Great Expectations: The 1998 Leonid Meteor Storm

November 10, 1998

Ready or not, here they come: the 1998 Leonid meteors. On the morning of November 17th, bits and pieces of periodic comet Temple-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 Temple-Tuttle spends most of its time far away in the outer solar system, between the orbits of Saturn and Uranus. Occasionally Temple-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 Temple-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 one week from today, on November 17th. 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.

Since 1995, when Temple-Tuttle began its return to the inner solar system, the November Leonids has 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. The image left shows how Earth will be presented when we pass through the orbital plane of Temple-Tuttle in 1998. The best estimates suggest that the storm will occur around 1900 UT on November 17th. That's 2 p.m. on the East Coast of the US, and 11 a.m. in California.

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 November 18th or 19th. If you would like to participate simply follow the simple instructions about how to observe and keep records. Then, after the shower, return here to submit your data.

How to View the Leonids
The Leonids are best viewed during the early morning hours between about 2 am and dawn. That's when the local sky is pointing directly into the Leonid meteor stream. Like the parent comet, Temple-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.

NASA/Marshall Space Flight Center--Space Sciences Laboratory

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