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

2000-Year-Old Meteors to Rain Down on August 31, 2007
Peter Jenniskens, Ph.D. -- Meteor Astronomer, Carl Sagan Center, SETI Institute -- SPACE.com
Thu 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.

http://news.yahoo.com/s/space/200708...s5YGiIObGs0NUE

More information at our Aurigid Multi-Instrument Aircraft Campaign mission website: http://aurigid.seti.org

Viewer's Guide: Tuesday Morning's Lunar Eclipse
Joe Rao -- SPACE.com Skywatching Columnist
Fri Aug 24, 5:30 PM ET

Tuesday morning, Aug. 28 brings us the second total lunar eclipse of 2007. Those living in the Western Hemisphere and eastern Asia will be able to partake in at least some of this sky show.

The very best viewing region for viewing this eclipse will fall across the Pacific Rim, including the West Coast of the United States and Canada, as well as Alaska, Hawaii, New Zealand and eastern Australia. All these places will be able to see the complete eclipse from start to finish.


Europeans will miss out on the entire show, as the Moon will be below the horizon during their mid and late morning hours.


What to look for


The eclipse will begin when the Moon enters the faint outer portion, or penumbra, of the Earth's shadow about an hour before it begins moving into the umbra. The penumbra, however, is all but invisible to the eye until the Moon becomes deeply immersed in it. Look for a slight hint of shading or smudginess on the eastern (left) edge of the lunar disk about 40 minutes after the Moon first enters the penumbral shadow.


The most obvious part of the eclipse will be when the Moon is passing through the dark umbral shadow of the Earth. On this occasion, the full Moon will track just to the south of the center of the Earth's umbra; deep path almost through the center of the umbra which will result in a total phase lasting an unusually long 1 hour 30 minutes (the maximum possible is 1 hour 47 minutes).


Because some of the sunlight striking our planet is diffused and scattered by our atmosphere, the Earth's shadow is not entirely dark. Enough of this light reaches the Moon to give it a faint orange or reddish glow even when it's totally eclipsed.


At greatest eclipse the Moon's southern limb will pass 1,039 mi. (1,672 km.) from the outer edge of the dark shadow. This should produce a relatively dark eclipse, with the Moon glowing a dull coppery color along its lower portion and a deep brown or gray over its upper portion. SPACE.com encourages viewers to estimate the Danjon value - a five-point scale of lunar luminosity ("L") to classify eclipses - at mid-totality.


The Moon enters the umbra at 4:51 a.m. EDT (1:51 a.m. PDT). Totality begins at 5:32 EDT (2:52 PDT) and ends after sunrise on the East coast and at 4:22 a.m. PDT.


Where you can see it


As for the region of visibility for this eclipse, it pretty much is the "flip side" of the last eclipse, in March: Whereas Africa, Europe and western Asia had ringside seats for that late-winter spectacle, this time they are completely out of luck. The timing of the eclipse comes during their late morning and early afternoon hours, with the eclipsed Moon below the horizon.


Conversely, almost the entire Pacific Ocean is turned toward the Moon during this August eclipse. In fact, at mid-totality the Moon will appear directly overhead for a spot over the open waters of the Pacific, roughly 1,800 mi. (2,900 km.) south of Hawaii.


And whereas, for the March lunar eclipse those near and along the Pacific Rim could catch a brief view at dawn, while the Americas view coincided with moonrise, in August we are presented with the converse of these circumstances. For the eclipse will already be underway at moonrise for Japan and much of Australia on the evening of Aug. 28.


The rest of eastern Asia will either have the Moon rise during totality, or will see it as it is exiting the Earth's shadow.


But from North America, the eclipse occurs during the early morning hours of Aug. 28.


The Canadian Maritimes will miss totality, as the Moon will set in partial eclipse before it begins.


Across the eastern third of the United States, moonset arrives in the midst of the total phase. So, less than six months after easterners watched the Moon rise during totality, comes the opportunity to be treated to the sight of the Moon setting during totality! However, thanks to advancing morning twilight, plus horizon haze, for those living in the Northeastern and Middle Atlantic States it is likely that the dim Moon (some 10,000 times fainter than a normal full Moon) will more-or-less vanish from view near or just after the onset of totality.


Over the central states, the Moon will set in partial eclipse, while emerging from the umbra; the farther west, the less of the Moon so covered. An interesting observation for watchers in this zone who have an unobstructed eastern and western horizon is to attempt seeing the partially eclipsed setting Moon and the rising Sun at the same time. The Moon will remain above the horizon for a few minutes after sunup.

From the western states, all umbral stages will be visible before moonset affording the best views of totality (in a dark sky) within the contiguous states and more than making up for being completely shut-out of a view of last March's eclipse. And Alaska and Hawaii will see the eclipse happen in the middle of their night. Mid-totality for Anchorage comes at 1:37 a.m. Alaskan Daylight Time and for Honolulu at 12:37 a.m. Hawaii Standard Time.

Coming attraction:

Should clouds interfere with your attempt to view Tuesday's eclipse, you won't have very long to wait for the next opportunity. That will come just under six months from now, on the night of Feb. 20-21. Another total lunar eclipse (the third in less than a year's time) will be visible throughout much of North and South America as well as Europe, Africa and parts of western Asia.

http://news.yahoo.com/s/space/200708...YL7j7ys8H737YB