from liquid to gas can happen by boiling or evaporation. Condensation is changing from a gas to a liquid. Sometimes (usually at low pressure) a solid can become a gas directly (without first melting to become a liquid); this transformation is called "sublimation". Removing electrons from atoms (usually in a gas) to produce a plasma is called "ionization". Stars are made of plasma, so plasma is the most abundant form of matter in the There are several other very exotic and unusual forms of matter that we don't encounter in daily life. A Bose-Einstein condensate can only form at temperature near absolute zero, and was first created in a lab in 1995. Degenerate matter can come into being under incredibly high pressure inside white dwarf and neutron stars. There are other very strange, very rare forms of matter as well. You might also be interested in: Solid is one of the four common states of matter. The three others are gas, liquid, and plasma. There are also some other exotic states of matter that have been discovered in recent years. Unlike liquids...more Plasma is known as the fourth state of matter (the first three states being solid, liquid and gas).Matter in ordinary conditions on Earth has electrons that orbit around the atomic nucleus. The electrons...more The cryosphere includes the parts of the Earth system where water is in its frozen (solid) form. This includes snow, sea ice, icebergs, ice shelves, glaciers, ice sheets, and permafrost soils. Approximately...more Oxygen is a chemical element with an atomic number of 8 (it has eight protons in its nucleus). Oxygen forms a chemical compound (O2) of two atoms which is a colorless gas at normal temperatures and pressures....more Any substance, called matter, can exist as a solid material, liquid, or gas. These three different forms are called states. Matter can change its state when heated. As a solid, matter has a fixed volume...more One process which transfers water from the ground back to the atmosphere is evaporation. Evaporation is when water passes from a liquid phase to a gas phase. Rates of evaporation of water depend on factors...more White Dwarfs are the remnants of stars that were massive enough to stay alive using nuclear fusion in their cores, but not massive enough to blow apart in a Type II supernova. When stars like our own sun...more

DIALLING, sometimes called gnomonics, is a branch of applied mathematics which treats of the construction of sun-dials, that is, of those instruments, either fixed or portable, which determine the divisions of the day by the motion of the shadow of some object on which the sun's rays fall. It must have been one of the earliest applications of a knowledge of the apparent motion of the sun ; though for a long time men would probably be satisfied with the division into morning and afternoon as marked by sun-rise, sun-set, and the greatest elevation. History.The earliest mention of a sun-dial is found in Isaiah xxxviii. 8 : " Behold, I will bring again the shadow of the degrees which is gone down in the sun-dial of Ahaz ten degrees backward." The date of this would be about 700 years before the Christian era, but we know nothing of the character or construction of the instrument. The earliest of all sun dials of which we have any certain knowledge was the hemicycle, or hemisphere, of the Chal-dean astronomer Berosus, who probably lived about 340 B.C. It consisted of a hollow hemisphere placed with its rim perfectly horizontal, and having a bead, or globule, fixed in any way at the centre. So long as the sun remained above the horizon the shadow of the bead would fall on the inside of the hemisphere, and the path of the shadow during the day would be approximately a circular arc. This arc, divided into twelve equal parts, deter-mined twelve equal intervals of time for that day. Now, supposing this were done at the time of the solstices and equinoxes, and on as many intermediate days as might be considered sufficient, and then curve lines drawn through the corresponding points of division of the different arcs, the shadow of the bead falling on one of these curve lines would mark a division of time for that day, and thus we should have a sun-dial which would divide each period of daylight into twelve equal parts. These equal parts were called temporary hours; and, since the duration of daylight varies from clay to day, the temporary hours of one day would differ from those of another ; but this inequality would probably be disregarded at that time, and especially in countries where the variation between the longest summer day and the shortest winter day is much less than in our climates. The dial of Berosus remained in use for centuries. The Arabians, as appears from the work of Albateguius, still followed the same construction about the year 900 A.D. Four of these dials have in modern times been found in Italy, One, discovered at Tivoli in 1746, is supposed to have belonged to Cicero, who, in one of his letters, says that he had sent a dial of this kind to his villa near Tusculum. The second and third were found in 1751 one at Castel-Nuovo, and the other at Bignauo; and a fourth was found in 1762 at Pompeii. G. H. Martini, the author of a dissertation in German on the dials of the ancients, says that this dial was made for the latitude of Memphis ; it may therefore be the work of Egyptians, per-haps constructed in the school of Alexandria. It is curious that no sun-dial has been found among the antiquities of Egypt, and their sculptures give no indication of any having existed. It has, however, been supposed that the numerous obelisks found everywhere were erected in honour of the sun and employed as gnomons. Herodotus has recorded that the Greeks derived from the Babylonians the use of the gnomon, but the great pro-gress made by the Greeks in geometry enabled them in later times to construct dials of great complexity, some of which remain to us, and are proofs, not only of extensive knowledge, but also of great ingenuity. Ptolemy's Syntaxis treats of the construction of dials by means of his analemma, an instrument which solved a variety of astronomical problems. The constructions given by him were sufficient for regular dials, that is, horizontal dials, or vertical dials facing east, west, north, or south, and these are the only ones he treats of. It is certain, however, that the ancients were able to construct declining dials, as is shown by that most interesting monument of ancient gnomonicsthe Tower of the Windswhich is still in existence at Athens. This is a regular octagon, on the faces of which the eight principal winds are represented, and over them eight different dialsfour facing the cardinal points and the other four facing the intermediate directions. The date of the dials is long subsequent to that of the tower ; for Vitruvius, who describes the tower in the sixth chapter of his first book, says nothing about the dials, and as he has described all the dials known in his time, we must believe that the dials of the tower did not then exist. The tower and its dials are described by Stuart in his Antiquities of Athens. The hours are still the temporary hours, or, as the Greeks called them, hectemoria. As already stated, the learning and ingenuity of the Greeks enabled them to construct dials of various forms among others, dials of suspension intended for travellers; but these are only spoken of and not explained; they may have been like our ring-dials. The Romans were neither geometers nor astronomers, and the science of gnomonics did not flourish among them. The first sun-dial erected at Rome was in the year 290 B.C, and this Papirius Cursor had taken from the Samnites. A dial which Valerius Messala had brought from Catania, the latitude of which is five degrees less than that of Borne, was placed in the forum in the year 261 B.C. The first dial actually constructed at Borne was in the year 164 B.C., by order of Q. Marcius Philippus, but, as no other Roman has written on gnomonics, this was perhaps the work of a foreign artist. If, too, we remember that the dial found at Pompeii was made for the latitude of Mem-phis, and consequently less adapted to its position than that of Catania to Rome, we may infer that mathematical knowledge was not cultivated in Italy. The Arabians were much more successful. They attached great importance to gnomonics, the principles of which they had learned from the Greeks, but they greatly simplified and diversified the Greek constructions. One of their writers, Abul-Hassan, who lived about the beginning of the 13th century, taught them how to trace dials on cylindrical, conical, and other surfaces. He even introduced equal or equinoctial hours, but the idea was not sup-ported, and the temporary hours alone continued in use. Where or when the great and important step already conceived by Abul-Hassan, and perhaps by others, of reckoning by equal hours was generally adopted cannot now be determined. The history of gnomonics from the 13th to the beginning of the 16th century is almost a blank, and during that time the change took place. We can see, however, that the change would necessarily follow the introduction of clocks and other mechanical methods of measuring time ; for, however imperfect these were, the hours they marked would be of the same length in summer and in winter, and the discrepancy between these equal hours and the temporary hours of the sun-dial would soon be too important to be overlooked. Now, we know that a balance clock was put up in the palace of Charles V. of France about the year 1370, and wo may reasonably sup-pose that the new sun-diafs came into general use during the 14th and 15th centuries. Among the earliest of the modern writers on gnomonics must be named Sebastian Munster, a cordelier who pub-lished his Horologiographia&t Basel in 1531. He gives a number of correct rules, but without demonstrations. Among his inventions was a moon-dial, but this does not admit of much accuracy. During the 17th century dialling was discussed at great length by all writers ou astronomy. Clavius devotes a quarto volume of 800 pages entirely to the subject. This was published in 1612, and may be considered to contain all that was known at that time. In the 18th century clocks and watches began to supersede sun-dials, and these have gradually fallen into disuse except as an additional ornament to a garden, or in remote country districts where the old dial on the church tower still serves as an occasional check on the modern clock by its side. The art of constructing dials may now be looked upon as little more than a mathematical recrea-tion. General Principles.The diurnal and the annual motions of the earth are the elementary astronomical facts on which dialling is founded. That the earth turns upon its axis uniformly from west to east in 24 hours, and that it is carried round the sun in one year at a nearly uniform rate, is, we know, the correct way of expressing these facts. But the effect will be precisely the same, and it will suit our purpose better, and make our explanations easier, if we adopt the ideas of the ancients, of which our senses furnish apparent confirmation, and assume the earth to be fixed. Then, the sun and stars revolve round the earth's axis uniformly from east to west once a day,the sun lagging a little behind the stars, making its day some 4 minutes longer, so that at the end of the year it finds itself again in the same place, having made a complete revolution of the heavens relatively to the stars from west to east. The fixed axis about which all these bodies revolve daily is a line through the earth's centre ; but the radius of the earth is so small, compared with the enormous distance of the sun, that, if we draw a parallel axis through any point of the earth's surface, we may safely look on that as being the axis of the celestial motions. The error in the case of the sun would not, at its maximum, that is, at 6 A.M. and 6 P.M., exceed half a second of time, and at noon would vanish. An axis so drawn is in the plane of the meridian, and points, as we know, to the pole,its elevation being equal to the latitude of the place. The diurnal motion of the stars is strictly uniform, and so would that of the sun be if the daily retardation of about 4 minutes, spoken of above, were always the same. But this is constantly altering, so that the time, as measured by the sun's motion, and also consequently as measured by a sun-dial, does not move on at a strictly uniform pace. This irregularity, which is slight, would be of little consequence in the ordinary affairs of life, but clocks and watches being mechanical measures of time could not, except by extreme complication, be made to follow this irregularity, even if desirable, which is not the case. The clock is constructed to mark uniform time in such wise that the length of the clock day shall be the average of all the solar days in the year. Four times a year the clock and the sun-dial agree exactly ; but the sun-dial, now going a little slower, now a little faster, will be some-times behind, sometimes before the clockthe greatest accumulated difference being about 16 minutes for a few days in November, but on the average much less. The four days on which the two agree are April 15, June 15, September 1, and December 24. Clock-time is called mean time, that marked by the sun-dial is called apparent time, and the difference between them is the equation of time. It is given in most calendars and almanacs, frequently under the heading " clock slow,'-" clock fast." When the time by the sun-dial is known, the equation of time will at once enable us to obtain the corresponding clock time, or vice versa. Atmospheric refraction introduces another error, by altering the apparent position of the sun ; but the effect is too small to need consideration in the construction of an instrument which, with the best workmanship, does not after all admit of very great accuracy. The general principles of dialling will now be readily understood. The problem before us is the following : A rod, or style, as it is called, being firmly fixed in a direction parallel to the earth's axis, we have to find how and where points or lines of reference must be traced on some fixed surface behind the style, so that when the shadow of the style falls on a certain one of these lines we may know that at that moment it is solar noon,that is, that the plane through the style and through the sun then coincides with the meridian ; again, that when the shadow reaches the next line of reference, it is 1 o'clock by solar time, or, which comes to the same thing, that the above plane through the style and through the sun has just turned through the twenty-fourth part of a complete revolution; and so on for the subsequent hours,the hours before noon being indi-cated in a similar manner. The style and the surface on which these lines are traced together constitute the dial. The position of an intended sun-dial having been selected whether on church tower, south front of farm-stead, or garden wallthe surface must be prepared, if necessary, to receive the hour-lines. The chief, and in fact the only practical difficulty will be the accurate fixing of the style, for on its accuracy the value of the instrument depends. It must be in the meridian plane, and must make an angle with the horizon equal to the latitude of the place. The latter condition will offer no difficulty, but the exact determination of the meridian plane which passes through the point where the style is fixed to the surface is not so simple. We shall, further on, show how this may be done; and, in the meantime, we shall assume that we have found the true position, and have firmly fixed the style to the dial and secured it there by cross wires, or by other means. The style itself will be usually a strong metal wire whose thickness may vary with circumstances; and when we speak of the shadow cast by the style it must always be understood that the middle line of the thin band of shade is meant. The point where the style meets the dial is called the centre of the dial. It is the centre from which all the hour-lines radiate. The position of the xii o'clock line is the most important to determine accurately, since all the others are usually made to depend on this one. We cannot trace it correctly on the dial until the style has been itself accurately fixed in its proper place, as will be explained hereafter. When that is done the xn o'clock line will be found by the inter-section of the dial surface with the vertical plane which contains the style ; and the most simple way of drawing it on the dial will be by suspending a plummet from some point of the style whence it may hang freely, and waiting until the shadows of both style and plumb line coincide on the dial. This single shadow will be the xn o'clock line. In one class of dials, namely, all the vertical ones, the xn o'clock line is simply the vertical line from the centre; it can, therefore, at once be traced on the dial face by using a fine plumb line. The xn O'CIOCK line being traced, the easiest and most accurate method of tracing the other hour lines would at the present day when good watches are common, be by marking where the shadow of the style falls when 1, 2, 3, &c, hours have elapsed since noon, and the next morning by the same means the forenoon hour lines could be traced ; and in the same manner the hours might be subdivided into halves and quarters, or even into minutes. But formerly, when watches were not, the tracing of the i, II, in, &c. o'clock lines was done by calculating the angle which each of these lines would make with the xn o'clock line. Now, except in the simple cases of a horizontal dial or of a vertical dial facing a cardinal point, this would require long and intricate calculations, or elabor-ate geometrical constructions, implying considerable mathematical knowledge, but also introducing increased chances of error. The chief source of error would lie in the uncer-tainty of the data ; for the position of the dial-plane would have to be found before the calculations began, that is, it would be necessary to know exactly by how many degrees it declined from the south towards the east or west, and by how many degrees it inclined from the vertical. The ancients, with the means at their disposal, could obtain these results only very roughly. Dials received different names according to their posi-tion : Horizontal dials, when traced on a horizontal plane ; Vertical dials, when on a vertical plane facing one of the cardinal points; Vertical declining dials, on a vertical plane not facing a cardinal point; Inclining dials, when traced on planes neithei vertical nor horizontal (these were further distinguished as reclin-ing when leaning backwards from an observer, proclining when leaning forwards); Eqidnoctial dials, when the plane is at right angles to the earth's axis, &c. &c. We shall limit ourselves to an investigation of the simplest and most usual of these cases, referring the reader, for further details, to the later works given at the end of this article. Dial Construction.A very correct view of the problem of dial construction may be obtained as follows : Conceive a transparent cylinder (fig. 1) having an axis AB parallel to the axis of the earth. On the surface of the cylinder let equidistant generating lines be traced 15° apart, one of them xn.. xn being in the meridian plane through AB, and the others I... I, n...n, &c, following in the order of the sun's motion. Then the shadow of the line AB will obviously fall on the line £11...XII at apparent noon, on the line I...I at one hour afternoon, on II...II at two hours after noon, and so on. If now the cylinder be cut by any plane MN representing the plane on which the dial is to be traced, the shadow of AB will be intercepted by this plane, and fall on the lines Axu, Ai, An, &c. The construction of the dial consists in determining the angles made by Ai, An, &c. with Axn; the line Axn itself, being in the vertical plane through AB, may be supposed known. For the purposes of actual calculation, perhaps a trans-parent sphere will, with advantage, replace the cylinder, and we shall here apply it to calculate the angles made by the hour line with the xn o'clock line in the two cases of a horizontal dial and of a vertical south dial. Horizontal Dial.Let PEy (fig. 2), the axis of the supposed transparent sphere, be directed towards the north and south poles of the heavens. Draw the two great circles, HMA, QMa, the former horizontal, the other perpendicular to the axis Vp, and therefore coinciding with the plane of the equator. Let EZ he vertical, then the circle QZP will be the meridian, and by its intersection A with the horizontal will determine the xn o'clock line EA. Next divide the equatorial circle QMa into 24 equal parts ai, be, cd, &c. ... of 15° each, beginning from the meridian Pa, and through the various points of division and the poles draw the great circles Fbp, Fcp, &c. . . . These will exactly correspond to the equidistant generating lines on the cylinder in the previous construction, and the shadow of the style will fall on these circles after successive intervals of 1, 2, 3, &c. hours from noon. If they meet the horizontal in the points B, C, D, &c, then EB, EC, ED, &c. . . . will be the i, II, in, &c., hour lines required ; and the problem of the horizontal dial consists in calculating the angles which these lines make with the xn o'clock line EA, whose position is known. The spherical triangles PAB, PAC, &c, enable us to do this readily. They are all right-angled at A, the side PA is the latitude of the place, and the angles APB, APC, &c, are respectively 15°, 30°, &c, then tan. AB = tan. 15° sin. latitude, tan. AC = tan. 30° sin. latitude, These determine the sides AB, AC, &c. that is, the angles AEB, AEC, &c, required. For examples, let us find the angles made by the I o'clock line at the following placesMadras, London, Edinburgh, and Hammer" fest (Norway). == TABLE == Thus the I o'clock hour line ET3 must make an angle on a Madras dial of only 3° 28' with the meridian EA, 11° 51' on a London dial, 12° 31'at Edinburgh, and 14° 25'at Hammerfest. In the same way may be found the angles made by the other hour lines. The calculations of these angles must extend throughout one quadrant from noon to vi o'clock, but need not be carried further, because all the other hour-lines can at once be deduced from these. _In the first place the dial is symmetrically divided by the meridian, and therefore two times equidistant from noon will have their hour lines equidistant from the meridian ; thus the XI o'clock line and the I o'clock line must make the same angles with it, the xi o'clock the came as the n o'clock, and so on. And next, the 24 great circles, which were drawn to determine these lines, are in reality only 12 ; for clearly the great circle which gives I o'clock after midnight, and that which gives I o'clock after noon, are one and the same, and so also for the other hours. Therefore the hour lines between vi in the evening and VI the next morning are the prolongations of the remaining twelve. Let us now remove the imaginary sphere with all its circles, and retain only the style EP and the plane HMA with the lines traced on it, and we shall have the horizontal dial. On the longest clay in London the sun rises a little after 4 o'clock, and sets a little before 8 o'clock; there is there-fore no necessity for extending a London dial beyond those hours. At Edinburgh the limits will be a little longer, while at Hammerfest, which is within the Arctic circle, the whole circuit will be required. Instead of a wire style it is often more convenient to use a metal plate from one quarter to half an inch in thickness. This plate, which is sometimes in the form of a right-angled triangle, must have an acute angle equal to the latitude of the place, and, when properly fixed in a vertical position on the dial, its two faces must coincide with the meridian plane, and the sloping edges formed by the thickness of the plate must point to the pole and form two parallel styles. Since there are two styles, there must be two dials, or rather two half dials, because a little consideration will show that, owing to the thickness of the plate, these styles will only one at a time cast a shadow. Thus the eastern edge will give the shadow for all hours before 0 o'clock in the morning. From C o'clock until noon the western edge will be used. At noon, it will change again to the eastern edge until 6 o'clock in the evening, and finally the western edge for the remaining hours of daylight. The centres of the two dials will be at the points where the styles meet the dial face; but, in drawing the hour-lines, we must be careful to draw only those lines for which the corresponding style is able to give a shadow as explained above. The dial will thus have the appear-ance of a single dial plate, and there will be no confusion (see %. 3). The line of demarcation between the shadow and the light will be better defined than when a wire style is used ; but the indications by this double dial will always be one minute too fast in the morning and one minute too slow in the afternoon. This is owing to the magnitude of the sun, whose angular breadth is half a degree. The well-defined shadows are given, not by the centre of the sun, as we should require them, but by the forward limb in the morning and by the backward one in the afternoon; and the sun takes just about a minute to advance through a space equal to its half-breadth. Dials of this description are frequently met with in the country. Placed on an ornamental pedestal some 4 feet high, they form a pleasing and useful addition to a lawn or to a garden terrace. The dial plate is of metal as well as the vertical piece upon it, and they may be purchased ready for placing on the pedestal,the dial with all the hour-lines traced on it, and the style-plate firmly fastened in its proper position, if not even cast in the same piece with the dial-plate. When placing it on the pedestal care must be taken that the dial be perfectly horizontal and accurately oriented. The levelling will be done with a spirit-level, and the orien-tation will be best effected either in the forenoon or in the afternoon, by turning the dial-plate till the time given by the shadow (making the one minute correction mentioned above) agrees with a good watch whose error on solar time is known. It is, however, important to bear in mind that a dial, so built up beforehand, will have the angle at the base equal to the latitude of some selected place, such as London, and the hour-lines will be drawn in directions calculated for the same latitude. Such a dial can therefore not be used near Edinburgh or Glasgow, although it would, without appreciable error, be adapted to any place whose latitude did not differ more than 20 or 30 miles from that of London, and it would be safe to employ it in Essex, Kent, or Wiltshire. == TABLE == If a series of such dials were constructed, differing by 30 miles in latitude, then an intending purchaser could select one adapted to a place whose latitude was within 15 miles of his own, and the error of time would never exceed a small fraction of a minute. The following table will enable us to check the accuracy of the hour-lines and of the angle of the style,all angles on the dial being readily measured with an ordinary protractor. It extends from 50° lat. to 59|° lat., and therefore includes the whole of Great Britain and Ireland : == TABLE == Vertical South Dial.Let us take again our imaginary trans-parent sphere QZPA (fig. 4), whose axis PEp is parallel to the earth's axis. Let Z be the zenith, and consequently, the great circle QZP the meridian. Through E, the centre of the sphere, draw a vertical plane facing south. This will cut the sphere in the great circle ZMA which, being vertical, will pass through the zenith, and, facing south, will be at right angles to the meridian. Let QMa be the equatorial circle, obtained by drawing a plane through E at right angles to the axis PEp. The lower portion Ep of the axis will be the style, the vertical line EA in the meridian plane will be the xn o'clock line, and the hori-zontal line EM1 will be the VI o'clock line. Now, as in the pre-vious problem, divide the equatorial circle into 24 equal arcs of 15° each, beginning at a, viz., ab, be, &c.,each quadrant all, MQ, &c, containing six,then through each point of division and through the axis Pp draw a plane cutting the sphere in 24 equidistant great circles. As the sun revolves round the axis the shadow of the axis will successively fall on these circles at intervals of one hour, and if these circles cross the vertical circle ZilA in the points A, B, C, &c, the shadow of the lower portion Ep of the axis will fall on the lines EA, EB, EC, &c, which will therefore be the required hour lines on the vertical dial, Ep being the style. There is no necessity for going beyond the vi o'clock hour-line on each side of noon ; for, in the winter months the sun sets earlier than 6 o'clock, and in the summer months it passes behind the plane of the dial before that time, and is no longer available. It remains to show how the angles AEB, AEC, <fec, may be calculated. The spherical triangles pAB, pAC, &c, will give us a simple rule. These triangles are all right-angled at A, the side pA, equal to ZP, is the co-latitude of the place, that is, the differ-ence between the latitude and 90°; and the successive angles ApB, ApC, &c. are 15°, 30°, &c, respectively. Then tan. AB=tan. 15° sin. co-latitude; or more simply, tan. AB = tan. 15° cos. latitude, tan. AC=tan. 38° cos. latitude, &e., &c. and the arcs AB, AC so found are the measure of the angles AEB, AEC, &e., required. London (51" 30' N. lat.) Log. tan. 15° 9-42805 Log. cos. 51° 30' 9-79415 "We shall, as examples, calculate the I o'clock hour angle AEB for each of the four places we had already taken in the horizontal dial. Madras (18' 4' N. lat.) Log. tan. 15°. 9-42805 Log. cos. 13° 4' 9-98861 Hammorfcst (73" 40' N. lat.) Log. tan. 15° 9-42805 Log. cos. 73° 40' 9-44905 Log. tan. 14° 38'.....9-41666 Log. tan. 9° 28' 9'22220 Edinburgh (55° 57' N. lat.) Log. tan. 15° 9-42S05 Log. cos. 55° 57' 974812 Log. tan. 8° 32'. 9-17617 Log. tan. 4° 19'. In this case the angles diminish as the latitudes increase, the opposite result to that of the horizontal dial. 1 EM is obviously horizontal, since M is the intersection of two great circles ZM, QM, each at right angles to the vertical plane QZP. Inclining, Reclining, &c, Dials.-We shall not enter into the calculation of these cases. Our imaginary sphere being, as before supposed, constructed with its centre at the centre of the dial, and all the hour-circles traced upon it, the intersection of these hour-circles with the plane of the dial will determine the hour-lines just as in the previous cases ; but the triangles will no longer be right-angled, and the simplicity of the calculation will be lost, the chances of error being greatly increased by the difficulty of drawing the dial-plane in its true position on the sphere, since that true position will have to be found from obser-vations which can be only roughly performed. In all these cases, and in cases where the dial surface is not a plane, and the hour-lines, consequently, are not straight lines, the only safe practical way is to mark rapidly on the dial a few points (one is sufficient when the dial face is plane) of the shadow at the moment when a good watch shows that the hour has arrived, and afterwards connect these poiuts with the centre by a continuous line. Of course the style must have been accurately fixed in its true position before we begin. Equatorial Dial.The name equatorial dial is given to one whose plane is at right angles to the style, and therefore parallel to the equator. It is the simplest of all dials. A circle (fig. 5) divided into 24 equal arcs is placed at right angles to the style, and hour divisions are marked upon it. Then if eare be taken that the style point accurately to the pole, and that the noon division coincide with the meridian plane, the shadow of the style will fall on the other divisions, each at its proper time. The divisions must be 5- marked on both sides of the dial, because the sun will shine on opposite sides in the summer and in the winter months, changing at each equinox. To find the Meridian Plane.We have, so far, assumed the meridian plane to be accurately known ; we shall pro-ceed to describe some of the methods by which it may be found. The mariner's compass may be employed as a first rough approximation. It is well known that the needle of the compass, when free to move horizontally, oscillates upon its pivot and settles in a direction termed the magnetic meridian. This does not coincide with the true north and south line, but the difference between them is generally known with tolerable accuracy, and is called the variation of the compass. The variation differs widely at different parts of the surface of the earth, being now about 20° W. in London, 7° W. in New York, and 17° E. in San Francisco. Nor is the variation at any place stationary, though the change is slow. We said that now the variation in London is about 20° W. ; in 1837 it was about 24° W.; and there is even a small daily oscillation which takes place about the mean position, but too small to need notice here. "With all these elements of uncertainty, it is obvious that the compass can only give a rough approximation to the position of the meridian, but it will serve to fix the style so that only a small further alteration will be necessary when a more perfect determination has been made. A very simple practical method is the following : Place a table (fig. 6), or other plane surface, in such a position that it may receive the sun's rays both in the morning and in the afternoon. Then carefully level the surface by means of a spirit-level. This must be done very accurately, and the table in that position made perfectly secure, so that there be no danger of its shifting during the day. Next, suspend a plummet SH from a point S, which must be rigidly fixed. The extremity H, where the plum-met just meets the surface, should be somewhere near the middle of one end of the table. With H for centre, describe any number of concentric arcs of circles, AB, CD, EF, &c. A bead P, kept in its place by friction, is threaded on the plummet line at some convenient height above H. Every thing being thus prepared, let us follow the shadow of the bead P as it moves along the surface of the table during the day. It will be found to describe a curve ACE .... FDB, approaching the point H as the sun advances towards noon, and receding from it afterwards. (The curve is aconic sectionan hyperbola in these regions.) At the moment when it crosses the arc AB, mark the point A; AP is then the direction of the sun, and, as AH is horizontal, the angle PAH is the altitude of the sun. In the afternoon mark the point B where it crosses the same arc ; then the angle PBH is the altitude. But the right-angled triangles PHA, PHB are obviously equal; and the sun has therefore the same altitudes at those two instants, the one before, the other after noon. It follows that, if the sun has not changed its declination during the interval, the two positions will be symmetrically placed one on each side of the meridian. Therefore, drawing the chord AB, i and bisecting it in M, HM will be the meridian line. Each of the other concentric arcs, CD, EF, <fcc, will furnish its meridian line. Of course these should all coincide, but if not, the mean of the positions thus found must be taken. The proviso mentioned above, that the sun has not changed its declination, is scarcely ever realized; but the change is slight, and may be neglected, except per-haps about the time of the equinoxes, at the end of March and at the end of September. Throughout the remainder of the year the change of declination is so slow that we may safely neglect it. The most favourable times are at the end of June and at the end of December, when the sun's declination is almost stationary. If the line H1I be produced both ways to the edges of the table, then the two points on the ground vertically below those on the edges may be found by a plummet, and, if permanent marks be made there, the meridian plane, which is the vertical plane passing through these two points, will have its position perfectly secured. To place the Style of a Dial in its True Position. Before giving any other method of finding the meridian plane, we shall complete the construction of the dial, by showing how the style may now be accurately placed in its true position. The angle which the style makes with a hanging plumb-line, being the co-latitude of the place, is known, and the north and south direction is also roughly given by the mariner's compass. The style may therefore be already adjusted approximatelycorrectly, indeed, as to its inclinationbut probably requiring a little horizontal motion east or west. Suspend a fine plumb-line from some point of the style, then the style will be properly adjusted if, at the very instant of noon, its shadow falls exactly on the plumb-line,or, which is the same thing, if both shadows coincide on the dial. This instant of noon will be given very simply by the meridian plane, whose position we have secured by the two permanent marks on the ground. Stretch a cord from the one mark to the other. This will not generally be horizontal, but the cord will be wholly in the meridian plane, and that is the only necessary condition. Next, suspend a plummet over the mark which is nearer to the sun, and, when the shadow of the plumb-line falls on the stretched cord, it is noon. A signal from the observer there to the observer at the dial enables the latter to adjust the style as directed above. Other Methods of finding the Meridian Plane.-We have dwelt at some length on these practical operations because they are simple and tolerably accurate, and because they want neither watch, nor sextant, nor telescopenothing more, in fact, than the careful observation of shadow lines. The polar star may also be employed for finding the meridian plane without other apparatus than plumb-lines. This star is now only about 1° 21' from the pole ; if there-fore a plumb-line be suspended at a few feet from the observer, and if he shift his position till the star is exactly hidden by the line, then the plane through his eye and the plumb-line will never be far from the meridian plane. Twice in the course of the 24 bours the planes would be strictly coincident. This would be when the star crosses the meridian above the pole, and again when it crosses it below. If we wished to employ the method of determin-ing the meridian, the times of the stars crossing would have to be calculated from the data in the Nautical Almanac, and a watch would be necessary to know when the instant arrived. The watch need not, however, be very accurate, because the motion of the star is so slow that an error of ten minutes in the time would not give an error of one-eighth of a degree in the azimuth. The following accidental circumstance enables us to dis-pense with both calculation and watch. The right ascen-sion of the star -q Ursce Majoris, that star in the tail of the Great Bear which is farthest from the " pointers," happens to differ by a little more than 12 hours from the right ascension of the polar star. The great circle which joins the two stars passes therefore close to the pole. When the polar star, at a distance of about 1|° from the pole, is crossing the meridian above the pole, the star r/ Ursce Majoris, whose polar distance is about 40°, has not yet reached the meridian below the pole. When -i) Ursce Majoris reaches the meridian, which will be within half an hour later, the polar star will have left the meridian; but its slow motion will have carried it only a very little distance away. Now at some instant between these two timesmuch nearer the latter than the former the great circle joining the two stars will be exactly vertical; and at this instant, which the observer determines by seeing that the plumb-line hides the two stars simultaneously, neither of the stars is strictly in the meridian; but the deviation from it is so small that it may be neglected, and the plane through the eye and the plumb-line taken for meridian plane. In all these cases it will be convenient, instead of fixing the plane by means of the eye and one fixed plummet, to have a second plummet at a short distance in front of the eye ; this second plummet, being suspended so as to allow of lateral shifting, must be moved so as always to be between the eye and the fixed plummet. The meridian plane will be secured by placing two permanent marks on the ground, one under each plummet. This method, by means of the two stars, is only available for the upper transit of Polaris ; for, at the lower transit, the other star r¡ Ursce Majoris would pass close to or beyond the zenith, and the observation could not be made. Also the stars will not be visible when the upper transit takes place in the day-time, so that one-half of the year is lost to this method. Neither could it be employed in lower latitudes than 40° N., for there the star would be below the horizon at its lower transit;we may even say not lower than 45° N., for the star must be at least 5° above the horizon before it becomes distinctly visible. There are other pairs of stars which could be similarly employed, but none so convenient as these two, on account of Polaris with its very slow motion being one of the pair. To place the Style in its True Position without previous determination of the Meridian Plane,The various methods given above for finding the meridian plane have for ultimate object the determination of the plane, not on its own account, but as an element for fixing the instant of noon, whereby the style may be properly placed. We shall dispense, therefore, with all this preliminary work if we determine noon by astronomical observation. For this we shall want a good watch, or pocket chronometer, and a sextant or other instrument for taking altitudes. The local time at any moment may be determined in a variety of ways by observation of the celestial bodies. The simplest and most practically useful methods will be found described and investigated in any good educational work on astronomy. For our present purpose a single altitude of the sun taken in the forenoon will be most suitable. At some time in the morning, when the sun is high enough to be free from the mists and uncertain refractions of the horizonbut to insure accuracy, while the rate of increase of the altitude is still tolerably rapid, and, therefore, not later than 10 o'clocktake an altitude of the sun, an assistant, at the same moment, marking the time shown by the watch. The altitude so observed being properly corrected for refraction, parallax, &c, will, together with the latitude of the place, and the sun's declination, taken from the Nautical Almanac, enable us to calculate the time. This will be the solar or apparent time, that is, the very time we require ; and we must carefully abstain from applying the equation of time. Comparing the time so found with the time shown by the watch, we see at once by how much the watch is fast or slow of solar time ; we know, therefore, exactly what time the watch must mark when solar noon arrives, and waiting for that instant we can fix the style in its proper position as explained before. We can dispense with the sextant and with all calcula-tion and observation if, by means of the pocket chronometer, we bring the time from some observatory where the work is done ; and, allowing for the change of longitude, and also for the equation of time, if the time we have brought is clock time, we shall have the exact instant of solar noon as in the previous case. In remote country districts a dial will always be of use to check and even to correct the village clock; and the description and directions here given will, we think, enable any ingenious artisan to construct one. In former times the fancy of dialists seems to have run riot in devising elaborate surfaces on which the dial was to be traced. Sometimes the shadow was received on a cone, sometimes on a cylinder, or on a sphere, or on a combination of these. A universal dial was constructed of a figure in the shape of a cross; another universal dial showed the hours by a globe and by several gnomons. These universal dials required adjusting before use, and for this a mariner's compass and a spirit-level were necessary. But it would be tedious and useless to enumerate the various forms designed, and, as a rule, the more complex the less accurate. Another class of useless dials consisted of those with variable centres. They were drawn on fixed horizontal planes, and each day the style had to be shifted to a new position. Instead of honr-li?ies they had hour-points ; and the style, instead of being parallel to the axis of the earth, might make any chosen angle with the horizon. There was no practical advantage in their use, but rather the reverse; and they can only be considered as furnishing material for new mathematical problems. Portable Dials.The dials so far described have been fixed dials, for even the fanciful ones to which reference was just now made were to be fixed before using. There were, however, other dials, made generally of a small size, so as to be carried in the pocket; and these, so long as the sun shone, roughly answered the purpose of a watch. The description of the portable dial has generally been mixed up with that of the fixed dial, as if it had been merely a special case, and the same principle had been the basis of both; whereas there are essential points of difference between them, besides those which are at once apparent. In the fixed dial the result depends on the uniform angular motion of the sun round the fixed style ; and a small error in the assumed position of the sun, whether due to the imperfection of the instrument, or to some small neglected correction, has only a trifling effect on the time. This is owing to the angular displacement of the sun being so rapida quarter of a degree every minute-that for the ordinary affairs of life greater accuracy is not required, as a displacement of a quarter of a degree, or at any rate of one degree, can be readily seen by nearly every person. But with a portable dial this is no longer the case. The uniform angular motion is not now available, because we have no determined fixed plane to which we may refer it. In the new position, to which the observer has gone, the zenith is the only point of the heavens he can at once practically find ; and the basis for the determination of the time is the constantly but very irregularly varying zenith distance of the sun. At sea the observation of the altitude of a celestial body is the only method available for finding local time; but the perfection which has been attained in the construction of the sextant (chiefly by the introduction of telescopes) enables the sailor to reckon on an accuracy of seconds instead of minutes. Certain precautions have, however, to be taken. The observations must not be made within a couple of hours of noon, on account of the slow rate of change at that time, nor too near the horizon, on account of the uncertain refractions there; and the same restrictions must be observed in using a portable dial. To compare roughly the value (as to accuracy) of the fixed and the portable dials, let us take a mean position in Great Britain, say 54° lat., and a mean declination when the sun is in the equator. It will rise at 6 o'clock, and at noon have an altitude of 36°,that is, the portable dial will indicate an average change of one-tenth of a degree in each minute, or two and half times slower than the fixed dial. The vertical motion of the sun increases, however, nearer the horizon, but even there it will be only one-eighth of a degree each minute, or half the rate of the fixed dial, which goes on at nearly the same speed throughout the day. Portable dials are also much more restricted in the range of latitude for which they are available, and they should not be used more than 4 or 5 miles north, or south of the place for which they were constructed. We shall briefly describe two portable dials which were in actual use. Dial on a Cylinder.A hollow cylinder of metal (fig. 7), 4 or 5 inches high, and about an inch in diameter, has a lid which admits of toler- ably easy rotation. A IT "1 hole in the lid receives the style, shaped some- what like a bayonet; and the straight part of the style, which, on account of the two bends, is lower than the lid, projects horizontally out from the cylinder to a distance of 1 or 1|- inches. When not in use the style would be taken out and placed inside the cylinder. A horizontal circle is traced on the cylin-der opposite the projecting style, and this circle is divided into 36 approximately equidistant intervals. These intervals represent spaces of time, and to each division is assigned a date, so that each month has three dates marked as follows :January 10, 20, 31; February 10, 20, 28 ; March 10, 20, 31; April 10, 20, 30, and so on,always the 10th, the 20th, and the last day of each month. Through each point of division a vertical line parallel to the axis of the cylinder is drawn horn top to bottom. Now it will be readily understood that if, upon one of these days, the lid be turned so as to bring the style exactly opposite the date, and if the dial be then placed on a horizontal table so as to receive sun-light, and turned round bodily until the shadow of the style falls exactly on the vertical line below it, the shadow will terminate at some definite point of this line, the position of which point will depend on the length of the stylethat is, the distance of its end from the surface of the cylinderand on the altitude of the sun at that instant. Suppose that the observations are continued all day, the cylinder being very gradually turned so that the style may always face the sun, and suppose that marks are made on the vertical line to show the extremity of the shadow at each exact hour from sunrise to sunsetthese times being taken from a good fixed sun dial,then it is obvious that the next year, on the same date, the sun's declination being about the same, and the observer in about the same latitude, the marks made the previous year will serve to tell the time all that day. Constrvction.Draw a straight line ACB parallel to the top of the card (fig. 8) and another DCE at right angles to it; with C as centre, and any convenientTadius CA, describe the semi-circle AEB belovi the horizontal. Divide the -whole arc AEB into 12 equal parts at the points r, s, t, &c, and through these points draw perpendi-culars to the diameter ACB, these lines mil he the hour lines, viz., the line through r will be the xi ..i line ; the line through s the line, and so on ; the hour line of noon viiH be the point A What we have said above was merely to make the principle of the instrument clear, for it is evident that this mode of marking, which would require a whole year's sunshine and hourly observation, cannot be the method employed. The positions of the marks are, in fact, obtained by calculation. Corresponding to a given date, the declination of the sun is taken from the almanac, and this, together with the latitude of the place and the length of the style, will constitute the necessary data for computing the length of the shadow, that is, the distance of the mark below the style for each successive hour. We have assumed above that the declination of the sun is the same at the same date in different years. This is not quite correct, but, if the dates be taken for the second year after leap year, the results will be sufficiently approxi-mate. The actual calculations will oSer no difficulty. When all the hour marks have been placed opposite to their respective dates, then a continuous curve, fining the corresponding hour-points, will serve to find the time for a day intermediate to those set down, the lid being turned till the style occupy a proper position between the two divisions. The horizontality of the surface on which the instrument rests is a very necessary condition, especially in summer, when, the shadow of the style being long, the extreme end will shiit rapidly for a small deviation from the vertical, and render the reading uncertain. The dial can also be used by holding it up by a small ring in the top of the lid, and prcbably the verticality is better ensured in that way. Portable Dial on a Card.This neat and very ingenious dial is attributed by Ozanam to a Jesuit Father, De Saint liigaud, and probably dates from the early part of the 17th century. Ozanam says that it was sometimes called the capuchin, from some fancied resemblance to a cowl thrown back. itseli ; by subdivision of the small ares Ar, rs, st, kc, we may draw the hour lines corresponding to halves and quarters, but this only where it can be done without confusion. Draw ASD making with AC an angle equal to the latitude of the place, and let it meet EC in D, through which point draw FD6 at right angles to AD. With centre A, and any convenient radius AS, describe an arc of circle RST, and graduate this arc by marking degree divisions on it, extending from 0° at S to 23J° on each side at R and T. Next determine the points on the straight line FDG where radii drawn from A to the degree divisions on the arc would cross it, and care-fully mark these crossings. The divisions of RST are to correspond to the sun's declination, south declinations on RS and north declinations on ST. In the other hemisphere of the earth this would be reversed ; the north declinations would be on the upper half. Now, taking a second year after leap yer.r (because the declina-tions of that year are about the mean of each set of four years), find the days of the month when the sun has these different declina-tions, and place these dates, or so many of them as can be shown without confusion, opposite the corresponding marks on FDG. Draw the sun-line at the top of the card parallel to the line ACB ; and, near the extremity, to the right, draw any small figure intended to form, as it were, a door of which a b shall be the hinge. Care must be taken that this hinge is exactly at right angles to the sun-line. Make a fine open slit c d right through the card and extending from the hinge to a short distance on the door,the centre line of this slit coinciding accurately with the sun-line. Now, cut the door completely through the card ; except, of course, along the hinge, which, when the card is thick, should be partly cut through at the back, to facilitate the opening. Cut the card right through along the line FDG, and pass a thread carrying a little plummet W and a very small bead P ; the bead having sufficient friction with the thread to retain any position when acted on only by its own weight, but sliding easily along the thread when moved by the hand. At the back of the card the thread terminates in a knot to hinder it from being drawn through ; or better, because giving more friction and abetter hold, it passes through the centre of a small disc of carda f rac tion of an inch In diameterand, by a knot, is made fast at the back of the disc. To complete the construction,with the centres F and G, and radii FA and GA, draw the two arcs AY and AZ which will limit the hour lines; for in an observation the bead will always be found between them. The forenoon and afternoon hours may then be marked as indicated in the figure. The dial does not of itself dis-criminate between forenoon and afternoon ; but extraneous circum-stances, as, for instance, whether the sun is rising or falling, will settle that point, except when close to noon, where it will always be uncertain. To rectify the dial (using the old expression, which means to pre-pare the dial for an observation),open the small door, by turning it about its hinge, till it stands well out in front. Next, set the thread in the line FG opposite the day of the month, and stretching it over the point A, slide the bead P along till it exactly coincide with A. To find the hour of the day,hold the dial in a vertical position in such a way that its plane may pass through the sun. The verti-cality is ensured by seeing that the bead rests against the card without pressing. Now gi adually tilt the dial (without altering its vertical plane), until the central line of sunshine, passing through the open slit of the door, just falls along the sun-line. The hour line against which the bead P then rests indicates the time. The sun-line drawn above has always, so far as we know, oeen used as a shadow-line. The upper edge of the rectangular door was the prolongation of the line, and, the door being opened, the dial was gradually tilted until the shadow cast by the upper edge exactly coincided with it. But this shadow tilts the card one-quarter of a degree more than the sun-line, because it is given by that portion of the sun which just appears above the edge, that is, by the upper limb of the sun, which is one-quarter of a degree higher than the centre. Now, even at some distance from noon, the sun will sometimes take a considerable time to rise one-quarter of a degree, and by so much time will the indication of the dial be in error. The central line of light which comes through the open slit will be free from this error, because it is given by light from the centre of the sun. The card-dial deserves to be looked upon as something more than a mere toy. Its ingenuity and scientific accuracy give it an educa-tional value which is not to be measured by the roughness of the results obtained, and the following demonstration of its correct-ness will, it is hoped, usefully close what we have to say on this subject. Demonstration.Let H (fig. 9) be the point of suspension of the plummet at the time of observation, so that the angle DAH is the north declination of the sun, P, the bead, resting against the hour-line YX. Join OX, then the angle ACX is the hour angle from noon given by the bead, and we have to prove that this hour-angle is the correct one corresponding to a north latitude DAC, a north declination AH and an altitude equal to the angle which the sun-line, or its parallel AC, makes with the horizontal. The angle PHQ will be equal to the altitude, if HQ be drawn parallel to DC, for the pair of lines HQ, HP will be respectively at right angles to the sun-line and the horizontal. Draw PQ and JIM parallel to AC, and let them meet DCE in M and N respectively. Let HP and its equal HA be represented by a. Then the follow- ing values will be readily deduced from the figure : AD a cos. decl., DH = a sin. decl., PQ a sin. alt. CX = AC = AD cos. lat. a cos. decl. cos. lot. PN = CV = CX cos. ACX = a cos. decl. cos. lat. cos. ACX. NQ = MH = DH sin. M DH =a sin. iecl. sin. lat. (o_othe angle MDH - DAC = latitude). And, since PQ = NQ + PN, we have, by simple substitution, a sin. alt. a sin. decl. sin. lat. +a cos. decl. cos. lat. cos ACX ; or, dividing by a throughout. sin. alt. =sin. decl. sin. lat. +cos. decl. cos. lat. cos. ACX . . . (At wnich equation determines the hour angle ACX shewn by the bead. To determine the hour-angle of the sun at the same moment, let fig. 10 lepresent the celestial sphere, HR the horizon, P the poley and Z the zenith, and S the sun. From the spherical triangle PZS, we have cos. ZS=eos. PS cos. ZP + sin. PS sin. ZP cos. ZPS but ZS = zenith distance = 90°-altitude ZP-90°-PR -90° -latitude PS = polar distance = 90° - declination, therefore, by substitution sin. alt. =sin. decl. sin. lat. + cos. dccl. cos. lat. cos. ZPS . . . (B) and ZPS is the hour-angle of the sun. A comparison of the two formula; (A) and (B) shows that the hour-augle given by the bead will be the same as that given by the sun, and proves the theoretical accuracy of the card-dial. Just at sun-rise or at sun-set, the amount of refraction slightly exceeds half a degree. If, then, a little cross m (see fig. 8) be made just below the sun-line, at a distance from it which would subtend half a degree at c, the time of sunset would be found corrected for refrac-tion, if the central line of light were made to fall on cm. The following list includes the principal writers on dialling whose works have come down to us, and to these we must refer for descriptions of the various constructions, some simple and direct, others fancitul and intricate, which have been at different times employed : Ptolemy, Ana-lemma, restored by Commandine ; Vitruvius, Architecture ; Sebastian Munster, Horologiographia ; Orontius Fineus, De Ilorologiis Solaribus; Mutio Oddi da Urbino, Horologi Solari; Dryander, De Horologiorum Compositions ; Conrad Gesner, Pandectce ; Andrew Schoner, Gnomonica;; F. Commandine, Horolo-giorum Descriplio ; Joan. Bapt. Benedictas, De Gnomonum XJsu ; Georgius Schömberg, Exegesis Fundamentorum Gnomonicorum ; Joan. Solomon de Caus, Horologes Solaires ; Joan. Bapt. Trolta, Praxis Horologiorum ; Uesargues, Manière Universelle pour poser l'Essieu, &c. ; Ath. Kircher, Ars magna Lucis et Umbra ; Hallum, Explicatio Horologii in Horto Regio Fondini ; Joan. Mark, Tracta-tus Horologiorum ; Clavius, Gìiomonices de Ilorologiis. Also among more modem writers, Deschales, Ozanam, Schottus, Wollius, Picard, Lahire, Walper ; in German, Paterson, Michael, Müller ; and among English writers, Foster, Wells, Collins, Lead- better, Jones, Leybourn, Emerson, and Ferguson. See also Meikle's article in former editions of the present work. (H. G.) In one of the Courts of Queen's College, Cambridge, there is an elaborate sun-dial dating from the end of the 17th or beginning of the 18th century, and around it a series of numbers which make it avail-able as a moon-dial when the moon's age Is known.

Something abnormal is cruising toward us. Something little and cold and uncommonly quick. Nobody knows where it originated from, or where it is going. However, it’s not from around here. This is an interstellar comet – an old chunk of ice and gas and residue, framed on the solidified edges of a far off star, which some fortunate characteristic of gravity has hurled into our way. To space experts, the comet is a consideration bundle from the universe – a bit of a spot they will always be unable to visit, a key to every one of the universes they can’t legitimately watch. It is just the second interstellar intruder researchers have found in our nearby planetary group. Also, it’s the first they’ve had the option to get a decent take a gander at. By following the comet’s development, estimating its sythesis and checking its conduct, analysts are looking for pieces of information about the spot it originated from and the space it crossed to arrive. They have just discovered a carbon-based particle and potentially water – two natural synthetic compounds in such an outsider item. As the Sun sinks behind the Tennessee mountains, and stars wink into see, cosmologist Doug Durig ascends onto the housetop of his observatory, controls up his three telescopes and points them skyward. Consistently, the comet becomes greater and more brilliant in the sky, ousting surges of gas and residue that may present pieces of information to its history. On Dec. 8, it will make its closest way to deal with Earth, offering scientists a very close look before it zooms once more into the solidifying, featureless void.

In newly released footage from the University of Western Ontario, a bright, slow-moving fireball was captured in the skies near Toronto, Canada on December 12, 2011 by remote cameras watching for meteors. Although this meteor looks huge as it burns up in Earth’s atmosphere, astronomers estimate the rock to have been no bigger than a basketball. Footage reveals it entered the atmosphere at a shallow angle of 25 degrees, moving about 14 km per second. It first became visible over Lake Erie then moved toward the north-northeast. See below for the video. But in a meteorite-hunter alert, Peter Brown, the Director of Western’s Centre for Planetary & Space Exploration said that data garnered from the remote cameras suggest that surviving fragments of the rock are likely, with a mass that may total as much as a few kilograms, likely in the form of many fragments in one gram to hundreds of a gram size range. “Finding a meteorite from a fireball captured by video is equivalent to a planetary sample return mission,” said Brown. “We know where the object comes from in our solar system and can study it in the lab. Only about a dozen previous meteorite falls have had their orbits measured by cameras so each new event adds significantly to our understanding of the small bodies in the solar system. In essence, each new recovered meteorite is adding to our understanding of the formation and evolution of our own solar system.” Brown and his team are interested in hearing from anyone who may have witnessed or recorded this event, or who may have found fragments of the freshly fallen meteorite. See UWO’s website for contact information. Another camera view of the meteor: Western Meteor Group’s Southern Ontario Meteor Network sensor suite has seven all-sky video systems designed to automatically detect bright fireballs. At 6:04 p.m. on December 12, six of the seven cameras of Western’s Southern Ontario Meteor Network recorded this meteor. In a press release, UWO said the fireball’s burned out at an altitude of 31 km just south of the town of Selwyn, Ontario. It is likely to have dropped small meteorites in a region to the east of Selwyn near the eastern end of Upper Stony Lake. See the map of the projected path below. Although this bright fireball occurred near the peak of the annual Geminid meteor shower, the astronomers say it is unrelated to that shower.

Authors: GRAVITY Collaboration: S. Lacour, M. Nowak, J. Wang, et. al. First Author’s Institution: LESIA, Observatoire de Paris, Universite PSL, CNRS, Sorbonne Universite, Univ. Paris Diderot, Max Planck Institute for Extraterrestrial Physics Status: Published in Astronomy & Astrophysics [closed access] and arXiv [open access] TRAPPIST-1 might be the best known system with multiple planets, but HR 8799 has quite a few cool things going for it, too. It’s one of the first systems discovered with direct imaging (actually taking pictures of the planets themselves), and since then people have been observing its four planets moving around in their orbits. The kinds of planets we see around HR 8799 are also very different than those around TRAPPIST-1. The transit method, used to discover the 7 terrestrial TRAPPIST-1 planets, is better suited to find planets very close to their host stars. Direct imaging, on the other hand, is best for the biggest, furthest out planets – young super-Jupiters and brown dwarfs, orbiting 10s to 100s of AU from their stars. Direct imaging is also able to provide useful information about planetary orbits – it’s really clear to see where each of the HR 8799 planets is (as in Figure 1), whereas with the transit or radial velocity methods it takes a bit more untangling to sort through the overlapping signals of multiple planets. The goal is to determine the orbits, masses, and compositions of these kinds of giant planets, so that we can understand what they’re like and how they formed. For example, looking at the composition of the atmosphere, we can observe how much carbon there is compared to oxygen (the C/O ratio) to figure out where it formed in the protoplanetary disk. The D/H ratio (deuterium to hydrogen) can tell us about how many icy bodies (like Kuiper Belt Objects) a planet must have accreted in its past. This all sounds great, having a way to trace the formation of big planets – so what’s the catch? Because of the immense challenges of directly imaging a faint exoplanet around a bright star and the limited sizes of our telescopes, we don’t have the spatial resolution needed to really precisely constrain the orbits of these planets or see fine details in their spectra. That’s where today’s paper comes in, describing the first observations of an exoplanet using optical interferometry, a technique that allows for higher spatial resolution by combining multiple telescopes in clever ways. Interferometry comes up a lot in radio astronomy, such as with ALMA or the recent black hole image from the Event Horizon Telescope. It’s possible to use this same technique for optical/visible light, too. The idea is to use multiple telescopes, separated by some distances (known as the baselines), to collect light from an object simultaneously. It’s possible to combine these observations, and then it’s as if you’re observing with a “virtual” telescope the size of the baseline, which is much larger than any one individual telescope mirror. A larger telescope means better spatial resolution, which is exactly what we need to constrain the orbits and spectra of directly imaged planets. The authors used the ESO’s VLTI (Very Large Telescope Interferometer) and its GRAVITY instrument to use this technique on one of the HR 8799 planets – specifically, planet e, the one closest to the star. This is a really tricky process, since it requires precise knowledge of the telescope position and movement and more. But, they did it, and obtained the most precise astrometry (position information) of HR 8799 e yet. Their measurements narrowed down the position to tens of microarcseconds, orders of magnitude more precise than what direct imaging has done (see Figure 2). Combined with some previous analysis of the orbits of the whole HR 8799 system, this observation shows us that the planets around HR 8799 aren’t coplanar – that is, some of them must have orbits that are tilted relative to the plane of the whole system. GRAVITY can also do spectroscopy – see Figure 3 for the spectrum of HR 8799 e! The authors compared this to atmospheric models, which generate spectra for different kinds of atmospheres that the authors can then compare to the observed spectrum. They determined that HR 8799 e is likely an L-type brown dwarf, with a cool temperature of around 1150 K. Observations like this can help tease out what’s going on with the L/T transition, an important evolutionary stage for brown dwarf atmospheres. Many other planetary systems should be observable with GRAVITY, and the team has already set their sights on some of the well-known directly imaged planets, like Beta Pictoris b. Overall, this is an exciting first result for a promising new technique – orbital monitoring and spectroscopy with this precision can really help us understand directly imaged systems. In the future, larger baseline interferometry could maybe even resolve exoplanetary surfaces, showing clouds and other features!

Does a permanently shadowed crater at the Moon’s South Pole harbor frozen water? Enough to supply a lunar outpost? How much ultraviolet and cosmic radiation would astronauts be exposed to if they stayed on the moon for a week or longer? Where are the best—and worst—landing sites on the Moon? These are some of the questions that NASA plans to answer with its two new lunar missions. After waiting out a thunderstorm, NASA’s Lunar Reconnaissance Orbiter and Lunar Crater Observation and Sensing Satellite rocketed off the launch pad at Kennedy Space Center in Cape Canaveral, Florida, at 5:32 p.m. Eastern Daylight Time on June 18, 2009. This photograph captures the pair of spacecraft as they were lifting off. In under than two minutes, the spacecrafts had reached an altitude of 11.3 miles and were preparing to ditch the spent rocket that had gotten them off the ground. At 5:46, the second stage rocket fired for the first time, pushing the spacecraft through the atmosphere at more than 12,000 miles per hour. At 6:09, the rocket fired again for five minutes, catapulting the two spacecraft toward the Moon. The Lunar Reconnaissance Orbiter hung on to the coasting rocket for about 8 minutes before separating. In four days, it will reach the Moon, where it will go into orbit just 31 miles above the surface. The Lunar Crater Observation and Sensing Satellite is holding on to the spent rocket. In October, it will hurl the empty rocket toward a crater at the South Pole and use its sensors to figure out whether the resulting debris contains water ice. Later, the spacecraft itself will crash into the crater. The debris kicked up by the collision will be so tremendous that it will probably be visible from Earth with a good amateur telescope. The point of these lunar missions is to collect the kinds of information we need to return astronauts to the moon. But the point of going to the moon is to learn about the Earth and our solar system (and ultimately, the universe). More than four billion years ago, as our solar system was forming, a planetary object roughly the size of Mars smacked into the Earth. The collision shattered the small planet and probably vaporized the upper layers of Earth’s surface. The debris—part Earth, part destroyed planet—remained in orbit around the Earth. Eventually, the debris aggregated into the Moon. If this theory, widely accepted among astrophysicists, is correct, then the formation of the Earth is inextricably tied to the formation of the Moon. And because the Moon’s surface has not been endlessly remodeled by plate tectonics, volcanoes, or erosion, it should be able to tell us things about how the Earth came to be that our planet itself never will. NASA photographs provided courtesy of the Kennedy Space Flight Center Public Affairs Office. Caption by Rebecca Lindsey. After waiting out a thunderstorm, NASA’s Lunar Reconnaissance Orbiter and Lunar Crater Observation and Sensing Satellite rocketed off the launch pad at Kennedy Space Center in Cape Canaveral, Florida, at 5:32 p.m. Eastern Daylight Time on June 18, 2009. This photograph captures the pair of spacecraft as they were lifting off.

Questions about electron degenerate stellar remnants. A white dwarf, also known as a degenerate dwarf, is a type of stellar remnant. It forms from the pressured core during the death of medium stars not capable of exerting enough gravity to overcome electron resistance. White dwarfs have masses on average of about 0.5 to 0.6 Solar Masses, although there are some exceptions. A white dwarf exerts faint luminosity, that will fade over time as the light it emits are from thermal temperature which will run out over time. A white dwarf mainly contains helium with possible heavy elements such as carbon and oxygen, and a debatable coating of hydrogen. If a white draws enough mass(i.e. 1.4 solar masses), electron resistance is overcome by gravity and the white dwarf collapses into a 1a supernova. Once a white dwarf cools, it becomes a black dwarf. No black dwarfs exist due to the cooling time being longer than the current age of the universe.

Where there once was 158, there is now more… Globular clusters, that is. Thanks to ESO’s VISTA survey telescope at the Paranal Observatory in Chile, the Via Lactea (VVV) survey has cut through the gas and dust of the Milky Way to reveal the first star cluster that is far beyond our center. But keep your eyes on the prize, because as dazzling as the cluster called UKS 1 is on the right is, the one named VVV CL001 on the left isn’t as easy to spot. Need more? Then keep on looking, because VVV CL001 isn’t alone. The next victory for VISTA is VVV CL002, which is shown in the image below. What makes it special? It’s quite possible that VVV CL002 is the closest of its type to the center of our galaxy. While you might think discoveries of this type are commonplace, they are actually out of the ordinary. The last was documented in 2010 and it’s only through systematically studying the central parts of the Milky Way in infrared light that new ones turn up. To add even more excitement to the discovery, there is a possibility that VVV CL001 is gravitationally bound to UKS 1, making it a binary pair! However, without further study, this remains unverified. Thanks to the hard work of the VVV team led by Dante Minniti (Pontificia Universidad Catolica de Chile) and Philip Lucas (Centre for Astrophysics Research, University of Hertfordshire, UK) we’re able to feast our eyes on even more. About 15,000 light years away on the other side of the Milky Way, they’ve turned up VVV CL003 – an open cluster. Due the intristic faintness of these new objects, it’s a wonder we can see them at all… In any light! Original Story Source: ESO Press Release.

Scientists using the MeerKAT radio telescope have discovered a unique and previously-unseen flare of radio emission from a binary star in our galaxy. The MeerKAT radio telescope in the Northern Cape of South Africa has discovered an object which rapidly brightened by more than a factor of three over a period of three weeks. This is the first new transient source discovered with MeerKAT and scientists hope it is the tip of an iceberg of transient events to be discovered with the telescope. Astronomers call an astronomical event "transient" when it appears or disappears, or becomes fainter or brighter over seconds, days, or even years. These events are important as they provide a glimpse of how stars live, evolve, and die. Using an assortment of telescopes around the globe, the researchers determined that the source of the flare is a binary system, where two objects orbit each other approximately every 22 days. While the cause of the flaring and the exact nature of the stars that make up the system is still uncertain, it is thought to be associated with an active corona - the hot outermost part of the brighter star. The source of the observed activity is located in the Southern constellation of Ara and was found to be coincident with a giant star about two times as massive as the Sun. The orbital period was determined using optical observations with the Southern African Large Telescope (SALT). Fortuitously, the star is sufficiently bright to have also been monitored by optical telescopes for the last 18 years and is seen to vary in brightness every three weeks, matching the orbital period. "This source was discovered just a couple of weeks after I joined the team, it was amazing that the first MeerKAT images I worked on had such an interesting source in them. Once we found out that the radio flares coincided with a star, we discovered that the star emits across almost the entire electromagnetic spectrum from X-ray to UV to radio wavelengths." said Laura Driessen, a PhD student at The University of Manchester who led this work. Patrick Woudt, Professor and Head of the Astronomy Department at The University of Cape Town said: "Since the inauguration in July 2018 of the South African MeerKAT radio telescope, the ThunderKAT project on MeerKAT has been monitoring parts of the southern skies to study the variable radio emission from known compact binary stars, such as accreting black holes. "The excellent sensitivity and the wide field of view of the MeerKAT telescope, combined with the repeat ThunderKAT observations of various parts of the southern skies, allows us to search the skies for new celestial phenomena that exhibit variable or short-lived radio emission." Professor Ben Stappers from The University of Manchester said: "The properties of this system don't easily fit into our current knowledge of binary or flaring stars and so may represent an entirely new source class." The MeerKAT telescope is sweeping the sky for sources that vary on timescales from milliseconds to years, and will significantly improve human understanding of the variable radio sky. The discovery of this new transient with MeerKAT demonstrates how powerful this telescope will be in the search for further new transient events. Rob Adam, Director of the South African Radio Astronomy Observatory (SARAO) said: "Once again we see the potential of the MeerKAT telescope in finding interesting and possibly new astrophysical phenomena, as well as the power of the multi-wavelength approach to the analysis of observations." Dr. David Buckley from the South African Astronomical Observatory, who leads the SALT (Southern African Large Telescope) transient follow-up programme, commented: "This is a perfect example of where coordinated observations across different wavelengths were combined to give a holistic view of a newly discovered object. "This study was one of the first to involve coordination between two of South Africa's major astronomy facilities and shows the way for future such work."

The Little Ice Age was a period of cooling that occurred after the Medieval Warm Period. Although it was not a true ice age, the term was introduced into scientific literature by François E. Matthes in 1939, it has been conventionally defined as a period extending from the 16th to the 19th centuries, but some experts prefer an alternative timespan from about 1300 to about 1850. The NASA Earth Observatory notes three cold intervals: one beginning about 1650, another about 1770, the last in 1850, all separated by intervals of slight warming; the Intergovernmental Panel on Climate Change Third Assessment Report considered the timing and areas affected by the Little Ice Age suggested independent regional climate changes rather than a globally synchronous increased glaciation. At most, there was modest cooling of the Northern Hemisphere during the period. Several causes have been proposed: cyclical lows in solar radiation, heightened volcanic activity, changes in the ocean circulation, variations in Earth's orbit and axial tilt, inherent variability in global climate, decreases in the human population. The Intergovernmental Panel on Climate Change Third Assessment Report of 2001 described the areas affected: Evidence from mountain glaciers does suggest increased glaciation in a number of spread regions outside Europe prior to the twentieth century, including Alaska, New Zealand and Patagonia. However, the timing of maximum glacial advances in these regions differs suggesting that they may represent independent regional climate changes, not a globally-synchronous increased glaciation, thus current evidence does not support globally synchronous periods of anomalous cold or warmth over this interval, the conventional terms of "Little Ice Age" and "Medieval Warm Period" appear to have limited utility in describing trends in hemispheric or global mean temperature changes in past centuries.... Hemispherically, the "Little Ice Age" can only be considered as a modest cooling of the Northern Hemisphere during this period of less than 1°C relative to late twentieth century levels; the IPCC Fourth Assessment Report of 2007 discusses more recent research, giving particular attention to the Medieval Warm Period. When viewed together, the available reconstructions indicate greater variability in centennial time scale trends over the last 1 kyr than was apparent in the TAR.... The result is a picture of cool conditions in the seventeenth and early nineteenth centuries and warmth in the eleventh and early fifteenth centuries, but the warmest conditions are apparent in the twentieth century. Given that the confidence levels surrounding all of the reconstructions are wide all reconstructions are encompassed within the uncertainty indicated in the TAR; the major differences between the various proxy reconstructions relate to the magnitude of past cool excursions, principally during the twelfth to fourteenth and nineteenth centuries. There is no consensus regarding the time when the Little Ice Age began, but a series of events before the known climatic minima has been referenced. In the 13th century, pack ice began advancing southwards in the North Atlantic, as did glaciers in Greenland. Anecdotal evidence suggests expanding glaciers worldwide. Based on radiocarbon dating of 150 samples of dead plant material with roots intact, collected from beneath ice caps on Baffin Island and Iceland, Miller et al. state that cold summers and ice growth began abruptly between 1275 and 1300, followed by "a substantial intensification" from 1430 to 1455. In contrast, a climate reconstruction based on glacial length shows no great variation from 1600 to 1850 but strong retreat thereafter. Therefore, any of several dates ranging over 400 years may indicate the beginning of the Little Ice Age: 1250 for when Atlantic pack ice began to grow; the Little Ice Age ended in the latter half of the 19th century or early in the 20th century. The Little Ice Age brought colder winters to parts of North America. Farms and villages in the Swiss Alps were destroyed by encroaching glaciers during the mid-17th century. Canals and rivers in Great Britain and the Netherlands were frozen enough to support ice skating and winter festivals; the first River Thames frost fair was in 1608 and the last in 1814. Freezing of the Golden Horn and the southern section of the Bosphorus took place in 1622. In 1658, a Swedish army marched across the Great Belt to Denmark to attack Copenhagen; the winter of 1794–1795 was harsh: the French invasion army under Pichegru was able to march on the frozen rivers of the Netherlands, the Dutch fleet was locked in the ice in Den Helder harbour. Sea ice surrounding Iceland extended for miles in every direction; the population of Iceland fell by half, but that may have been caused by skeletal fluorosis after the eruption of Laki in 1783. Iceland suffered failures of cereal crops and people moved away from a grain-based diet; the Norse colonies in Greenland starved and vanished by the early 15th century, as crops failed and livestock could Hermann Jansen was a German architect, urban planner and university educator. Hermann Jansen was born in 1869 was the son of the pastry chef Francis Xavier Jansen and his wife Maria Anna Catharina Arnoldi. After visiting the humanistic Kaiser-Karls-Gymnasium in Aachen, Jansen studied architecture at the RWTH Aachen University in Karl Henrici. After graduation in 1893, Jansen worked in an architectural office in Aachen. 1897 drew Jansen to Berlin, in 1899 created his own business with the architect William Mueller. In the same year he made the designs for the later-named Pelzer tower in his home town of Aachen. In 1903 he took over the publication of the architecture magazine "The Builder", first published in 1902 in Munich. In the years prior to 1908, the District of Berlin and its surrounding towns and cities had witnessed immense growth due to private investment. Due to the unplanned nature of growth in the city, several key urban challenges surfaced; these included the provision of housing, capacity for efficient transport, the demand for public open spaces. With pressures mounting, the city saw planning a means of directing growth, in 1908 put forth the ‘Groẞ-Berlin' competition. The competition required planners and architects to put forth design that would link central Berlin with surrounding towns in the regions to form a metropolis, spanning from the historic center to outer suburbs. Jansen was among the planners who submitted a comprehensive plan for a Greater Berlin, when the competition closed in 1910 his was awarded equal first place. Jansen's proposal dubbed "The Jansen-plan" stood as the first comprehensive plan to be commissioned for Greater Berlin. Under the Jansen plan, development of Berlin would be arranged around a small inner ring and a larger outer ring of green space comprising parks, gardens and meadows, which would be connected via green-corridors radiating outward from the compact inner-city; the central focus of green space in Jansen's design was well received and laid the foundation for the creation and safeguarding of open spaces across Berlin. In addition to his focus on public space, Jansen's plan received accolades for the attention drawn to overcrowding in central Berlin, with a proposed fast transport system aimed at integrating the center of the city with peripheral areas. What made this aspect of Jansen's plan for Berlin so popular was the creation of positive dwellings in areas of urban expansion; these dwellings came in the form of single houses within small settlements with the intention of creating new opportunities for Berlin's less-privileged social classes to live outside the city center. Due to the onset of World War I, Jansens's plan was only implemented, however evidence of his work can still be found to some extent in the cityscape. Jansen's competition winning work was showcased at the General Town Planning Exhibition held on 1 May 1910 at the Royal Arts Academy, known today as Berlin University of the Arts; the exhibition was among the first to give comprehensive account of planning and the built environment. Following its unexpectedly popular reception in Berlin many sections, including Jansen's plan, were featured at the Town Planning Conference in London that year. In 1918, Jansen was in the Royal Prussian Academy of Arts in Berlin and recorded in their Senate and received the title of professor. On the occasion of his 50th Birthday, he was awarded an honorary doctorate by the Technical University in Stuttgart as the founder and leader of the modern urban art, he was a member of the Advisory Council of the Prussian cities Ministry of Public Works. He was a member of the Association of German Architects. In 1920, Hermann Jansen was appointed as associate professor of urban art at the Technische Hochschule Charlottenburg resigning in 1923. Jansen in 1930 became professor of urban planning at the University of Arts Berlin, he contributed to plans across Germany including. Jansen planned for foreign cities such as Riga, Łódź, Bratislava and Madrid. In the 1930s he prepared a city plan for Mersin, in 1938 the Mersin Interfaith Cemetery was established in one of the locations that he proposed. Following the failure of existing urban planning measures to address the uncontrolled growth experienced in Turkey's newly established capital Ankara, 1927 saw the Turkish Government put forth an international competition to create a comprehensive development plan for the new city. The government invited three prominent European planners to the competition, Frenchman Léon Jaussely and Germans Joseph Brix and Hermann Jansen. In 1929 the competition concluded with the jury declaring Jansen's proposal to be the winner, following which he was commissioned with preparing detailed development plans for the capital city. Jansen's master plan for Ankara placed particular emphasis on the historical context of the region, stressing the importance of the new settlement sitting adjacent to the existing old city rather than enveloping it within the new design. Jansen called for the compulsory integration of green belts and areas within the city to promote a healthy urban environment extending this vision to the housing stock, which were designed to incorporate both front and rear gardens. A defining feature of Jansen's master plan for Ankara was his division of the city into functionally specialized zones, an unfamiliar concept when compared to traditional Turkish urban form; this included 18 residential sections, each Jérémie Pauzié was a Genevan diamond jeweler and memoirist, known for his work for the Russian Imperial court and the Imperial Crown of Russia, which he created with the court's jeweler Georg Friedrich Ekart. Throughout his working life Pauzié, who held the title Principal Diamond Expert and Court Jeweller, made jewellery and gifts for the Russian nobility and the Imperial family, he recorded his life in the book of ‘Memoirs of a Court Jeweller Pauzié, published by the Russian history journal ‘Russkaya Starina’ in 1870. Pauzié studied for seven years with Benedict Gravero in Saint Petersburg, in the end of the 1730s started his own jewellery workshop. Hs speciality was work with diamond and other jewels, he did not have much experience with noble metals. For work on metals, he hired subcontractors. In this period, Pauzié produced jewellery for local noblemen, was admitted to the Imperial court. In 1761, Empress Elizabeth died, Ekart, the chief court jeweller, was charged in making a funeral crown. His solution proved to be suboptimal, Pauzié was asked to repair the crown. After that, he got access to the court, was considered to be Ekart's chief rival; when the reign of Catherine the Great started, Ekart was charged with making the Imperial Crown, Pauzié decorated it with jewels, against Ekart's will. In 1764, Pauzié left Saint Petersburg and went back to Switzerland, where in 1770 he became the citizen of Geneva. Pauzié was commissioned to work with Ekart, the Russian Imperial court's jeweler, to create the Great Imperial Crown of Russia, created for the coronation of Catherine the Great in 1762; the crown was made in the style of classicism and constructed of two gold and silver half spheres, representing the eastern and western Roman empires, divided by a foliate garland and fastened with a low hoop. The crown contains 75 pearls and 4,936 Indian diamonds forming laurel and oak leaves, the symbols of power and strength, is surmounted by a 398.62 carat ruby spinel that belonged to the Empress Elizabeth, a diamond cross. After Catherine the Great's coronation the crown continued to be used as the coronation crown of all Romanov emperors, till the monarchy's abolition and the death of last Romanov, Nikolas II in 1918. It is considered to be one of the main treasures of the Romanov dynasty, is now on display in the Moscow Kremlin Armoury Museum in Russia, his work formed part of the art jewellery exhibitions, including The Art of the Goldsmith & the Jeweler at A La Vieille Russie in New York and Carl Fabergé and Masters of Stone Carving: Gem Masterpieces of Russia at the Dormition Belfry of the Moscow Kremlin Museums in Moscow. In 2013 the Jérémie Pauzié name was acquired by French luxury group Vendôme Private Trading. «Culture» Discovery. Escape of the diamond master Pauzié. January, 2015 Notes of the Court Jeweler Jeremie Posier 1729-64, ed. A A Kunin, in Russkaya Starina, 1870 Alexander Solodkoff, Orfèvrerie russe du XVIIe au XIXe siècle, 1981, A la Vieille Russie, The Art of the Goldsmith & the Jeweler, 1968, no. 174, illus. P. 76 Sidler, Catalogue officiel du Musée de l'Ariana, Genève, Ville de Genève / Atar, 1905. 234 p.. P. 126, n° 47 Eisler, William. The Dassiers of Geneva: 18th-century European medallists. Volume II: Dassier and sons: an artistic enterprise in Geneva and Europe, 1733-1759. Lausanne, 2005. Pp. 361– 362, fig. 47, repr. n/b Golay, Laurent. Alexandra Karouova et al.. Suisse-Russie. Des siècles d'amour et d'oubli, 1680- 2006. Lausanne, Musée historique de Lausanne. P. 55, repr. coul. Jeffares, Neil. Dictionary of pastellists before 1800. London, Unicorn Press, 2006. P. 622, non repr. Edition critique introduite et commentée du mémoire de Jérémie Pauzié, joaillier à la Cour de Russie de 1730 à 1763 / Mélanie Draveny, Mémoire de licence dactyl. Lettres Genève, 2004

Billions of years ago, Earth’s magnetic field may have gotten a jump-start from a turbulent magma ocean swirling around the planet’s core. Our planet has generated its own magnetism for almost its entire history (SN: 1/28/19). But it’s never been clear how Earth created this magnetic field during the planet’s Archean Eon — an early geologic period roughly 2.5 billion to 4 billion years ago. Now, computer simulations suggest that a deep layer of molten rock-forming minerals known as silicates might have been the culprit. “There’s a few billion years of Earth’s history where it’s difficult to explain what was driving the magnetic field,” says Joseph O’Rourke, a planetary scientist at Arizona State University in Tempe who was not involved with this study. This new result, he says, is a “vital piece of the puzzle.” Today, Earth’s magnetism is likely generated in the planet’s outer core, a layer of liquid iron and nickel. Heat escaping from the solid inner core drives flows of fluid that create circulating electric currents in the outer core, turning Earth’s innards into a gigantic electromagnet. The outer core, however, is a fairly recent addition, appearing roughly a billion or so years ago, and ancient rocks preserve evidence of a planetwide magnetic field much earlier than that. So, some other mechanism must have been at work during Earth’s formative years. One candidate for Earth’s first go at a magnetic field is a sea of liquid rock hypothesized to once have surrounded the young planet’s nascent core. To see if this ocean of molten silicates is a viable option, Lars Stixrude, a geophysicist at UCLA, and colleagues developed computer simulations to estimate the electrical properties of silicates at extreme temperatures and pressures. The team found that, at pressures more than 10 million times Earth’s surface atmospheric pressure and temperatures comparable to those on the surface of the sun, silicates conduct electricity well enough to produce a planetwide magnetic field. The strength of that field, the team reports February 25 in Nature Communications, roughly matches measurements of fossil magnetic fields in rocks that are about 2 billion to 4 billion years old. Around the end of the Archean, the team suggests, the magma ocean would have cooled and solidified, possibly handing over magnetic field duties to an increasingly turbulent core. The study is “an extremely important step forward in understanding the history of Earth’s magnetic field,” O’Rourke says. What’s more, it might also be relevant to other worlds today. “It’s not just a curiosity of ancient history,” he says. Super-Earths, rocky planets a few times as massive as Earth, might retain enough internal heat to sustain a deep silicate ocean for much longer than our planet did. These planets are also the most common worlds found outside the solar system. The mechanism behind Earth’s early magnetic field, the team speculates, may therefore be operating in large rocky planets throughout the universe.

According to ancient and medieval science, aether (//), also spelled æther or ether and also called quintessence, is the material that fills the region of the universe above the terrestrial sphere. The concept of aether was used in several theories to explain several natural phenomena, such as the traveling of light and gravity. In the late 19th century, physicists postulated that aether permeated all throughout space, providing a medium through which light could travel in a vacuum, but evidence for the presence of such a medium was not found in the Michelson–Morley experiment, and this result has been interpreted as meaning that no such luminiferous aether exists. The word αἰθήρ (aithḗr) in Homeric Greek means "pure, fresh air" or "clear sky". In Greek mythology, it was thought to be the pure essence that the gods breathed, filling the space where they lived, analogous to the air breathed by mortals. It is also personified as a deity, Aether, the son of Erebus and Nyx in traditional Greek mythology. Aether is related to αἴθω "to incinerate", and intransitive "to burn, to shine" (related is the name Aithiopes (Ethiopians; see Aethiopia), meaning "people with a burnt (black) visage"). In Plato's Timaeus (58d) speaking about air, Plato mentions that "there is the most translucent kind which is called by the name of aether (αἰθήρ)" but otherwise he adopted the classical system of four elements. Aristotle, who had been Plato's student at the Akademia, agreed on this point with his former mentor, emphasizing additionally that fire has sometimes been mistaken for aether. However, in his Book On the Heavens he introduced a new "first" element to the system of the classical elements of Ionian philosophy. He noted that the four terrestrial classical elements were subject to change and naturally moved linearly. The first element however, located in the celestial regions and heavenly bodies, moved circularly and had none of the qualities the terrestrial classical elements had. It was neither hot nor cold, neither wet nor dry. With this addition the system of elements was extended to five and later commentators started referring to the new first one as the fifth and also called it aether, a word that Aristotle had not used. Aether did not follow Aristotelian physics either. Aether was also incapable of motion of quality or motion of quantity. Aether was only capable of local motion. Aether naturally moved in circles, and had no contrary, or unnatural, motion. Aristotle also noted that crystalline spheres made of aether held the celestial bodies. The idea of crystalline spheres and natural circular motion of aether led to Aristotle's explanation of the observed orbits of stars and planets in perfectly circular motion in crystalline aether. Medieval scholastic philosophers granted aether changes of density, in which the bodies of the planets were considered to be more dense than the medium which filled the rest of the universe. Robert Fludd stated that the aether was of the character that it was "subtler than light". Fludd cites the 3rd-century view of Plotinus, concerning the aether as penetrative and non-material. See also Arche. Quintessence is the Latinate name of the fifth element used by medieval alchemists for a medium similar or identical to that thought to make up the heavenly bodies. It was noted that there was very little presence of quintessence within the terrestrial sphere. Due to the low presence of quintessence, earth could be affected by what takes place within the heavenly bodies. This theory was developed in the 14th century text The testament of Lullius, attributed to Ramon Llull. The use of quintessence became popular within medieval alchemy. Quintessence stemmed from the medieval elemental system, which consisted of the four classical elements, and aether, or quintessence, in addition to two chemical elements representing metals: sulphur, "the stone which burns", which characterized the principle of combustibility, and mercury, which contained the idealized principle of metallic properties. This elemental system spread rapidly throughout all of Europe and became popular with alchemists, especially in medicinal alchemy. Medicinal alchemy then sought to isolate quintessence and incorporate it within medicine and elixirs. Due to quintessence's pure and heavenly quality, it was thought that through consumption one may rid oneself of any impurities or illnesses. In The book of Quintessence, a 15th-century English translation of a continental text, quintessence was used as a medicine for many of man's illnesses. A process given for the creation of quintessence is distillation of alcohol seven times. Over the years, the term quintessence has become synonymous with elixirs, medicinal alchemy, and the philosopher's stone itself. With the 18th century physics developments, physical models known as "aether theories" made use of a similar concept for the explanation of the propagation of electromagnetic and gravitational forces. As early as the 1670s, Newton used the idea of aether to help match observations to strict mechanical rules of his physics. However, the early modern aether had little in common with the aether of classical elements from which the name was borrowed. These aether theories are considered to be scientifically obsolete, as the development of special relativity showed that Maxwell's equations do not require the aether for the transmission of these forces. However, Einstein himself noted that his own model which replaced these theories could itself be thought of as an aether, as it implied that the empty space between objects had its own physical properties. Despite the early modern aether models being superseded by general relativity, occasionally some physicists have attempted to reintroduce the concept of aether in an attempt to address perceived deficiencies in current physical models. One proposed model of dark energy has been named "quintessence" by its proponents, in honor of the classical element. This idea relates to the hypothetical form of dark energy postulated as an explanation of observations of an accelerating universe. It has also been called a fifth fundamental force. Aether and light The motion of light was a long-standing investigation in physics for hundreds of years before the 20th century. The use of aether to describe this motion was popular during the 17th and 18th centuries, including a theory proposed by Johann II Bernoulli, who was recognized in 1736 with the prize of the French Academy. In his theory, all space is permeated by aether containing "excessively small whirlpools". These whirlpools allow for aether to have a certain elasticity, transmitting vibrations from the corpuscular packets of light as they travel through. This theory of luminiferous aether would influence the wave theory of light proposed by Christiaan Huygens, in which light traveled in the form of longitudinal waves via an "omnipresent, perfectly elastic medium having zero density, called aether". At the time, it was thought that in order for light to travel through a vacuum, there must have been a medium filling the void through which it could propagate, as sound through air or ripples in a pool. Later, when it was proved that the nature of light wave is transverse instead of longitudinal, Huygens' theory was replaced by subsequent theories proposed by Maxwell, Einstein and de Broglie, which rejected the existence and necessity of aether to explain the various optical phenomena. These theories were supported by the results of the Michelson–Morley experiment in which evidence for the motion of aether was conclusively absent. The results of the experiment influenced many physicists of the time and contributed to the eventual development of Einstein's theory of special relativity. Aether and gravitation Aether has been used in various gravitational theories as a medium to help explain gravitation and what causes it. Few years later, aether was used in one of Sir Isaac Newton's first published theories of gravitation, Philosophiæ Naturalis Principia Mathematica (the Principia, 1687). He based the whole description of planetary motions on a theoretical law of dynamic interactions. He renounced standing attempts at accounting for this particular form of interaction between distant bodies by introducing a mechanism of propagation through an intervening medium. He calls this intervening medium aether. In his aether model, Newton describes aether as a medium that "flows" continually downward toward the Earth's surface and is partially absorbed and partially diffused. This "circulation" of aether is what he associated the force of gravity with to help explain the action of gravity in a non-mechanical fashion. This theory described different aether densities, creating an aether density gradient. His theory also explains that aether was dense within objects and rare without them. As particles of denser aether interacted with the rare aether they were attracted back to the dense aether much like cooling vapors of water are attracted back to each other to form water. In the Principia he attempts to explain the elasticity and movement of aether by relating aether to his static model of fluids. This elastic interaction is what caused the pull of gravity to take place, according to this early theory, and allowed an explanation for action at a distance instead of action through direct contact. Newton also explained this changing rarity and density of aether in his letter to Robert Boyle in 1679. He illustrated aether and its field around objects in this letter as well and used this as a way to inform Robert Boyle about his theory. Although Newton eventually changed his theory of gravitation to one involving force and the laws of motion, his starting point for the modern understanding and explanation of gravity came from his original aether model on gravitation.[self-published source?] - Celestial spheres - Dark matter - Energy (esotericism) - Etheric body - Etheric force - Etheric plane - Radiant energy - George Smoot III. "Aristotle's Physics". lbl.gov. Archived from the original on 20 December 2016. Retrieved 20 December 2016. - Carl S. Helrich, The Classical Theory of Fields: Electromagnetism Berlin, Springer 2012, p. 26. - "Aether". GreekMythology.com. Archived from the original on 20 December 2016. Retrieved 20 December 2016. - "AITHER". AETHER : Greek protogenos god of upper air & light ; mythology : AITHER. Retrieved January 16, 2016. - Pokorny, Julius (1959). Indogermanisches etymologisches Wörterbuch, s.v. ai-dh-. - Αἰθίοψ in Liddell, Scott, A Greek–English Lexicon: "Αἰθίοψ , οπος, ὁ, fem. Αἰθιοπίς , ίδος, ἡ (Αἰθίοψ as fem., A.Fr.328, 329): pl. 'Αἰθιοπῆες' Il.1.423, whence nom. 'Αἰθιοπεύς' Call.Del.208: (αἴθω, ὄψ):— properly, Burnt-face, i.e. Ethiopian, negro, Hom., etc.; prov., Αἰθίοπα σμήχειν 'to wash a blackamoor white', Luc.Ind. 28." Cf. Etymologicum Genuinum s.v. Αἰθίοψ, Etymologicum Gudianum s.v.v. Αἰθίοψ. "Αἰθίοψ". Etymologicum Magnum (in Greek). Leipzig. 1818. - Fage, John (2013-10-23). A History of Africa. Routledge. pp. 25–26. ISBN 978-1317797272. Retrieved 20 January 2015. ...[Africa's Indian Ocean] coast was called Azania, and no 'Ethiopeans', dark skinned people, were mentioned amongst its inhabitants. - Plato, Timaeus 58d. - Hahm, David E. (1982). "The fifth element in Aristotle's De Philosophia: A Critical Re-Examination". The Journal of Hellenic Studies. 102: 60–74. doi:10.2307/631126. JSTOR 631126. - G. E. R. Lloyd), Aristotle: The Growth and Structure of his Thought, Cambridge: Cambridge Univ. Pr., 1968, pp. 133-139, ISBN 0-521-09456-9. - Grant, Edward (1996). Planets, Stars, & Orbs: The Medieval Cosmos, 1200-1687 (1st pbk. ed.). Cambridge [England]: Cambridge University Press. pp. 322–428. ISBN 978-0-521-56509-7. - Robert Fludd, "Mosaical Philosophy". London, Humphrey Moseley, 1659. Pg 221. - The Alchemists, by F. Sherwood Taylor page 95 - The book of Quintessence Archived 2015-09-24 at the Wayback Machine, Early English Text society original series number 16, edited by F. J. Furnivall - The Dictionary of Alchemy, by Mark Haeffner - Margaret Osler, Reconfiguring the World. The Johns Hopkins University Press 2010. (155). - Einstein, Albert: "Ether and the Theory of Relativity" (1920), republished in Sidelights on Relativity (Methuen, London, 1922) - Dirac, Paul (1951). "Is there an Aether?". Nature. 168 (4282): 906–907. Bibcode:1951Natur.168..906D. doi:10.1038/168906a0. - Zlatev, I.; Wang, L.; Steinhardt, P. (1999). "Quintessence, Cosmic Coincidence, and the Cosmological Constant". Physical Review Letters (Submitted manuscript). 82 (5): 896–899. arXiv:astro-ph/9807002. Bibcode:1999PhRvL..82..896Z. doi:10.1103/PhysRevLett.82.896. - Whittaker, Edmund Taylor, A History of the Theories of Aether and Electricity from the Age of Descartes to the Close of the 19th Century (1910), pp. 101-02. - Michelson, Albert A. (1881). "The Relative Motion of the Earth and the Luminiferous Ether" (PDF). American Journal of Science. 22 (128): 120–129. Bibcode:1881AmJS...22..120M. doi:10.2475/ajs.s3-22.128.120. - Shankland, R. S. (1964). "Michelson-Morley Experiment". American Journal of Physics. 32 (1): 16. Bibcode:1964AmJPh..32...16S. doi:10.1119/1.1970063. - Rosenfeld, L. (1969). "Newton's views on aether and gravitation". Archive for History of Exact Sciences. 6 (1): 29–37. doi:10.1007/BF00327261. - Newton, Isaac."Isaac Newton to Robert Boyle, 1679." 28 February 1679. - James DeMeo (2009). "Isaac Newton's Letter to Robert Boyle, on the Cosmic Ether of Space - 1679". orgonelab.org. Archived from the original on 20 December 2016. Retrieved 20 December 2016. - Andrew Robishaw (9 April 2015). The Esoteric Codex: Esoteric Cosmology. Lulu.com. p. 6. ISBN 9781329053083. Retrieved 20 December 2016.[self-published source]

Be the first pioneers to continue the Astronomy Discussions at our new Astronomy meeting place... The Space and Astronomy Agora |What I Found Forum List | Follow Ups | Post Message | Back to Thread Topics | In Response To Posted by Jessica Lynn on January 22, 2000 15:29:09 UTC : : 1. What is a black hole? A black hole is defined by the escape velocity that would have to be attained to escape from the gravitational pull exerted upon an object. For example, the escape velocity of earth is equal to 11 km/s. Anything that wants to escape earth's gravitational pull must go at least 11 km/s, no matter what the thing is — a rocket ship or a baseball. The escape velocity of an object depends on how compact it is; that is, the ratio of its mass to radius. A black hole is an object so compact that, within a certain distance of it, even the speed of light is not fast enough to escape. | | 2. How is a black hole created? A common type of black hole is the type produced by some dying stars. A star with a mass of about 10 - 20 times the mass of our Sun may produce a black hole at the end of its life. In the normal life of a star there is a constant tug of war between gravity pulling in and pressure pushing out. Nuclear reactions in the core of the star produce enough energy to push outward. For most of a star's life, gravity and pressure balance each other exactly, and so the star is stable. However, when a star runs out of nuclear fuel, gravity gets the upper hand and the material in the core is compressed even further. The more massive the core of the star, the greater the force of gravity that compresses the material, collapsing it under its own weight. For small stars, when the nuclear fuel is exhausted and there are no more nuclear reactions to fight gravity, the repulsive forces among electrons within the star eventually create enough pressure to halt further gravitational collapse. The star then cools and dies peacefully. This type of star is called the "white dwarf." When a very massive star exhausts its nuclear fuel it explodes as a supernova. The outer parts of the star are expelled violently into space, while the core completely collapses under its own weight. To create a massive core a progenitor (ancestral) star would need to be 10 - 20 times more massive than our Sun. If the core is very massive (approximately 2.5 times more massive than the Sun), no known repulsive force inside a star can push back hard enough to prevent gravity from completely collapsing the core into a black hole. Then the core compacts into a mathematical point with virtually zero volume, where it is said to have infinite density. This is referred to as a singularity. When this happens, escape would require a velocity greater than the speed of light. No object can reach the speed of light. The distance from the black hole at which the escape velocity is just equal to the speed of light is called the event horizon. Anything, including light, that passes across the event horizon toward the black hole is forever trapped. | | 3. Since light has no mass how can it be trapped by the gravitational pull of a black hole? Newton thought that only objects with mass could produce a gravitational force on each other. Applying Newton's theory of gravity, one would conclude that since light has no mass, the force of gravity couldn't affect it. Einstein discovered that the situation is a bit more complicated than that. First he discovered that gravity is produced by a curved space-time. Then Einstein theorized that the mass and radius of an object (its compactness) actually curves space-time. Mass is linked to space in a way that physicists today still do not completely understand. However, we know that the stronger the gravitational field of an object, the more the space around the object is curved. In other words, straight lines are no longer straight if exposed to a strong gravitational field; instead, they are curved. Since light ordinarily travels on a straight-line path, light follows a curved path if it passes through a strong gravitational field. This is what is meant by "curved space," and this is why light becomes trapped in a black hole. In the 1920's Sir Arthur Eddington proved Einstein's theory when he observed starlight curve when it traveled close to the Sun. This was the first successful prediction of Einstein's General Theory of Relativity. One way to picture this effect of gravity is to imagine a piece of rubber sheeting stretched out. Imagine that you put a heavy ball in the center of the sheet. The weight of the ball will bend the surface of the sheet close to it. This is a two-dimensional picture of what gravity does to space in three dimensions. Now take a little marble and send it rolling from one side of the rubber sheet to the other. Instead of the marble taking a straight path to the other side of the sheet, it will follow the contour of the sheet that is curved by the weight of the ball in the center. This is similar to how the gravitation field created by an object (the ball) affects light (the marble). 4. What does a black hole look like? A black hole itself is invisible because no light can escape from it. In fact, when black holes were first hypothesized they were called "invisible stars." If black holes are invisible, how do we know they exist? This is exactly why it is so difficult to find a black hole in space! However, a black hole can be found indirectly by observing its effect on the stars and gas close to it. For example, consider a double-star system in which the stars are very close. If one of the stars explodes as a supernova and creates a black hole, gas and dust from the companion star might be pulled toward the black hole if the companion wanders too close. In that case, the gas and dust are pulled toward the black hole and begin to orbit around the event horizon and then orbit the black hole. The gas becomes heavily compressed and the friction that develops among the atoms converts the kinetic energy of the gas and dust into heat, and x-rays are emitted. Using the radiation coming from the orbiting material, scientists can measure its heat and speed. From the motion and heat of the circulating matter, we can infer the presence of a black hole. The hot matter swirling near the event horizon of a black hole is called an accretion disk. John Wheeler, a prominent theorist, compared observing these double-star systems to watching women in white dresses dancing with men in black tuxedos within a dimly lit ballroom. You see only the women, but you could predict the existence of their invisible partners because of the women's' spinning and whirling motions around a central axis. Searching for stars whose motions are influenced by invisible partners is one way in which astronomers search for possible black holes. | | 5. Is a black hole a giant cosmic vacuum cleaner? The answer to this question is "not really." To understand this, first consider why the force of gravity is so strong close to a black hole. The gravity of a black hole is not special. It does not attract matter differently than any other object does. At a long distance from the black hole the force of gravity falls off as the inverse square of the distance, just as it does for normal objects. Mathematically, the gravity of any spherical object behaves as if all the mass were concentrated at one central point. Since most ordinary objects have surfaces, you will feel the strongest gravity of an object when you are on its surface. This is as close to its total mass as you can get. If you penetrated the spherical object, getting closer to its core, you would feel the force of gravity get weaker, not stronger. The force of gravity you feel depends on the mass that is interior to you, because the gravity from the mass behind you is exactly canceled by the mass in the opposite direction. Therefore, you will feel the strongest force of gravity from an object, for example a planet, when you are standing on the planet's surface, because it is on the surface that you are closest to its total mass. Penetrating the surface of the planet does not expose you to more of the planet's total mass, but actually exposes you to less of its mass. Now remember the size of a black hole is infinitesimally small. Gravity near a black hole is very strong because objects can get extremely close to it and still be exposed to its total mass. There is nothing special about the mass of a black hole. A black hole is different from our ordinary experience not because of its mass, but because its radius has vanished. Far away from the black hole, you would feel the same strength of gravity as if the black hole were a normal star. But the force of gravity close to a black hole is enormously strong because you can get so close to its total mass! For example, the surface of the Earth where we are standing is 6378 km from the center of the Earth. The surface is as close as you can get and still be exposed to the total mass of the Earth. Thus, it is where you will feel the strongest gravity. If suddenly the Earth became a black hole (impossible!) and you remained at 6378 km from the new Earth-black hole, you would feel the same pull of gravity as you do today. For example, if you normally weigh 120 lbs, you would still weigh 120 lbs. The mass of the Earth hasn't changed, your distance from it hasn't changed, and therefore you would experience the same gravitational force as you feel on the surface of normal Earth. But with the Earth-black hole, it would be possible for you to get closer to the total mass of the Earth. Let's say that you weigh 120 lbs standing on the surface of normal Earth. As you venture closer toward the Earth-black hole you would feel a stronger and stronger force. If you went to within 3189 km of the Earth-black hole you would weigh 480 lbs! For the same exercise with the Earth as we normally experience it, if you dug your way to 3189 km of the center, you would weigh less than at the surface, a mere 60 lbs, because there would be less Earth mass interior relative to you! As another example, consider the Sun. If the Sun suddenly became a black hole (equally impossible!), the Earth would continue on its normal orbit and would feel the same force of gravity from the Sun as usual! Therefore, to be "sucked up" by a black hole, you have to get very close; otherwise, you experience the same force of gravity as if the black hole were the normal star it used to be. As you get close to a black hole, relativistic effects become important; for example, the escape velocity approximates and eventually reaches the speed of light and some very strange things like the "event horizon effect" begin to happen. For details, consult any popular book on black holes. | | 6. Do all stars become black holes? Only stars with very large masses can become black holes. Our Sun, for example, is not massive enough to become a black hole. Four billion years from now when the Sun runs out of the available nuclear fuel in its core, our Sun will die a quiet death. Stars of this type end their history as white dwarf stars. More massive stars, such as those with masses of 10 - 20 times our Sun's mass, may eventually create a black hole. When a massive star runs out of nuclear fuel it can no longer sustain its own weight and begins to collapse. When this occurs the star heats up and some fraction of its outer layer, which often still contains some fresh nuclear fuel, activates the nuclear reaction again and explodes in what is called a supernova. The remaining innermost fraction of the star, the core, continues to collapse. Depending on how massive the core is, it may become either a neutron star and stop the collapse or it may continue to collapse into a black hole. The dividing mass of the core, which determines its fate, is about 2.5 solar masses. It is thought that to produce a core of 2.5 solar masses the ancestral star should begin with about 10 - 20 solar masses. A black hole formed from a star is called a stellar black hole. | | 7. How many types of black holes are there? According to theory, there might be three types of black holes: stellar, supermassive, and miniature black holes — depending on their size. These black holes have also formed in different ways. Stellar black holes are described in Question 6. Supermassive black holes likely exist in the centers of most galaxies, including our own galaxy, the Milky Way. They can have a mass equivalent to billions of suns. In the outer parts of galaxies (where our solar system is located within the Milky Way) there are vast distances between stars. However, in the central region of galaxies, stars are packed very closely together. Because everything in the central region is tightly packed to start with, a black hole in the center of a galaxy can become more and more massive as stars orbiting the event horizon can ultimately be captured by gravitational attraction and add their mass to the black hole. By measuring the velocity of stars orbiting close to the center of a galaxy, we can infer the presence of a supermassive black hole and calculate its mass. Perpendicular to the accretion disk of a supermassive black hole, there are sometimes two jets of hot gas. These jets can be millions of light years in length. They are probably caused by the interaction of gas particles with strong, rotating magnetic fields surrounding the black hole. Observations with the Hubble Space Telescope have provided the best evidence to date that supermassive black holes exist. The exact mechanisms that result in what are known as miniature black holes have not been precisely identified, but a number of hypotheses have been proposed. The basic idea is that miniature black holes might have been formed shortly after the "Big Bang," which is thought to have started the Universe about 15 billion years ago. Very early in the life of the Universe the rapid expansion of some matter might have compressed slower-moving matter enough to contract into black holes. Some scientists hypothesize that black holes can theoretically "evaporate" and explode. The time required for the "evaporation" would depend upon the mass of the black hole. Very massive black holes would need a time that is longer than the current accepted age of the universe. Only miniature black holes are thought to be capable of evaporation within the existing time of our universe. For a black hole formed at the time of the "Big Bang" to evaporate today its mass must be about 1015g (i.e., about 2 million pounds), about twice the mass of the current Homo sapien population on planet Earth. During the final phase of the "evaporation," such a black hole would explode with a force of several trillion times that of our most powerful nuclear weapon. So far, however, there is no observational evidence for miniature black holes. | | 8. When were black holes first theorized? Using Newton's Laws in the late 1790s, John Michell of England and Pierre LaPlace of France independently suggested the existence of an "invisible star." Michell and LaPlace calculated the mass and size — which is now called the "event horizon" — that an object needs in order to have an escape velocity greater than the speed of light. In 1967 John Wheeler, an American theoretical physicist, applied the term "black hole" to these collapsed objects. | | 9. What evidence do we have for the existence of black holes? Astronomers have found convincing evidence for a supermassive black hole in the center of the giant elliptical galaxy M87, as well as in several other galaxies. The discovery is based on velocity measurements of a whirlpool of hot gas orbiting the black hole. Hubble Space Telescope data produced an unprecedented measurement of the mass of an unseen object at the center of the galaxy. Based on the kinetic energy of the material whirling about the center (as in Wheeler's dance, see Question 4 above), the object is about 3 billion times the mass of our Sun and appears to be concentrated into a space smaller than our solar system. For many years x-ray emission from the double-star system Cygnus X-1 convinced many astronomers that the system contains a black hole. With more precise measurements available recently, the evidence for a black hole in Cygnus X-1 is very strong. | | 10. How does the Hubble Space Telescope search for black holes? A black hole cannot be viewed directly because light cannot escape it. Effects on the matter that surrounds it infer its presence. Matter swirling around a black hole heats up and emits radiation that can be detected. Around a stellar black hole this matter is composed of gas and dust. Around a supermassive black hole in the center of a galaxy the swirling disk is made of not only gas but also stars. An instrument aboard the Hubble Space Telescope, called the Space Telescope Imaging Spectrograph (STIS), was installed in February 1997. STIS is the space telescope's main "black hole hunter." A spectrograph uses prisms or diffraction gratings to split the incoming light into its rainbow pattern. The position and strength of the line in a spectrum gives scientists valuable information. STIS spans ultraviolet, visible, and near-infrared wavelengths. This instrument can take a spectrum of many places at once across the center of a galaxy. Each spectrum tells scientists how fast the stars and gas are swirling at that location. With that information, the central mass that the stars are orbiting can be calculated. The faster the stars go, the more massive the central object must be. STIS found the signature of a supermassive black hole in the center of the galaxy M84. The spectra showed a rotation velocity of 400 km/s, equivalent to 1.4 million km every hour! The Earth orbits our Sun at 30 km/s. If Earth moved as fast as 400 km/s our year would be only 27 days long! | | A few words from the scientist: When we got together last summer it was a particularly exciting time to be creating a lesson about black holes. A new instrument on HST had just become the ideal science instrument to find and study supermassive black holes that reside in the center of galaxies. Among the remarkable things HST can accomplish with this instrument, the Imaging Spectrograph (STIS), will be a black hole survey. STIS is something like a "Cosmic Speed Gun" - when Hubble is pointed at a galaxy it can determine the speed of material that circulates the galactic center. The faster stuff moves around the center, the more massive that center must be. With high-school-level physics we can determine the mass of these supermassive black holes. Just as we know the mass of our Sun by observing the planets in their orbits about the Sun, we will know the mass of the black holes that reside in the center of each and every galaxy in which we point the STIS "speedgun." The real STIS image of the central region of galaxy M84 is used in the "Amazing Space Black Hole Activity." As more STIS results accumulate, it seems that many, if not most, galaxies have supermassive black holes at their center. In my research I have studied gravity on a much smaller scale. I use the circulation of our oceans and atmosphere to test how this motion affects the gravitational field of the earth. For example, satellites orbiting the Earth exhibit measurable changes in their orbits as a result of El Niño. In fact, when you get up and leave the computer terminal you will be changing the Earth's gravitational field by a very small amount. Of course, your walking across the room is not measurable from space. However, it would be an interesting experiment to see how many teachers would have to get up and walk across their rooms to cause a measurable change in the Earth's gravitational field. The gravitational phenomena that occur on Earth and in our solar system are many times smaller in magnitude and scale and not nearly as bizarre as those that occur in and around a black hole. I hope that the activities developed in this lesson plan will capture students' imagination, provide them with a better understanding of our universe, and let them have fun all at the same time. Daniel Steinberg Unless otherwise specified, web site content Copyright 1994-2020 John Huggins All Rights Reserved Forum posts are Copyright their authors as specified in the heading above the post. "dbHTML," "AstroGuide," "ASTRONOMY.NET" & "VA.NET" are trademarks of John Huggins

The NASA Chromospheric Layer Spectropolarimeter-2 ,or CLASP-2 sounding rocket mission, was successfully conducted on April 11 from the White Sands Missile Range in New Mexico, launched aboard a NASA Black Brant IX sounding rocket at 12:51 p.m. EDT — the CLASP-2 payload flew to an altitude of 170 miles before descending by parachute. The payload was recovered and is reported in good condition. Good data was received and the science team is reported to be happy with the results of the mission. CLASP-2, the acronym for Chromospheric Layer Spectropolarimeter-2, is a sounding rocket mission. Smaller, more affordable and faster to design and build than large-scale satellite missions, sounding rockets offer a way for the team to test their latest ideas and instruments — and achieve rapid science results. The CLASP-2 instrument uses ultraviolet light to look for hidden details in a complex region of the Sun's atmosphere called the chromosphere. Scientists hope that CLASP-2 experiment will help unlock new clues about how the Sun's energy travels up through the layers of its atmosphere, and eventually out into space. The Sun was observed for about five minutes and images were captured, as well as polarization spectra — observations that restrict incoming light to a specific direction and then record the intensity of individual wavelengths of ultraviolet light. The NASA team's focus was on obtaining polarization measurements that have never before gathered at these ultraviolet wavelengths. CLASP-2 is a follow-on mission to the Chromospheric Lyman-Alpha Spectro-Polarimeter, which offered the first-ever polarization measurements of ultraviolet light emitted from the sun's chromosphere. Previous polarization measurements were restricted to visible and infrared light emitted from other regions of the Sun’s atmosphere. Polarization measurements are important as they provide information on the strength and direction of the Sun's magnetic field, which plays a central role in sculpting the solar atmosphere. Understanding how the magnetic field works is vital to predicting powerful solar activity and protecting space and Earth technology from potential damage from geomagnetic storms. On the ground, researchers will use advanced computer modeling to interpret the data collected by CLASP-2 and better understand how the energy moves through the chromosphere. And even as CLASP-2 uncovers new information, scientists working with its data will rely on data from other observatories to help put those details in context. CLASP-2's launch and data collection will be coordinated with two satellites: NASA's Interface Region Imaging Spectrograph, or IRIS--a satellite observatory that captures non-polarized spectra and images of the Sun’s atmosphere--and the joint JAXA/NASA Hinode satellite observatory, making magnetic measurements at the Sun’s surface as well as images and spectroscopy in the much hotter atmospheric layer known as the corona. Also taking coordinated data are the Dunn Solar Telescope in Sunspot, New Mexico, and the Goode Solar Telescope in Big Bear, California. CLASP-2 is an international collaboration led by NASA's Marshall Space Flight Center with contributions from Japan, Spain and France. CLASP-2 is supported through NASA’s Sounding Rocket Program at the agency’s Wallops Flight Facility in Virginia. NASA’s Heliophysics Division manages the sounding rocket program.

In just over one weeks time, Mercury will pass in front of the Sun. Although Mercury only covers 0.004% of the surface of the Sun, this is a rare event and hence worthwhile to have a closer look at, although you should, of course, never “look” at the Sun directly without proper protection. As only one of three bodies in the solar system (this is ignoring a vast number of tiny rocks and asteroids orbiting the sun in an orbit smaller than Earths orbit), Mercury is able to pass in front of the Sun. But while the Moon treats us with a (partial or total) solar eclipse, and Venus presents itself as a well visible black dot during a venus transit, Mercury is farthest away from the Earth and is hence fairly smal. Here is an image of the last Transit of Mercury in 2003: The image was recorded using a 90mm maksutov telescope with 1250mm focal length on slide film. Graphical illustration of the transit. With a well protected telescope, one can see Mercury starting to nibble at the sun at 13:12h CEST for about three minutes, after which the whole of Mercury is visible in front of the sun. At 16:56h CEST Mercury is closest to the center of the Sun and heads again for the rim, which he will reach at 20:37h and after another three minutes, at 20:40h, Mercury will have left the disk of the Sun. At that time, the Sun almost sets in Aachen, but is still three degrees above the horizon. For exact times, CalSky is a very good tool to do the calculations. Due to the tiny diameter of Mercury, the transit is not visible to the (well protected) naked eye. If you do not have the proper equipment to pbserve the transit yourself, there are many events in and around Germany where you can enjoy the transit under professional assistance. And of course, there will be an event at the Sternwarte Aachen. If everything fails, there are some livestreams, e.g. at the Peterberg in the Saarland or, possibly the safest option regarding weather, the NASA stream with images of the solar observatory SDO: http://mercurytransit.gsfc.nasa.gov. Fingers crossed for perfect weather like in 2003, when the transit was perfectly visible here in Aachen. EDIT: Here is another list with observations in the German area: and for the rest of the world:

The next NASA mission to Mars, the InSight lander, will include some additional experimental technology: the first deep-space CubeSats. Two small CubeSats will fly past the planet as the lander is descending through the atmosphere; this will be the first time CubeSats have been used in an interplanetary mission. If all goes well, the technology will provide NASA with a new way to quickly transmit status information about the main spacecraft after it lands on Mars. The twin CubeSats will be known together as Mars Cube One (MarCO), and are being built by NASA’s Jet Propulsion Laboratory (JPL). CubeSats are basically smaller versions of traditional satellites, using off-the-shelf technologies. Dozens have already been launched into Earth orbit and many have been designed by university students. A basic CubeSat is a box roughly 4 inches (10 centimeters) square, with larger CubeSats being multiples of that unit. MarCO’s design is a six-unit CubeSat—about the size of a briefcase – with a stowed size of about 36.6 centimetres (14.4 inches) by 24.3 centimetres (9.5 inches) by 11.8 centimetres (4.6 inches). MarCO will launch from Vandenberg Air Force Base, Calif., on the same United Launch Alliance Atlas V rocket as the Interior Exploration using Seismic Investigations, Geodesy and Heat Transport (InSight) lander, in March 2016. After launch, the two CubeSats will separate from the Atlas V booster and travel independently to Mars. They will then deploy two radio antennas and two solar panels. The high-gain, X-band antenna will direct radio waves the same way that a parabolic dish antenna does. “MarCO is an experimental capability that has been added to the InSight mission, but is not needed for mission success,” said Jim Green, director of NASA’s planetary science division at the agency’s headquarters in Washington. “MarCO will fly independently to Mars.” While InSight is descending through the Martian atmosphere on Sep. 28, 2016, it will also relay information in the UHF radio band to the Mars Reconnaissance Orbiter (MRO), which will then forward it back to Earth. One downside, however, is that MRO cannot simultaneously receive information over one band while transmitting on another, which means that confirmation of a successful landing might be received by the orbiter an hour before it is transmitted to Earth. MarCO could nicely solve that problem, as its softball-sized radio provides both UHF (receive only) and X-band (receive and transmit) functions capable of immediately relaying information received over UHF. As previously reported, NASA has already started testing of the InSight lander at the Lockheed Martin Space Systems facility near Denver, Colo. According to Stu Spath, InSight program manager at Lockheed Martin Space Systems in Denver: “The assembly of InSight went very well and now it’s time to see how it performs. The environmental testing regimen is designed to wring out any issues with the spacecraft so we can resolve them while it’s here on Earth. This phase takes nearly as long as assembly, but we want to make sure we deliver a vehicle to NASA that will perform as expected in extreme environments.” “It’s great to see the spacecraft put together in its launch configuration,” said InSight Project Manager Tom Hoffman at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, Calif. “Many teams from across the globe have worked long hours to get their elements of the system delivered for these tests. There still remains much work to do before we are ready for launch, but it is fantastic to get to this critical milestone.” Future versions of MarsCO could be used as a “bring-your-own” communications relay option for use by future Mars missions in the critical few minutes between Martian atmospheric entry and touchdown. They might even be used later for other planetary missions, and could be incorporated into newer mission technologies such as LightSail, which just this week successfully completed a low-Earth orbit test of deploying its solar sails, despite a few glitches. LightSail itself is a CubeSat spacecraft which is designed to use solar sailing technology, using energy from the Sun as propulsion, as a means of traveling through the Solar System. Such missions could be a reliable yet less expensive way to explore the outer Solar System as apposed to conventional rockets. In related Mars news, the newest Mars orbiter, MAVEN, recently took ultraviolet images of auroras in the Martian atmosphere. “It really is amazing,” said Nick Schneider who leads MAVEN’s Imaging Ultraviolet Spectrograph (IUVS) instrument team at the University of Colorado. “Auroras on Mars appear to be more wide-ranging than we ever imagined.” Known as “Christmas lights” by researchers, the auroras “circled the globe and descended so close to the Martian equator that, if the lights had occurred on Earth, they would have been over places like Florida and Texas.” Instead of a global magnetic field like Earth has, Mars’ disjointed magnetic fields sprout out of the ground like mushrooms, mostly in the southern hemisphere. They are thought to be the remains of a global magnetic field which did exist previously but has long since mostly decayed. The Mars Reconnaissance Orbiter had also recently detected impact glass on Mars for the first time, which may also offer additional clues to the possibility of past life. On Earth, impact glass has been found to contain organic material from previously living microbes and even bits of plants. Both of the Mars rovers, Curiosity and Opportunity, as well as the orbiters, are currently still waiting out the Mars solar conjunction, where Mars passes almost directly behind the Sun from Earth’s perspective, temporarily cutting off communications with rovers and orbiters (this time from June 7 to June 21). Curiosity is sitting in Marias Pass and Opportunity at the entrance to Marathon Valley while they wait for the conjunction period to end. Curiosity also recently received an upgrade to its Chemistry and Camera (ChemCam) instrument, which provides information about the chemical composition of targets by zapping them with laser pulses and taking spectrometer readings of the induced sparks, as well as taking detailed images through a telescope. This article was first published on AmericaSpace.

As intelligent as we are, as human’s we aren’t endowed with the most powerful of eyes. Sure, most of us can see the full glory of the ROYGBIV rainbow, but, it requires special devices for us to perceive specific frequencies of the electromagnetic spectrum. Indeed, perception plays a big part of the entire equation. As humans, we can only tell our narrative from our own point of view. Mystical as the celestial bodies may be, some of the most wondrous things can actually be explained by once you factor in our limitations. While the Moon certainly appears to change color during certain moments of the year, in truth, nothing much changes on the moon, it’s always the same color. So what makes the color of the Moon appear to change? Well, turns out it’s actually a combination of two things, our viewing angle paired with the composition of Earth’s atmosphere. To travel around the Earth, the Moon takes about a month. As it moves about the Earth, you need to also remember that Earth is not stationary, rather, it’s spinning on its axis. Importantly, the Earth and Moon are always in orbit around the sun. With this in mind, it’s clear to see why the Moon usually has a different route through the sky each night. When the Moon is hanging really low in the sky i.e. close to the horizon, you may have noticed that it appears to be brilliantly orange. If you’ve ever been curious about what causes this, then, you’ll be glad to know it’s because you’re viewing the Moon through much more of Earth’s atmosphere than when the Moon is up there in the sky. As mentioned earlier, the Earth is beautifully made. Our home planet’s atmosphere consists of a sphere of gases. When you’re viewing the Moon when it straight above the Earth, you’re actually looking through a thin band of the atmosphere. On the other hand, when you’re viewing the Moon when it’s close to the horizon, you’re viewing through a thicker layer of Earth’s atmosphere. Since Earth’s atmosphere consists of a plethora of airborne particles that absorb and scatter light, shorter wavelength’s of light are likely to be more scattered than longer wavelengths. On the flip side, blue light consists of shorter wavelengths, therefore, this kind of light easily get scattered. Given this background, it’s perfectly understandable why both the Sun and the Moon appear red when rising or setting. Since these are usually moments when the celestial bodies are near the horizon, your eyes are only able to perceive them once the light from them goes through the max amount of atmospheric exposure. As a natural satellite, the Moon does not produce any light of its own. Instead, it’s fully dependent on the Sun to provide light. When total lunar eclipses occur (i.e. when the Earth is situated between the Sun and the Moon), the Moon adapts a reddish hue since there’s almost zero sunlight hitting the lunar surface. This Red Moon happening is at times referred to as Blood Moon. While there are a ton of mythologies about this phenomenon, the reddish coloration is brought about by Rayleigh scattering. This is actually the same concept we covered earlier about how Earth’s atmospheric content (dust, moisture, and cloud levels), contribute towards the color of the Moon. The phrase “Once in a Blue Moon” is actually quite common. That said, the Moon rarely actually looks blue. From data, we know that Blue Moons happens every 3 years or so. Unique from the Red Moon scenario, Blue Moons can occur during any lunar phase. The Blue Moon hue emanates from increased dust or smoke particles in the atmosphere. Incidences like massive forest fires and volcanic eruptions occasionally trigger the emergence of the Blue Moon phenomenon. That wraps up our review on what makes the color of the Moon to change. We’re confident you’ve been able to pick up a thing or two about how the Blue Moon and Red Moon arise. The Moon has captivated the human imagination throughout history. Though it is ever-present, there is so little we know. We wanted to bring the Moon closer, to bring all of our stargazing dreams into reality. With the inspiration of holding the moon in your hands, AstroReality creates the most precisely made Moon model – LUNAR Pro, that satisfies your space curiosity. Besides the planetary models, AstroReality is bringing space to your everyday life, for you to experience the Moon in a brand new way. We designed and crafted the Moon Mug that gives you a sip of Moon together with the Moon Phase of tonight in Augmented Reality. Be one of the first to experience the Moon Mug by signing up our email newsletter today, and stay tuned with the latest updates from AstroReality.

NASA’s Juno probe arrived at Jupiter and performed orbital insertion on Independence Day in 2016 after a five-year journey from Earth. Shortly after orbital insertion, planetary observation commenced, and it continues to study the massive planet’s properties today. Juno is helping NASA learn more about Jupiter’s magnetic field, atmospheric composition & pressure, and more. Equipped with JunoCam, the probe has sent back countless high-detail images that peer into Jupiter’s chaotic clouds. Despite some initial issues with its onboard computer system and a few sticky engine valves, NASA improvised by keeping Juno in its current orbit. This makes collecting data a little slower than initially anticipated, but it still works for all the scientific observations that are planned. Image Credit: NASA/JPL-Caltech On Monday, June 10th, Juno came within viewing distance of the Great Red Spot, a massive storm that some researchers think has existed for centuries. NASA seized the opportunity to capture high-detail images of the Great Red Spot with JunoCam, which are expected to surface “in the coming days.” "For generations people from all over the world and all walks of life have marveled over the Great Red Spot," said Scott Bolton, principal investigator of Juno from the Southwest Research Institute in San Antonio. "Now we are finally going to see what this storm looks like up close and personal." Juno came within 5,600 miles of the cloud tops just above the Great Red Spot, which provided a bird’s-eye view of everything there is to see. While there, Juno’s instruments went on full alert, ready to capture raw data for astronomers to analyze. While many compare the Great Red Spot to a hurricane on Earth, its properties are actually very different. It rotates more quickly, it’s significantly larger, and has lasted longer without a water source than any Earthly hurricane. NASA says that this big storm is 1.3x the width of the Earth, spanning over 10,000 miles. It will be a waiting game until the images are processed, received, and released to the public. From the sound of things, it shouldn’t be long now before we get our first glimpse. These will be some of the most detailed images anyone has ever seen of the Great Red Spot to date, so we're just as excited as the rest of the world to see what Juno captured.

A large asteroid visits our fair corner of the solar system this week, and with a little planning you may just be able to spot it. Near Earth Asteroid (NEA) 285263 (1998 QE2) will pass 5.8 million kilometres from the Earth on Friday, May 31st at 20:59 Universal Time (UT) or 4:59PM EDT. Discovered in 1998 during the LIncoln Near-Earth Asteroid Research (LINEAR) sky survey looking for such objects, 1998 QE2 will shine at magnitude +10 to +12 on closest approach. Estimates of its size vary from 1.3 to 2.9 kilometres, with observations by the Spitzer Space Telescope in 2010 placing the ballpark figure towards the high end of the scale at 2.7 kilometres in diameter. 1998 QE2 would fit nicely with room to spare in Oregon’s 8 kilometre-wide Crater Lake. Though this passage is over 15 times as distant as the Earth’s Moon, the relative size of this space rock makes it of interest. This is the closest approach of 1998 QE2 for this century, and there are plans to study it with both the Arecibo and Goldstone radio telescopes to get a better description of its size and rotation as it sails by. Expect to see radar maps of 1998 QE2 by this weekend. “Asteroid 1998 QE2 will be an outstanding radar imaging target… we expect to obtain a series of high-resolution images that could reveal a wealth of surface features,” said astronomer and principal JPL investigator Lance Benner. An Amor-class asteroid, 1998 QE2 has an orbit of 3.77 years that takes it from the asteroid belt between Mars and Jupiter to just exterior of the Earth’s orbit. 1998 QE2 currently comes back around to our vicinity roughly every 15 years, completing about 4 orbits as it does so. Its perihelion exterior to our own makes it no threat to the Earth. This week’s passage is the closest for 1998 QE2 until a slightly closer pass on 0.038 Astronomical Units on May 27th, 2221. Note that on both years, the Earth is just over a month from aphelion (its farthest point from the Sun) which falls in early July. Of course, the “QE2” designation has resulted in the inevitable comparisons to the size of the asteroid in relation to the Queen Elizabeth II cruise liner. Asteroid designations are derived from the sequence in which they were discovered in a given year. 1998 QE2 was the 55th asteroid discovered in the period running from August 1st to 16th 1998. Perhaps we could start measuring asteroids in new and creative units, such as “Death Stars” or “Battlestars?” But the good news is, you can search for 1998 QE2 starting tonight. The asteroid is currently at +12th magnitude in the constellation Centaurus and will be cruising through Hydra on its way north into Libra Friday on May 31st. You’ll need a telescope to track the asteroid as it will never top +10th magnitude, which is the general threshold for binocular viewing under dark skies. Its relative southern declination at closest approach means that 1998 QE2 will be best observed from northern latitudes of +35° southward. The farther south you are, the higher it will be placed in the sky after dusk. Still, if you can spot the constellation Libra, it’s worth a try. Many observers in the southern U.S. fail to realize that southern hemisphere sites like Omega Centauri in the constellation Centaurus are visible in the evening low to the south at this time of year. Libra sits on the meridian at local midnight due south for northern hemisphere observers, making it a good time to try for the tiny asteroid. Visually, 1998 QE2 will look like a tiny, star-like point in the eye-piece of a telescope. Use low power and sketch or photograph the field of view and compare the positions of objects about 10 minutes apart. Has anything moved? We caught sight of asteroid 4179 Toutatis last year using this method. 1998 QE2 will also pass near some interesting objects that will serve as good “guideposts” to track its progress. We find the asteroid about 5° north of the bright +2.5 magnitude star Iota Centauri on the night of May 28th. It then crosses the border into the constellation Hydra about 6° south of the +3 magnitude star Gamma Hydrae (Star Trek fans will recall that this star lies in the Neutral Zone) on May 29th. Keep a careful eye on 1998 QE2 as it passes within 30’ (about the diameter of a Full Moon) of the +8th magnitude galaxy Messier 83 centered on May 28th at 19:00 UT/3:00 PM EDT. This will provide a fine opportunity to construct a stop-motion animated .gif of the asteroid passing by the galaxy. Another good opportunity to pinpoint the asteroid comes on the night on Thursday, May 30th as it passes within 30’ of the +3.3 magnitude star Pi Hydrae. From there, it’s on to closest approach day. 1998 QE2 crosses into the constellation Libra early on Friday May 31st. The Moon will be at Last Quarter phase and won’t rise until well past local midnight, aiding in your quest. At its closest approach, 1998 QE2 have an apparent motion of about 1 angular degree every 3 hours, or about 2/3rds the diameter of a Full Moon every hour. This isn’t quite fast enough to see in real time like asteroid 2012 DA14 was earlier this year, but you should notice its motion after about 10 minutes at medium power. Passing at ~465 Earth diameters distant, 1998 QE2 will show a maximum parallax displacement of just a little over 7 arc minutes at closest approach. For telescopes equipped with setting circles, knowing the asteroid’s precise position is crucial. This allows you to aim at a fixed position just ahead of its path and “ambush” it as it drifts by. For the most precise positions in right ascension and declination, be sure to check out JPL’s ephemeris generator for 1998 QE2. After its closest passage, 1998 QE2 will pass between the +3.3 & +2.7 magnitude stars Brachium (Sigma Librae) and Zubenelgenubi (Alpha Librae) around 4:00 UT on June 1st. Dedicated observers can continue to follow its northeastward trek into early June. Slooh will also be carrying the passage of 1998 QE2 on Friday, May 31st starting at 5:00 PM EDT/21:00 UT. Of course, the hypothetical impact of a space rock the size of 1998 QE2 would spell a very bad day for the Earth. The Chicxulub impact basin off of the Yucatán Peninsula was formed by a 10 kilometre impactor about 4 times larger than 1998 QE2 about 65 million years ago. We can be thankful that 1998 QE2 isn’t headed our way as we watch it drift silently by this week. Hey, unlike the dinosaurs, WE have a space program… perhaps, to paraphrase science fiction author Larry Niven, we can hear the asteroid whisper as we track its progress across the night sky, asking humanity “How’s that space program coming along?”