Strong Leonid Meteor Shower Expected Nov. 17 - Big Big Forums

Jolie Rouge · 11-04-2009, 05:52 PM

Strong Leonid Meteor Shower Expected Nov. 17
[Joe Rao Skywatching Columnist
space.com
Mon Nov 2, 2:01 pm ET

Circle Nov. 17 on your calendar, for early that morning a moderate to possibly very strong showing of annual Leonid meteor shower is likely.

The very strong display will favor those living across most of central and eastern Asia. In this region, meteor rates might briefly rise to a few hundred per hour (the time frame for the most intense activity is anticipated sometime around 21:40 GMT).

A far more modest, but still potentially enjoyable display of a few dozen Leonid meteors per hour is expected to favor North America. In the United States and Canada, eastern observers will be particularly well-positioned for maximum activity, expected sometime between 3:30 and 5:30 a.m. EST, when the radiant of the Leonid shower will be well up in the dark southeastern sky.

A meteor shower's radiant is the perspective point from which all the meteors would appear to originate if their paths were traced backward far enough. The higher the radiant is, the more meteors flash into view all over the sky (though meteors can appear anywhere in the sky, so focusing on the radiant is not necessary).

The Leonid radiant is within the so-called "Sickle" of Leo; a backwards question-mark pattern of stars that outlines the head and mane of the constellation Leo, the Lion. Hence the meteors are known as "Leonids."

Not in the East? Don't fret. Observers all across North America may experience a good Leonid show with "shooting stars" streaking across the sky every few minutes.

Also a big plus in 2009 is the lack of any interference from the moon. New moon is on Nov. 16, so skies will be dark for catching the fainter meteor streaks. And the first light of dawn will not break until shortly after 5 a.m. local time.

Europe and Africa appear largely out of luck. This year's first round of expected enhanced activity will happen chiefly during their daylight hours. The second, stronger outburst will occur during early evening, but that's hours before Leo comes above the horizon. Europeans might try watching before sunrise on the morning of Nov. 17, but are not likely to see more than 10 or 15 Leonids per hour.

Cosmic garbage

It may not sound sexy, but simply put, the reason for this year's anticipated good Leonid showing is due to cosmic garbage.

The Leonids are known to be made up of cosmic litter from a small – 2.2 mi (3.6 km) – dusty comet discovered by two astronomers in the late 19th century and christened Tempel-Tuttle. The Leonid meteors are thought to be the dusty legacy of Comet Tempel-Tuttle because the dust is moving around the sun in virtually the same orbit as the comet.

As the Earth encounters the debris left behind by the comet's previous passes through our orbit, these tiny fragments of the comet – typically no bigger than a sand grain or the occasional pea – impact our atmosphere at speeds of up to 45 miles per second (71 kps), causing them to blaze briefly but brightly in the night sky.

The Leonids are not a one-night stand. The dust from Tempel-Tuttle spangles the sky for a few nights every year in mid-November. This year, the peak is expected during the predawn hours of Nov. 17, but early-morning hours on the dates surrounding Nov. 17 could provide a decent show, too.

Tempel-Tuttle last passed near the sun and Earth more than a decade ago (in 1998) and for several years thereafter the Leonids put on some spectacular displays, producing many hundreds – even thousands of meteors per hour. But with the departed comet now cruising through the outer part of the solar system, we typically would not expect to see more than 8 or 10 Leonids during an hour's watch.

Yet if several meteor scientists are correct, this year will be atypical. The researchers have produced various models of the Leonid stream and all of them are indicating that the Earth will intersect a few "rivers of rubble" left behind by Comet Tempel-Tuttle.

Asian forecast

In particular, French astronomer, Jeremie Vaubaillon, Russian astronomer, Mikhail Maslov and Americans Bill Cooke and Danielle Moser of NASA's Meteoroid Environment Office are all in agreement that material that was ejected from the comet's nucleus during the years 1466 and 1533 will likely produce a very strong meteor display over much of Asia. "The year 2009 will not see a Leonid storm, but an outburst for sure," Vaubaillon said, adding that "there are still some uncertainties."

Last year, the material that was shed by the comet back in 1466 produced about 100 Leonids per hour. This year, Earth will cross through the 1466 stream again, but this time much closer – 42,000 mi. (68,000 km) – to the center on Nov. 17 at around 21:40 GMT. This time favors central and eastern Asia (and it comes during daylight in North America). In addition, at about this same time, the Earth will also be passing through dust ejected by the comet in 1533. The consensus forecast among the astronomers for this year suggests anywhere from 130 to perhaps 300 Leonids per hour in Asia, but this spread has been calibrated chiefly using last year's Earth interaction solely with the 1466 stream. "But nothing is known (about) the 1533 stream," Vaubaillon said.

North America forecast

About 12 to 14 hours before the main event, Earth is forecast to sideswipe a stream of dust that was loosed from the nucleus of Comet Tempel-Tuttle in the year 1567, passing to within 188,000 mi. (302,000 km.) of the stream's center. This interaction could provide smodest activity for North Americans.

The best guesstimate is for perhaps 25 to 30 Leonids per hour, which would most likely target a time frame sometime between roughly 3:30 and 5:30 a.m. ET (12:30 to 2:30 a.m. PT).

For North American observers, the emphasis might be on quality, not quantity; for while the numbers might not be exceptionally high as compared to Asia, a few of these meteors, though visible for a just a fraction of a second, might leave bright trails of ionized atoms in their wake that hang in the sky for many seconds – or possibly even minutes – as these tiny dust particles streak through our atmosphere at altitudes of 80 to 100 miles (130 to 160 km).

And seeing even just one such outstandingly bright meteor like that can make a cold early morning vigil worthwhile.

Advance practice

If you want to get started early, you can practice for the big event.

The first Leonid forerunners might be sighted as early as Nov. 10, although overall activity will be rather low and spotty – perhaps only a few per hour at most. Around Nov. 16, in the predawn, Leonid activity will noticeably increase to perhaps four to eight per hour.

Observers on the lookout for early Leonids might also notice a number of rather slow moving meteors appearing to emanate from around the constellation of Taurus, the Bull (high in the southwest sky after midnight). These are the Taurid meteors and are most active between Nov. 5 and 12 when they can produce as many as five or 10 per hour.

Editor's Note: SPACE.com will provide a Leonids 2009 Viewer's Guide on Friday, Nov. 13.

Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for The New York Times and other publications, and he is also an on-camera meteorologist for News 12 Westchester, New York.

http://news.yahoo.com/s/space/200911...rexpectednov17

Jolie Rouge · 11-16-2009, 05:58 PM

Strong Leonid Meteor Shower Peaks Early Tuesday Morning
Robert Roy Britt - Editorial Director SPACE.com
Mon Nov 16, 12:30 pm ET

One of the best annual meteor showers will peak in the pre-dawn hours Tuesday, and for some skywatchers the show could be quite impressive.

The best seats are in Asia, but North American observers should be treated to an above average performance of the Leonid meteor shower, weather permitting. The trick for all observers is to head outside in the wee hours of the morning – between 1 a.m. and dawn – regardless where you live.

The Leonids put on a solid show every year, if skies are clear and moonlight does not interfere. This year the moon is near its new phase, and not a factor. For anyone in the Northern Hemisphere with dark skies, away from urban and suburban lighting, the show should be worth getting up early to see.

"We're predicting 20 to 30 meteors per hour over the Americas, and as many as 200 to 300 per hour over Asia," said Bill Cooke of NASA's Meteoroid Environment Office. Other astronomers who work in the nascent field of meteor shower prediction have put out similar forecasts.

Urban dwellers and suburbanites will see far fewer, as the fainter meteors will be drowned out by local lights.

Behind the Leonids

The Leonids are created by the comet Tempel-Tuttle, which passes through the inner solar system every 33 years on its orbit around the sun. Each time by, it leaves a new river of debris, mostly bits of ice and rock no bigger than a sand grain but a few the size of a pea or marble.

Over time, these cosmic streams spread out, so predicting exactly what will happen is difficult.

"We can predict when Earth will cross a debris stream with pretty good accuracy," Cooke said. "The intensity of the display is less certain, though, because we don't know how much debris is in each stream."

When Earth plows into the debris, the bits hit the atmosphere and vaporize, creating sometimes dramatic streaks of light and the occasional fireball with a smoky-looking trail that can remain visible for several minutes.

The Leonid stream is moving in the opposite direction of Earth, producing impact speeds of 160,000 mph (72 kilometers per second) – higher than many other meteors.

"Such speeds tend to produce meteors with hues of white, blue, aquamarine and even green," says Joe Rao, SPACE.com's skywatching columnist.

How to watch

The best viewing will be in rural areas. Get out of town if you can. If you have local lights, scout a location in advance where the lights are blocked by a building, tree or hill.

Dress warmly, and take a blanket or lounge chair so you can lie back and scan as much of the sky as possible. "At this time of year, meteor watching can be a long, cold business," Rao reminds people.

Leonids can appear anywhere, but if you trace them back, they all point to a hub, or radiant, in the constellation Leo – hence the name.

Give your eyes 15 minutes to adjust to the darkness. Then give the show at least a half-hour. The hourly rates stated above typically come in bursts, with lulls that may test your patience. No special equipment is needed. Telescopes and binoculars are of no use because meteors move too quickly.

When to watch

Earth will pass through one of the denser debris streams at around 4 a.m. EST (1 a.m. PST) Tuesday. If you have only an hour or less to watch, center it around this time. Leo will be high in the sky for East Coast skywatchers, putting more meteors into view. In the West, Leo will be low in the eastern sky at this time, so fewer shooting stars will be above the horizon, and therefore Western skywatchers should also try to stick it out until daybreak.

Across Europe, the best bet is to watch anytime between 1 a.m. and daybreak local time.

The planet will pass through an even denser stream later, just before dawn Wednesday in Indonesia and China, but that show won't be visible from North America because it will be daytime here.

http://news.yahoo.com/s/space/200911...tuesdaymorning