Catch a meteor show this weekend

By Joe Rao

Skywatching columnist

Updated: 11:51 a.m. PT Nov 17, 2006

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Mid-November brings us the return of the famous Leonid meteor shower, which has a storied history of producing some of the most sensational meteor displays ever recorded.

These meteors travel along the orbit of periodic Comet 55P/Tempel-Tuttle, and whenever that comet is passing through the inner solar system, the Leonids have a chance to provide us with a dramatic show.  But the most recent passage of the comet around the sun came back in 1998, and we are now well past the favored time frame when, for several years running, observers in various parts of the world were witnessing very strong, even storm-level Leonid activity. 

The most recent Leonid storms occurred in 2001 and 2002.

That's why this weekend, when the Leonids traditionally should be at their most numerous, we normally would expect to see no more than 10 meteors per hour, even with the promise of excellent viewing conditions thanks to a new moon on the 20th.

Still, for parts of Europe, Africa and eastern North America, a far more prolific Leonid show could be in the offing this year.

Judging the future by the past
On the morning of Nov. 17, 1969, an unexpected burst of Leonid activity was observed from parts of the eastern United States. 

Meteor rates had been rather lackluster that morning �?until quite suddenly, at around 8:50 GMT, Leonids began falling fast and furiously. Some observers reported an average of two to four meteor sightings per minute.  Peak activity apparently occurred within a few minutes of 9:00 GMT.  Then, just as abruptly as the surprising display began, it rapidly diminished until by around 9:20 GMT, things had pretty much returned to normal.

Most of the meteors that were observed were relatively faint �?although as is typical of the ultrafast Leonids, there were several brilliant meteors, leaving persistent trains in their wake that lasted for many seconds.

What caught observers off guard on that morning 37 Novembers ago was Earth's passage through a very narrow trail of dust that had been ejected from Comet Tempel-Tuttle back in 1932.  The densest part of that trail was probably about 30,000 miles (48,000 kilometers) wide, yet Earth, traveling in its orbit around the sun at 18.5 miles per second (29.8 kilometers per second), swept through it in only about a half an hour.

What to expect
In 1999, astronomers Robert McNaught and David Asher published a report concerning Leonid dust trails and cited the case of the 1969 outburst.  They also forecast that in 2006 the Earth would encounter an adjoining section of that very same dust trail from 1932. 

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The time of this year's encounter is predicted for Sunday at 4:45 GMT (11:45 p.m. ET Saturday).  Other reputable meteor forecasters such as Thomas Van Flandern of the United States, Esko Lyytinen of Finland and Jeremie Vaubaillon of France confirmed in their own Leonid studies (to within minutes of McNaught and Asher's) that Earth would indeed encounter the 1932 dust trail again in 2006.

But while another short-lived outburst seems probable this year, it likely will not be of the same intensity as what was seen in 1969.  In that year, it had been about 4.5 years since Comet Tempel-Tuttle swept past the sun.  But this November will be almost nine years since the comet last passed this way.  So when Earth interacts with that same 1932 trail this year, the particles probably won't be as thickly clustered together as they were in 1969, and the resultant display might be only about half as strong. 

Most forecasters are indicating that a sharp peak of perhaps 100 to 150 (mostly faint) Leonids per hour might be seen this year.