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134 WGN, the Journal of the IMO 28:5 (2000) The Leonids

Summary: 134 WGN, the Journal of the IMO 28:5 (2000)
The Leonids
Expectations for the 2000 Leonids
David J. Asher and Robert H. M c Naught
In the early hours (UT) of November 18, 2000, the Earth will encounter the 8-revolution old trail of meteoroids
and dust from Comet 55P/Tempel-Tuttle, and, a few hours later, the 4-revolution trail. Neither encounter will
be as close as in the cases that have given the greatest Leonid storms of the past. We discuss what is expected
from the 2000 Leonid shower, and what one can hope to learn from it.
1. Introduction
Storms or sharp outbursts occur in the Leonids, and similarly in other meteor showers, when the
Earth passes through a dust trail|a narrow structure where the spatial density of meteoroids
is very high. A new trail is generated each time an active comet returns to perihelion. Trails
soon become rather long; in the case of the Leonids, particles further forward in a trail can pass
through the ecliptic some years before particles that are further behind in the same trail.
Leonid meteors can only be produced by particles that collide with the Earth. Since all mete-
oroids in the Leonid stream have their descending node in the region of the ecliptic moderately
near where the Earth is in mid-November, in order for a meteor to be produced it is necessary
 the meteoroid reaches its node in mid-November; and
 the node is very near to the Earth's orbit.


Source: Armagh Observatory


Collections: Physics