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(meteorobs) Great Expectations: The 1998 Leonid Meteor Storm
Great Expectations: The 1998 Leonid Meteor Storm
Marshall Space Flight Center Space Science News
November 10, 1998
http://science.msfc.nasadot gov/newhome/headlines/ast10nov98_1.htm
Ready or not, here they come: the 1998 Leonid meteors. On the
morning of Nov. 17, bits and pieces of periodic comet
Tempel-Tuttle will hurtle into Earth's atmosphere at a
head-spinning 158,000 mph. There is little danger - few will
reach the ground. Most will distintegrate and, in the
process, produce a "shooting star". Experts think that this
year's Leonids could rival any meteor storm this century,
with peak rates greater than 40 shooting stars per second.
Or, it could be another run-of-the-mill meteor shower. We
won't know for sure until next week.
Comet Tempel-Tuttle spends most of its time far away in the
outer solar system, between the orbits of Saturn and Uranus.
Occasionally Tempel-Tuttle pays a visit to Earth when it
swings by the sun on its 33-yr elliptical orbit. The last
time this happened was just 10 months ago, in January 1998.
The comet passed within 0.36 AU of Earth and was easily seen
with binoculars and small telescopes.
When Tempel-Tuttle comes calling, it doesn't come alone. The
comet is surrounded by a cloud of ice and dust that bubbles
off the comet's nucleus as a result of solar heating. This
debris orbits the sun along with the comet, forming a thin
elongated stream of meteoroids. The Leonid meteor stream is
several hundred million km long, but only 35,000 km wide.
Earth is scheduled to pass through the meteor stream on Nov.
17. It's a narrow target, but if we hit it just right a
historic meteor storm could result. The last time this
happened was in 1966 when as many as 100,000 shooting stars
per hour were observed at some locations. Leonids in 1966
Since 1995, when Tempel-Tuttle began its return to the inner
solar system, the November Leonids have been better than
average. In 1995 observers saw about 40 shooting stars per
hour. In 1996 and 1997, 80 per hour were seen, and in 1997
the shower lasted for over 12 hours.
Eighty shooting stars per hour is enough to excite most
experienced meteor observers, but it's nothing compared to
the potential 1998 Leonids. If the shower is anything like
the 1966 outburst, it may be possible to see hundreds of
thousands per hour. The highest rates will occur only for the
brief interval while Earth is passing through the densest
part of the Leonid meteor stream. The ribbon of comet debris
is so narrow that Earth passes through the densest part in
less than two hours.
Experts agree that the best viewing sites for the Leonids are
likely to be found in Japan, China, and other parts of east
Asia.
But what do they know?
Even though the experts are predicting the storm will occur
over east Asia, it's still worth looking if you're located
elsewhere. The experts have been wrong before, notably in
1966. In that year the Leonids were expected to occur over
Europe, but observers in North America were treated to a
spectacular shower thousands of miles away. This recollection
by James Young at JPL's Table Mountain Observatory in
California gives a sense of what the storm was like:
"This very noteworthy [1966] meteor shower was nearly missed
altogether.... There were 2-5 meteors seen every second as we
scrambled to set up the only two cameras we had, as no real
preparations had been made for any observations or
photography. The shower was expected to occur over the
European continent.
"The shower peaked around 4 a.m., with some 50 meteors
falling per second. We all felt like we needed to put on
'hard hats'! The sky was absolutely full of meteors...a sight
never imagined...and never seen since! To further understand
the sheer intensity of this event, we blinked our eyes open
for the same time we normally blink them closed, and saw the
entire sky full of streaks...everywhere!"
NASA wants you!
For this year's Leonid meteor storm Science@NASA will be
collecting observations from amateur observers, including
meteor counts, pictures, and video. We plan to use your
observations as the subject of a Science News Headline on
Nov. 18 or 19. If you would like to participate simply follow
the simple instructions (http://www.spaceweather.com/leonids.html)
about how to observe and keep
records. Then, after the shower, submit your data.
How to view the Leonids
The Leonids are best viewed during the early morning hours
between about 2 a.m. and dawn. That's when the local sky is
pointing directly into the Leonid meteor stream. Like the
parent comet, Tempel-Tuttle, the Leonid meteoroids orbit the
sun in a direction opposite to that of Earth. As a result, we
collide with the Leonids head on at high speed, nearly
158,000 mph. These high velocities are the reason that the
Leonids usually produce more fireballs than other showers.
The constellation Leo rises about 12:30 a.m. local time. The
radiant of the Leonid shower is located inside the
sickle-shaped "question mark" asterism, highlighted in the
sky map below. To find the constellation, go outside and face
east-southeast. At 3 a.m. the question-mark pattern of stars
will appear approximately 40 degrees above the horizon. The
planet Mars, posing as a bright red star, is nearby.
You won't need binoculars or a telescope, the naked eye is
usually best for seeing meteors which often streak more than
45 degrees across the sky. The field of view of most
binoculars and telescopes is simply too narrow for good
meteor observations.
Experienced meteor observers suggest the following viewing
strategy: Dress warmly as the autumn nights are likely to be
cold. Bring a reclining chair, or spread a thick blanket over
a flat spot of ground. Lie down and look up somewhat toward
the south. Meteors can appear in any part of the sky,
although their trails will tend to point back toward the
radiant.
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