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Jaw-dropping Leonids

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Jaw-dropping Leonids

On Nov. 18, 2001, sky watchers somewhere will see a dazzling storm of Leonid meteors.

NASA
Marshall Space Flight Center

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see captionNovember 8, 2001: I'll never forget the night of November 17, 1998. It was cold outside my mountain home at 9000 ft. The skies were crystal clear. And it was very dark.

That is, except for the fireballs.

I was sky watching with a friend, both of us experienced astronomers. Nevertheless, we stared upwards like novices, slack-jawed, as if we had never seen the sky before.

We were witnessing the annual Leonid meteor shower. But these were no ordinary Leonids. They were bright, vivid, shadow-casting fireballs. Every five minutes or so we saw one as bright as Venus, and a fair number would have outshined a Full Moon. Some of the most startling left behind glowing trails of debris that lingered in the sky, twisting and turning as they were sheared by high-altitude winds.

Above: A wide angle view of Leonid fireballs on November 17, 1998. Photo credit: Juraj Toth. [more]

It was unforgettable.

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In years since I've heard sky watchers refer to that event as the "1998 Leonid fireball storm." But it wasn't really a storm at all. Meteor rates that night never exceeded a few hundred shooting stars per hour. "We define a meteor storm to be times when observers can see 1000 or more per hour," says Bill Cooke from the NASA Marshall Space Flight Center. "The Leonids of '98 -- as spectacular as they were -- were not a full-fledged storm."

But the Leonids of 2001 will be.

Cooke and other experts agree that when the Leonids return later this month sky watchers in some parts of the world will see a display even better than the one in 1998. Indeed, says Cooke, "what's coming on Nov. 18th could be the biggest event since 1966 [when North Americans enjoyed a Leonid storm numbering 100,000 shooting stars per hour]."

Observers in North America, Hawaii, Australia and Asian countries along the Pacific Rim will be favored for the best views of the 2001 Leonids. Meteor rates in those places could climb as high as 8000 per hour -- not quite as intense as the 1966 storm, but more than enough to make a sky watcher's jaw drop.

2001 Leonid Forecasts

 THE PLACE

THE TIME

THE FORECAST (ZHR)

 North America

 9:00 - 11:00 UT
Sunday Morning, Nov 18th:
4:00 - 6:00 a.m. in New York
1:00 - 3:00 a.m. in Los Angeles

 800 - 4000 per hour

California, Hawaii, Samoa

11:00 - 15:00 UT
Sunday Morning, Nov 18th:
3:00 - 7:00 a.m. in Los Angeles
1:00 - 5:00 a.m. in Hawaii

 100 - 1000 per hour

Australia, Indonesia, Japan, east Asia

17:00 - 19:30 UT
Monday Morning, Nov 19th:
0100 - 03:30 a.m. in Hong Kong
0200 - 04:30 a.m. in Tokyo

800 - 8000 per hour

Table notes: (1) UT is Universal Time, also known as Greenwich Mean Time or GMT. UT values above refer to Nov. 18th. (2) Because of the international date line, observers in Australian and Asian countries will see their Leonids before dawn on Nov. 19th local time. (3) ZHR is the Zenithal Hourly Rate -- that is, the number of meteors a observer with ideally dark skies would see if the constellation Leo were directly overhead. The range in predicted ZHRs reflects differences among the models of various forecasters. [more information]

Leonid meteor storms happen when Earth passes through clouds of dusty debris shed by comet 55P/Tempel-Tuttle when it comes close to the Sun every 33 years. This year our planet is heading for close encounters with four such clouds. They bubbled off Tempel-Tuttle in 1699, 1766, 1799 and 1866.

see caption"Each encounter with a dust cloud will produce an outburst of Leonids over some part of our planet," explains Cooke. "For example, the best place to view the 1799 meteoroids is Hawaii. That's where I'll be!" The 1766 cloud will produce a flurry of Leonids over North America, while the 1699 and 1866 clouds will rain meteors over Australia and east Asia.

Right: Auburn-colored ellipses denote dust clouds shed by comet Tempel-Tuttle in the indicated years. Earth's path through space is blue. This model was formulated by D. Asher and R. McNaught; models advocated by other Leonid forecasters differ somewhat.

"These clouds are long and narrow like a comet's tail," says Cooke. "The younger ones are only 10 or so Earth-diameters wide." Our chances of hitting something so narrow and filamentary are slim. Indeed, most years in November we miss them altogether. Earth glides between the clouds where there is only a sprinkling of meteoroids. At such times Leonid rates remain low: only 10 or 15 meteors per hour.

"In 1998 we passed through material shed by the comet in 1333," says Cooke. "That filament was old and somewhat spread out," so rates never climbed to storm levels. It was nevertheless spectacular because "the smallest bits of dust inside that cloud had been blown away long ago by solar radiation pressure. Only the largest meteoroids remained -- hence the fireballs."

"In 2001 we're running into relatively young clouds, richer in small meteoroids," added Cooke. "Observers from '98 who remember mostly fireballs will be dazzled this year instead by a greater number of ordinary meteors."

see caption

Above: Still frames from a digital movie showing Earth as it glides through a filamentary dust cloud. The encounter triggers a meteor shower from the constellation Leo. Click to view the full 565 kb Quicktime animation created by Digital Radiance, Inc.

Although certain parts of the world are favored for intense activity this year, Cooke encourages people everywhere to watch the sky on Nov. 18th. "The Leonids might surprise us," he says. Predicted outbursts might fizzle, and activity could surge at unexpected times.

Veteran meteor watchers are wary of Leonid predictions because the science of forecasting Leonid meteor storms is still young. The basic techniques were pioneered only three years ago by astronomers David Asher (Armagh Observatory) and Rob McNaught (Australian National University). They correctly predicted a brief meteor storm over the Middle East and Europe in 1999. Then, in 2000, they and others used similar methods to forecast the times of three more Leonid flurries. It's a promising track record, but by no means well-established.

Below: The Leonid radiant, denoted by a red dot, will appear high in the southern sky at 5 o'clock in the morning (local time) as viewed from mid-Northern latitudes. Click to view a southern hemisphere sky map.

see caption

If you're determined to spot some Leonids this year, here is the best strategy: Dress warmly and travel (if necessary) to a dark-sky site away from urban light pollution. Be prepared to watch the sky between midnight and sunrise on Sunday morning, Nov. 18th. Meteor rates will probably be low near midnight -- although that is a good time to see beautiful Earthgrazing Leonids -- then climb to 10 or 20 per hour by dawn. If you're lucky you might witness a storm-level outburst and count thousands of shooting stars.

With the Leonids there are no guarantees.

No matter, the coming shower will surely send some sky watchers home with life-long memories. "I'll never forget the night of Nov 18th, 2001," they might recall years from now -- just as I remember the Leonids of 1998. Others, perhaps, will gain little more than a quiet night under the stars. One thing is certain: if you stay indoors you won't see anything!

Visit SpaceWeather.com for more observing tips and for real-time updates and images during the coming meteor shower.

Web Links

2001 Leonid Forecasts - (NASA/MSFC) Leading meteor experts predict the 2001 Leonids.

Leonid Observing Tips - (SpaceWeather.com) Find out when and how to watch for the 2001 Leonids. This site includes sky maps for both of Earth's hemispheres.

Leonid Fireballs Dazzle Sky Watchers -- (Science@NASA) photos and reactions from the fiery 1998 Leonid meteor shower.

Horse Flies and Meteors -- (Science@NASA) learn more about Earth grazing meteors and find out why meteor rates are often greatest near dawn.

The Fading Milky Way - (Science@NASA) to see the greatest number of Leonids, travel to a site free from urban light pollution.

The Leonid Meteors -- Predicting spectacular meteor storms is now a remarkably exact science, with some excellent Leonid displays happening during the current few years. Visit this site from the Armagh Observatory for more information.

The Leonids -- an excellent summary of Leonid predictions and history from Gary Kronk.

Leonid MAC -- (NASA Ames) The 2001 Leonids Multiaircraft Campaign

The Moonlit Leonids 2000 -- (Science@NASA) this article, which was written just before the 2000 Leonid meteor, explains how scientists are learning to successfully forecast the Leonids.

Leonids 2000 Photo Gallery -- (SpaceWeather.com) Images and video clips of Leonid meteors observed in Nov. 2000.

Leonids Rain in Spain -- (Science@NASA) Forecasters successfully predicted a brief meteor storm over Europe and the Middle East on Nov. 18, 1999.

Leonids Galore -- (Science@NASA) Sky watchers around the globe enjoyed three predicted episodes of shooting stars on Nov. 18, 2000.


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