Long-lost, Dangerous Asteroid Is Found Again

ScienceDaily (Oct. 15, 2007) — Echoing the re-discovery of America by the Spanish long after an earlier Viking reconnaissance, astronomers have learned that a recently observed asteroid - one that could potentially hit the Earth - was actually first observed nearly a half-century ago. Researchers at the Minor Planet Center of the Smithsonian Astrophysical Observatory in Cambridge, MA have confirmed work by SETI Institute astronomer Peter Jenniskens that the recently discovered asteroid 2007 RR9 is in fact the long-lost object 6344 P-L. 6344 P-L was last seen in 1960, and ever since has had the peculiar distinction of being the only Potentially Hazardous Asteroid without a formal designation. "The object was long recognized to be dangerous, but we didn't know where it was," says Jenniskens. "Now it is no longer just out there." A designation as Potentially Hazardous means that 2007 RR9 is one of 886 (not 887) known asteroids bigger than 150 m (500 ft) in diameter that come to within 0.05 astronomical units of Earth's orbit (roughly 7,480,000 km or 4,650,000 miles). The size is estimated on the basis of the object's observed brightness and an assumed reflectance of 13 percent. Jenniskens believes that this object may not, in fact, be an asteroid. "This is a now-dormant comet nucleus, a fragment of a bigger object that, after breaking up in the not-so-distant past, may have caused the gamma Piscid shower of slow meteors (IAU #236) that is active in mid-October and early November," he says. 2007 RR9 moves in a 4.70-year orbit, nearly all the way out to the distance of Jupiter. Because of this elongated orbit, it has a Tisserand parameter of T = 2.94, which defines it dynamically as a Jupiter Family Comet (T = 2.0 - 3.0), not an asteroid (T > 3.0). So far, this object has not yet been seen to be even weakly active, but the now dormant comet is still moving closer to the Sun. It is sliding rapidly toward visibility in the southern hemisphere, and is expected to brighten to magnitude +18.5 in mid-October. According to Gareth V. Williams of the Minor Planet Center, it will pass Earth around November 6 at 0.07 AU, when the minor planet is at high latitudes in southern skies. The original designation of P-L stands for "Palomar-Leiden," the juxtaposition of two observatory names that reflect what was a very fruitful collaboration by the trio of pioneer asteroid searchers Tom Gehrels of the University of Arizona, and Ingrid van Houten-Groeneveld and her husband Cornelis Johannes van Houten. Gehrels made a sky survey using the 48-inch Schmidt Telescope at the famed Palomar Observatory, long before modern asteroid reconnaisances, and shipped the photographic plates to the van Houtens at Leiden Observatory in the Netherlands. There, Ingrid discovered 6344 P-L on four plates taken on September 24-28, 1960. The trio are jointly credited with several thousand asteroid discoveries, but only 6344 P-L is a potential danger to Earth. Peter Jenniskens is a meteor astronomer with the SETI Institute and author of "Meteor Showers and their Parent Comets" published by Cambridge University Press (2006). He is also credited with the identification of the parent body of the Quadrantid meteor shower. As it happens, he graduated from Leiden Observatory in 1992, before joining the SETI Institute. Adapted from materials provided by SETI Institute.

Vote now for Hubble's 10 most spectacular photo's

So far the Hourglass Nebula is ranked #5. Cast your vote and view the results. Many of these are absolutely amazing. http://www.space.com/bestimg/index.php?cat=hst

K/T impactor source identified

September 5, 2007 Scientists believe they have found the parent object that produced the asteroid that wiped out the dinosaurs 65 million years ago. Provided by SwRI The impactor believed to have wiped out the dinosaurs and other life forms on Earth some 65 million years ago has been traced back to a breakup event in the main asteroid belt. A joint U.S.-Czech team from Southwest Research Institute (SwRI) and Charles University in Prague suggests that the parent object of asteroid (298) Baptistina disrupted when it was hit by another large asteroid, creating numerous large fragments that would later create the Chicxulub crater on the Yucatan Peninsula as well as the prominent Tycho crater found on the Moon. The team of researchers, including Dr. William Bottke (SwRI), Dr. David Vokrouhlicky (Charles University, Prague) and Dr. David Nesvorny (SwRI), combined observations with several different numerical simulations to investigate the Baptistina disruption event and its aftermath. A particular focus of their work was how Baptistina fragments affected the Earth and Moon. At approximately 170 kilometers in diameter and having characteristics similar to carbonaceous chondrite meteorites, the Baptistina parent body resided in the innermost region of the asteroid belt when it was hit by another asteroid estimated to be 60 kilometers in diameter. This catastrophic impact produced what is now known as the Baptistina asteroid family, a cluster of asteroid fragments with similar orbits. According to the team's modeling work, this family originally included approximately 300 bodies larger than 10 kilometers and 140,000 bodies larger than 1 kilometer. Once created, the newly formed fragments' orbits began to slowly evolve due to thermal forces produced when they absorbed sunlight and re-radiated the energy away as heat. According to Bottke, "By carefully modeling these effects and the distance traveled by different-sized fragments from the location of the original collision, we determined that the Baptistina breakup took place 160 million years ago, give or take 20 million years." The gradual spreading of the family caused many fragments to drift into a nearby "dynamical superhighway" where they could escape the main asteroid belt and be delivered to orbits that cross Earth's path. The team's computations suggest that about 20 percent of the surviving multi-kilometer- sized fragments in the Baptistina family were lost in this fashion, with about 2 percent of those objects going on to strike the Earth, a pronounced increase in the number of large asteroids striking Earth. Support for these conclusions comes from the impact history of the Earth and Moon, both of which show evidence of a two-fold increase in the formation rate of large craters over the last 100 to 150 million years. As described by Nesvorny, "The Baptistina bombardment produced a prolonged surge in the impact flux that peaked roughly 100 million years ago. This matches up pretty well with what is known about the impact record." Bottke adds, "We are in the tail end of this shower now. Our simulations suggest that about 20 percent of the present-day, near-Earth asteroid population can be traced back to the Baptistina family." The team then investigated the origins of the 180 kilometer diameter Chicxulub crater, which has been strongly linked to the extinction of the dinosaurs 65 million years ago. Studies of sediment samples and a meteorite from this time period indicate that the Chicxulub impactor had a carbonaceous chondrite composition much like the well-known primitive meteorite Murchison. This composition is enough to rule out many potential impactors but not those from the Baptistina family. Using this information in their simulations, the team found a 90 percent probability that the object that formed the Chicxulub crater was a refugee from the Baptistina family. These simulations also showed there was a 70 percent probability that the lunar crater Tycho, an 85 kilometer crater that formed 108 million years ago, was also produced by a large Baptistina fragment. Tycho is notable for its large size, young age and its prominent rays that extend as far as 1,500 kilometers across the Moon. Vokrouhlicky says, "The probability is smaller than in the case of the Chicxulub crater because nothing is yet known about the nature of the Tycho impactor." This study demonstrates that the collisional and dynamical evolution the main asteroid belt may have significant implications for understanding the geological and biological history of Earth. As Bottke says, "It is likely that more breakup events in the asteroid belt are connected in some fashion to events on the Earth, Moon and other planets. The hunt is on!" The article, "An asteroid breakup 160 Myr ago as the probable source of the K/T impactor," was published in the September 6 issue of Nature.

What is Dark Energy?

With all the talk lately about Dark Energy, I wanted to fully understand what it was. Going to Wikipedia, it states: In physical cosmology, dark energy is a hypothetical form of energy that permeates all of space and tends to increase the rate of expansion of the universe. [1] Assuming the existence of dark energy is the most popular way to explain recent observations that the universe appears to be expanding at an accelerating rate. In the standard model of cosmology, dark energy currently accounts for almost three-quarters of the total mass-energy of the universe. Two proposed forms for dark energy are the cosmological constant, a constant energy density filling space homogeneously,[2] and scalar fields such as quintessence or moduli, dynamic fields whose energy density can vary in time and space. In fact contributions from scalar fields which are constant in space are usually also included in the cosmological constant. The cosmological constant is thought to arise from the vacuum energy. Scalar fields which do change in space are hard to distinguish from a cosmological constant, because the change may be extremely slow. High-precision measurements of the expansion of the universe are required to understand how the speed of the expansion changes over time. The rate of expansion is parameterized by the cosmological equation of state. Measuring the equation of state of dark energy is one of the biggest efforts in observational cosmology today. Adding the cosmological constant to cosmology's standard FLRW metric leads to the Lambda-CDM model, which has been referred to as the "standard model" of cosmology because of its precise agreement with observations. As we hear more, I will try to update my postings.

Talk to me

I want to hear what you have to say. What would you like to see on this site.

Have you bought a plot on the moon yet?

You might want to hold off on that. According to Discover magazine, Dennis Hope, who runs Lunar Embassy will sell you a plot on the moon for $19.99 plus tax because of a loop-hole in the 1967 United Nations Outer Space Treaty. This treaty prohibits nations from owning the moon, however he claims that it does not prohibit individuals. Ram Jakuh, a law professor at the Institute of Air and Space Law at McGill University in Toronto states that the moon is common property of the international community so individuals, like nations cannot own it. He states, "No one owns the moon. No one can own any property in outer space." The U.N.'s treaty states that the state (or nation) has jurisdiction over any individuals rights. In other words, if you claim you own the land where a nation wants to place a space station, you forfeit you claim. Dennis Hope has made $9 million selling plots on the moon and plans to sell more. Although it is up to you if you want to give him your hard earned $20, I would rather spend it on myself like going to a movie or dinner. Their web site is http://www.lunarembassy.com/. Through this site you can also purchase property on Mars, Venus, Io, and Mercury. You can purchase domain names on the Extra Terrestrial Internet as well. Can we say hoax? What gets me is the people who have actually purchased plots. The article names, Barbara Walters, George Lucas, Ronald Regan and first President Bush. Although some people might just think that it's "cool" to own a piece of the moon, I can't believe that 4.25+ million people has made one man a multi-millionaire. Although I don't think that the law would ever make him return any of the monies, let's hope someone can shut him down quickly. Now it's your turn to decide. Mr. Hope claims that he is not exploiting anything, however he does state that the treaty does not allow for the "exploitation of the Moon and other celestial bodies for profit purposes." I have one question, isn't this the same thing? Check out this web site before you decide. http://www.lunarregistry.com/info/embassy.shtml

Great shot of the Aurigids by Alan Dyer

Oh, my! How fantastic! These may very well be the first pictures posted of this event that is not scheduled to occur again in our lifetime. Note the tail. Right before dawn.

2000-Year-Old Meteors to Rain Down on August 31, 2007

Peter Jenniskens, Ph.D.Meteor Astronomer, Carl Sagan Center, SETI InstituteSPACE.comThu Aug 23, 10:30 AM ET The meteors that are about to rain down in the early morning of September 1 date from around 4 A.D., the latest calculations show. It is not often that we can tell when a shooting star was first released from a comet into space, to travel as a meteoroid in an orbit around the Sun, and finally collide with Earth's atmosphere to shine as a meteor for our enjoyment. Most meteors that sporadically flash across the sky on a dark moonless night date from anonymous times. Only in recent years have we learned to trace young meteor showers, just a few revolutions old, to their date of origin. The oldest such shower, but only one revolution old, is due in the early morning of September 1, 2007. Our calculations indicate Earth is about to cross the dust trail of comet Kiess, a comet that takes some 2000 years to complete one orbit around the Sun. The trail is very narrow, so Earth will be hosed by meteoroids for only about an hour and a half. The meteoroids will approach from the direction of the constellation Auriga, the charioteer, in the north-eastern part of the sky, causing a meteor shower called the "Aurigids." If you spot one of those meteors, you may be only the fourth person alive who is known to have seen this meteor shower. In recent times, the shower was spotted in 1994 by two observers and in 1986 by one observer. If you are lucky enough to catch a picture of an Aurigid meteor using your digital camera, you will be the very first to do so. Tips on how to observe meteors and where to report the results can be found at: http://aurigid.seti.org/ The shower is visible from only part of the world. If you live in the western parts of the USA, Canada and Mexico, including Hawaii and Alaska, you might spot an Aurigid meteor. Plan to step out around 4 A.M. PDT in the early morning, warmly dressed with a blanket wrapped around your shoulders, away from city smog, with the Moon behind an obstruction, and with a wide view on the sky. Gaze up at the sky, waiting, and you may spot one of these elusive bits of matter that Comet Kiess lost 2000 years ago. This is your only chance to see this shower; the dust trail is not going to hit again in our lifetime. It is also our best chance yet to test meteor shower prediction models and look for evidence of the crust that a comet is suspected to build up during the time it spends in the Oort cloud. Comets in shorter orbits have long lost this pristine crust. Jon Giorgini of JPL/Caltech has identified observations of Comet Kiess when it returned in 1911. The orbit is now better determined than before and calculating backwards in time puts the comet near Earth's orbit in 4 A.D., give or take 40 years. It was at that time that the dust was released that we now see as meteors. The dust was ejected in wider orbits than the comet and took somewhat longer to return. Jeremie Vaubaillon of Caltech calculated where the dust would end up at Earth's orbit on September 1, 2007, if it was ejected in 4 A.D. and he found that, indeed, the dust trail will be in Earth's path. The peak is expected at 11:33 UT, or 4:33 a.m. PDT, give or take 20 minutes. From past Aurigid showers, we anticipate a shower of mostly -2 to +3 magnitude meteors with a peak Zenith Hourly Rate about 200 per hour during a 10-minute interval, with rates above 100 per hour for only 25 minutes. With a bright Moon in the sky, only 4 days past full, that translates to several tens of chances to make a wish on a meteor from around 4 A.D. To increase our chances of catching these rare meteors, we will be observing the shower from two Gulfstream GV aircraft (flying at 45,000 ft) on a parallel flight path from Wisconsin, over the Bay Area in California, and on to the Pacific in the early morning of September 1. An international team of 24 researchers will have 21 windows to aim their cameras through. The cameras are of different types, some similar to your own digital camera and camcorder, others using technologies more familiar to cameras used on astronomical telescopes or those in night vision goggles. Near the horizon, we hope to see many more meteors than will be visible from the ground, but each of us will be glad if the shower actually shows. You can participate in this research by making an effort to photograph or film the Aurigid meteors. Chances are that one of you, not us, will catch the brightest Aurigid out there. Even simple cameras can provide information about how the meteoroids break apart, as each image is composed of three different images: one in blue light, another in green, and one in red. Each color traces different aspects of the meteor's light. More information at our Aurigid Multi-Instrument Aircraft Campaign mission website: http://aurigid.seti.orgAll About Meteors Gallery: 2006 Perseid Meteor Shower Gallery: Best of the Leonid Meteor Shower Original Story: 2000-Year-Old Meteors to Rain Down on August 31, 2007

Astronomers find a hole in the universe

By SETH BORENSTEIN, AP Science WriterFri Aug 24, 7:45 AM ET Astronomers have stumbled upon a tremendous hole in the universe. That's got them scratching their heads about what's just not there. The cosmic blank spot has no stray stars, no galaxies, no sucking black holes, not even mysterious dark matter. It is 1 billion light years across of nothing. That's an expanse of nearly 6 billion trillion miles of emptiness, a University of Minnesota team announced Thursday. Astronomers have known for many years that there are patches in the universe where nobody's home. In fact, one such place is practically a neighbor, a mere 2 million light years away. But what the Minnesota team discovered, using two different types of astronomical observations, is a void that's far bigger than scientists ever imagined. "This is 1,000 times the volume of what we sort of expected to see in terms of a typical void," said Minnesota astronomy professor Lawrence Rudnick, author of the paper that will be published in Astrophysical Journal. "It's not clear that we have the right word yet ... This is too much of a surprise." Rudnick was examining a sky survey from the National Radio Astronomy Observatory, which essentially takes radio pictures of a broad expanse of the universe. But one area of the universe had radio pictures indicating there was up to 45 percent less matter in that region, Rudnick said. The rest of the matter in the radio pictures can be explained as stars and other cosmic structures between here and the void, which is about 5 to 10 billion light years away. Rudnick then checked observations of cosmic microwave background radiation and found a cold spot. The only explanation, Rudnick said, is it's empty of matter. It could also be a statistical freak of nature, but that's probably less likely than a giant void, said James Condon, an astronomer at the National Radio Astronomy Observatory. He wasn't part of Rudnick's team but is following up on the research. "It looks like something to be taken seriously," said Brent Tully, a University of Hawaii astronomer who wasn't part of this research but studies the void closer to Earth. Tully said astronomers may eventually find a few cosmic structures in the void, but it would still be nearly empty. Holes in the universe probably occur when the gravity from areas with bigger mass pull matter from less dense areas, Tully said. After 13 billion years "they are losing out in the battle to where there are larger concentrations of matter," he said. Retired NASA astronomer Steve Maran said of the discovery: "This is incredibly important for something where there is nothing to it."

Lunar Eclipse Photos

All right, I promised you photos. It's hard to find them right now, I'm sure there are still many that getting posted. However, I have three spectacular photos of the moon going to total and the blood-red moon photo of the total eclipse. Ohhhhhh! This was the photo I took below, but with a 35mm... I never thought I would get one like this and of course I didn't. Maybe I'll keep this one and pretend I took it. *smiles* Blood-red! Wow! Now I know everyone thinks my shot below is better than any of these, but don't judge to harshly. These people did pretty well in my opinion.

Wow! What a show!

I got myself up and headed outside this morning to see a spectacular show. I was quickly disappointed as the moon had slipped behind the trees. Thinking quickly I got in my car and drove to my parents house a few blocks away, up the hill from me. I pulled into their driveway and saw the best site...sitting on their front porch I could see everything. The sky was clear, no trees and the best start to the total lunar eclipse. Unfortunately, I was unable to watch it finish. The moon would have set anyway before it had finished. I hope you had a great view and would love to see some pictures. This was my lame attempt for a picture. You can see the very bottom of the moon (yes that is what this picture is of...) Coming back to my computer, looking at this picture from the distance you can make out the sides of the moon too...I'm better then I thought. *smiles* I will post some pictures here of the eclipse after I find some good ones.

Tonight is the night for the total eclipse

Hope you have clear skys for the eclipse tonight. Unfortuantly I am on the east coast, but it should still be pretty spectacular. Let me know how your night went.

Tips on Meteor Watching

How can I best view a meteor shower? If you live near a brightly lit city, drive away from the glow of city lights and toward the constellation from which the meteors will appear to radiate. For example, drive north to view the Leonids. Driving south may lead you to darker skies, but the glow will dominate the northern horizon, where Leo rises. Perseid meteors will appear to "rain" into the atmosphere from the constellation Perseus, which rises in the northeast around 11 p.m. in mid-August. After you've escaped the city glow, find a dark, secluded spot where oncoming car headlights will not periodically ruin your sensitive night vision. Look for state or city parks or other safe, dark sites. Once you have settled at your observing spot, lay back or position yourself so the horizon appears at the edge of your peripheral vision, with the stars and sky filling your field of view. Meteors will instantly grab your attention as they streak by. How do I know the sky is dark enough to see meteors? If you can see each star of the Little Dipper, your eyes have "dark adapted," and your chosen site is probably dark enough. Under these conditions, you will see plenty of meteors. What should I pack for meteor watching? Treat meteor watching like you would the 4th of July fireworks. Pack comfortable chairs, bug spray, food and drinks, blankets, plus a red-filtered flashlight for reading maps and charts without ruining your night vision. Binoculars are not necessary. Your eyes will do just fine.

Warp speed ahead Mr. Scott...

I find myself staring at this picture in awe of the beauty and magnifigance of the cosmos around us. Wondering how many of these solar systems may hold life and feeling disappointed that I will never know. I also wonder, if there is life out there, are they staring at us like we are at them. Makes me wonder...

Mira, streaking through space at extraordinary speeds, leaves a wake 13 light-years long.

August 15, 2007 Material blowing off Mira is forming a wake 13 light-years long, or thousands of times the length of our solar system. The space-based Galaxy Evolution Explorer (GALEX) was scanning the star during its ongoing sky survey in ultraviolet light when astronomers noticed what looked like a comet with a gargantuan tail. Mira, Latin for "wonderful," has been a favorite of astronomers for about 400 years. It is a fast-moving red giant, which sheds massive amounts of surface material, but nothing like this has ever been seen before around a star. "This is an utterly new phenomenon to us, and we are still in the process of understanding the physics involved," said Mark Seibert of Carnegie Observatories in Pasadena, California. "We hope to be able to read Mira's tail like a ticker tape to learn about the star's life." Astronomers say Mira's tail offers a unique opportunity to study how stars like our sun die and ultimately seed new solar systems. As Mira hurls along, its tail drops off carbon, oxygen and other important elements needed for new stars, planets, and possibly even life to form. This tail material, visible now for the first time, has been shed over the past 30,000 years. Billions of years ago, Mira was like our Sun. Over time, it began to swell into a variable red giant — a pulsating, puffed-up star that periodically grows bright enough to see with the naked eye. Mira will eventually eject all of its remaining gas into space, forming a colorful shell, or a planetary nebula. The nebula will fade with time, leaving only the burnt-out core of the original star (a white dwarf). Compared to other red giants, Mira is traveling unusually fast, possibly due to gravitational boosts from other passing stars. It now plows along at 291,000 mph (130 kilometers per second). Racing along with Mira is a small, distant companion thought to be a white dwarf. The pair, also known as Mira A (the red giant) and Mira B, orbit slowly around each other as they travel together in the constellation Cetus, 350 light-years from Earth. In addition to Mira's tail, GALEX also discovered a bow shock, a buildup of hot gas, in front of the star, and two sinuous streams of material coming out of the star's front and back. Astronomers think hot gas in the bow shock is heating up the gas blowing off the star, causing it to fluoresce with ultraviolet light. This glowing material then swirls around behind the star, creating a turbulent, tail-like wake. The process is similar to a speeding boat leaving a choppy wake, or a steam train producing a trail of smoke. "GALEX is so exquisitely sensitive to ultraviolet light and it has such a wide field of view that it is uniquely poised to scan the sky for previously-undiscovered ultraviolet activity," said Barry F. Madore, senior research astronomer at the Carnegie Observatories. The fact that Mira's tail only glows with ultraviolet light might explain why other telescopes have missed it. "We never would have predicted a turbulent wake behind a star that glows only with ultraviolet light," said Seibert. "Survey missions like the Galaxy Evolution Explorer can provide many surprises."

Nasa reports Total Lunar Eclipse

A total eclipse of the Moon occurs during the early morning of Tuesday, August 28, 2007. The event is widely visible from the United States and Canada as well as South America, the Pacific Ocean, western Asia and Australia. During a total lunar eclipse, the Moon's disk can take on a dramatically colorful appearance from bright orange to blood red to dark brown and (rarely) very dark gray. An eclipse of the Moon can only take place at Full Moon, and only if the Moon passes through some portion of Earth's shadow. The shadow is actually composed of two cone-shaped parts, one nested inside the other. The outer shadow or penumbra is a zone where Earth blocks some (but not all) of the Sun's rays. In contrast, the inner shadow or umbra is a region where Earth blocks all direct sunlight from reaching the Moon. If only part of the Moon passes through the umbra, a partial eclipse is seen. However, if the entire Moon passes through the umbral shadow, then a total eclipse of the Moon occurs. For more information on how, what, why, where and when of lunar eclipses, see the special web page lunar eclipses for beginners.

Definitions and explanations of Astronomy Terms

Twilight - This is the time before sunrise and after sunset where it is still light outside, but the sun is not in the sky. Civil Twilight - This is defined to be the time period when the sun is no more than 6 degrees below the horizon at either sunrise or sunset. The horizon should be clearly defined and the brightest stars should be visible under good atmospheric conditions (i.e. no moonlight, or other lights). One still should be able to carry on ordinary outdoor activities. Nautical Twilight - This is defined to be the time period when the sun is between 6 and 12 degrees below the horizon at either sunrise or sunset. The horizon is not defined and the outline of objects might be visible without artificial light. Ordinary outdoor activities are not possible at this time without extra illumination. Astronomical Twilight - This is defined to be the time period when the sun is between 12 and 18 degrees below the horizon at either sunrise or sunset. The sun does not contribute to the illumination of the sky before this time in the morning, or after this time in the evening. In the beginning of morning astronomical twilight and at the end of astronomical twilight in the evening, sky illumination is very faint, and might be undetectable. Length Of Day - This is defined to be the time of Actual Sunset minus the time of Actual Sunrise. The change in length of daylight between today and tomorrow is also listed when available. Length Of Visible Light - This is defined to be the time of Civil Sunset minus the time of Civil Sunrise. Altitude (or Elevation) - First, find your azimuth. Next, the Altitude (or elevation) is the angle between the Earth's surface (horizon) and the sun, or object in the sky. Altitudes range from -90° (straight down below the horizon, or the nadir) to +90° (straight up above the horizon or the Zenith) and 0° straight at the horizon. Azimuth - The azimuth (az) angle is the compass bearing, relative to true (geographic) north, of a point on the horizon directly beneath the sun. The horizon is defined as an imaginary circle centered on the observer. This is the 2-D, or Earth's surface, part of calculating the sun's position. As seen from above the observer, these compass bearings are measured clockwise in degrees from north. Azimuth angles can range from 0 - 359°. 0° is due geographic north, 90° due east, 180° due south, and 360 due north again. Hour Angle of the Sun - The Solar Hour Angle of the Sun for any local location on the Earth is zero° when the sun is straight overhead, at the zenith, and negative before local solar noon and positive after solar noon. In one 24-hour period, the Solar Hour Angle changes by 360 degrees (i.e. one revolution). Mean Anomaly of the Sun - The movement of the Earth around the Sun is an ellipse. However, if the movement of the Earth around the Sun were a circle, it would be easy to calculate its position. Since, the Earth moves around the sun about one degree per day, (in fact, it's 1/365.25 of the circle), we say the Mean Anomaly of the Sun is the position of the Earth along this circular path. The True Anomaly of the Sun is the position along its real elliptical path. Obliquity - Obliquity is the angle between a planet's equatorial plane and its orbital plane. Right Ascension of the Sun - The Celestial Sphere is a sphere where we project objects in the sky. We project stars, the moon, and sun, on to this imaginary sphere. The Right Ascension of the Sun is the position of the sun on our Celestial Sphere. Solar Noon (and Solar Time) - Solar Time is based on the motion of the sun around the Earth. The apparent sun's motion, and position in the sky, can vary due to a few things such as: the elliptical orbits of the Earth and Sun, the inclination of the axis of the Earth's rotation, the perturbations of the moon and other planets, and of course, your latitude and longitude of observation. Solar Noon is when the sun is at the highest in the sky, and is defined when the Hour Angle is 0°. Solar Noon is also the midpoint between Sunrise and Sunset. Sun Declination - The Declination of the sun is how many degrees North (positive) or South (negative) of the equator that the sun is when viewed from the center of the earth. The range of the declination of the sun ranges from approximately +23.5° (North) in June to -23.5° (South) in December.