[重要] [新闻] 2002年的狮子座流星雨（英文）

The Truth about the 2002 Leonid Meteor Storm
NASA Science News

Another Leonid meteor storm is due in 2002. Rumor has it that a full Moon
will ruin the show ... but maybe not.

May 10, 2002: When the Sun rose on November 19, 2001, I was standing
outdoors gaping at the sky. It was cold at 9000 ft. altitude where I live,
and my neck was stiff because I had been staring upwards for about six
hours. But none of that mattered. I was spellbound by the biggest meteor
storm in decades.

All night long Leonid meteors had streaked across the sky -- thousands of
them. Even as the horizon brightened at dawn, I could still see fireballs
flashing in the distance. There was only one thought on my mind when the
night sky finally vanished:

"I can't wait until next year."

The Leonid meteor shower happens every year in mid-November. That's when our
planet has a close encounter with Comet Tempel-Tuttle's orbit -- a region of
space littered with streams of comet dust. Usually we pass through the
rarefied gaps between streams and sky watchers see no more than 10 or 15
Leonids per hour. But sometimes (like last year) Earth plows through a
debris stream more or less head-on and a full-fledged meteor storm erupts.

Such meteor storms rarely happen in consecutive years, but 2001 and 2002 are
exceptions. Experts have just released their predictions: Depending on where
you live (Europe and the Americas are favored) Leonid meteor rates in 2002
should equal or exceed 2001 levels.

That's the good news. The bad news is that the Moon will be full when the
storm begins on Nov. 19th. Glaring moonlight will completely overwhelm many
faint shooting stars. Indeed, I often hear that the Moon is going to "ruin
the show."

I doubt it.

Moonlight will indeed reduce the number of visible meteors by some factor
between 2 and 5, but that's not enough to wipe out a storm of bright
Leonids. If predictions are correct, peak rates this year would reach 5,000
to 10,000 meteors per hour under ideally dark skies. Even if the Moon's
glare obliterates all but a thousand of those, it's still a marvelous show
-- one of the best in decades.

Furthermore, there are steps you can take to minimize lunar glare. First,
don't stare at the Moon. Face away from it; look toward the darkest part of
the sky. If possible, choose an observing site where you can stand in the
shadow of a building or some other Moon-baffle.

Second, travel if necessary to a place where the air is dry and clear. Even
when you face away from the Moon the air glows because of moonlight
scattered from air molecules and aerosols (e.g., water droplets, dust and
pollution). The glow will be less in places where the air is dry and
pollution-free. Mountaintops are excellent because they rise above the humid
lower atmosphere and most aerosols.

Another place to escape Moon-glow is on board an airliner. A commercial jet
flying at 33,000 feet (10 km), for example, is above 75% of Earth's
light-scattering atmosphere. Meteors disintegrate much higher than that,
about 80 km above Earth's surface, so watching the storm from an airplane is
not dangerous. However, there are other problems: Airplane windows are small
and blurry, and you'll have to convince someone to turn off the cabin
lights.

For most sky watchers, the ground is a better choice. But when and where?

This year on Nov. 19th, Earth will pass through two of Comet Tempel-Tuttle's
debris streams. The first encounter should cause a flurry of meteors over
Europe and Africa around 0430 UT. The second encounter favors North
Americans who are likely to see an outburst around 5:30 a.m. EST or 10:30
UT. (Note: UT is Universal Time, also known as Greenwich Mean Time.)

The timing is good news for meteor watchers in western Europe and eastern
North America. When the flurries begin shortly before local dawn, the
bothersome Moon will be setting. In New York, for example, the Moon will lie
only six degrees above the western horizon during the predicted peak.
Meanwhile, the constellation Leo (from which Leonid meteors stream) will be
high in the southern sky, well away from the sinking Moon.

Many observers plan to visit the American southwest to see the Leonids. The
Moon will be higher there when the storm erupts at 2:30 to 3:30 a.m. local
time. Nevertheless, there are many high-altitude sites in that part of North
America with dry, clear air -- and thus relatively little Moon-glow.

No matter where you plan to be -- on a mountaintop, in an airplane or at
home in the city -- don't miss the 2002 Leonids. Earth won't plow head-on
into another Leonid debris stream for decades. The Moon will be a nuisance
this year, but not enough to ruin the show if the Leonids are as bright and
numerous as they were in 2001.

When the Sun rises on Nov. 19, 2002, I hope to be outside again,
stiff-necked and spellbound ... just like last year.