University Lowbrow Astronomers

The Leonids (Selected Text From Various Web Sites).

by Milton French
Printed in Reflections:  November, 1998.
Revised on September, 1999 by Dave Snyder.

From the site http://www.cyberpath.net/leonids/ [No longer accessible]

[This excerpt starts with a discussion previous Leonid meteor showers.

The Leonid meteor shower occurs every year during mid November.  Most displays are unimpressive, but every 33 years, the Leonids are more intense, sometimes with large numbers of meteors.  The Leonid showers that occurred in 1799 and 1833 were unusually active.  On November 12, 1833, residents of the United States saw so many meteors that a panic occurred.  Fortunately there were observers who remained rational.  While no one was able to accurately count them, it was estimated there were at least 240,000 meteors over the course of nine hours.  The showers of 1866 and 1867 were less active, but the astronomer Schiaparelli used these events to show that the Perseid meteor shower was associated with the comet Swift-Tuttle and the Leonid meteor shower was associated with the comet Temple-Tuttle.  The later orbits in a period of about 33 years which explains the 33 year cycle of the Leonids.

The Leonids were disappointing during the years of 1899 and 1932.  However a peak of 5000 per hour was observed during 1965 and an even bigger peak of 150,000 per hour was observed during 1966.

The excerpt then asks the question:  can satellites be damaged by Leonid meteors?  This is an important question since the Leonids are expected to be active again in both 1998 and 1999.  We really don’t know the answer, but some educated guesses can be made based on characteristics of specific satellites and predictions of meteor activity.

Predictions of Leonid activity can be made from extrapolations from previous activity or by computer simulations].

From the site:  http://www.imo.net/leohints.html (International Meteor Organization) [No longer accessible]
[This excerpt gave predictions for the 1998 Leonid meteor shower.

The International Meteor Organization (IMO) has a network of observers that hopefully will give us important information about the Leonids.  The data collected will allow us to compare expected and actual rates (during both peak and off-peak levels).

Making a prediction starts by determining the time of nodal crossing.  The time of nodal crossing is related to the time of peak of shower activity.  Other factors include the height of the radiant above the horizon at the peak time and the length of time between peak time and sunrise.  Given these factors, they predicted the best viewing would be within Northeast China.  Three maps were provided to give detailed predicted activity levels for various locations.  Predicted levels were 10,000 per hour in China, 1000 per hour in Japan with smaller levels as one gets further away from China.  However there was uncertainty in the predictions.]

From the site:  http://medicine.wustl.edu/~kronkg/leonids.html (Gary Kronk) [No longer accessible]
[The excerpt begins with an explanation of the radiant.  Meteors from the Leonid meteor shower seem to radiate from a point in the western part of the constellation of Leo and this point is called the radiant.  In order to see the maximum number of meteors, the radiant must be above the horizon.

It goes on to compare the 1833 and 1966 events.  During the evening of November 12-13, 1833 an unusual number of meteors were observed, but the most intense activity occurred in the four hours before sunrise.  The shower of November 17, 1966 was extremely active.  There were at least 30 per minute for a period of an hour and a half; the shower reached a maximum of 40 per second.]

SUMMARY - Although spectacular displays of the Leonids have been seen in the past, I think that observers in Michigan will likely be disappointed this November.  First, the month of November is the second cloudiest month of the year next to December.  The probability of clear skies is about 25-30%.  Second, we are almost exactly opposite of the area of the earth where the highest rates are most likely to be seen.  The predicted time of maximum activity is about 2:45 PM on November 17.  The closest available viewing time nearest the maximum is before sunrise on November 17.  After sunset on the 17th is the closest time to the maximum with dark skies, but the radiant is far below the horizon.  Third, there is significant uncertainty in the exact number of meteors that will be seen this year.  However, it is true that you will never succeed it you don’t try.  I still plan to look for meteors on the morning of Nov. 17 and the night of the 17-18 weather permitting.

There is a substantial amount of material available on the Internet, which should satisfy the most interested observer.  I list 6 links that I found the most useful.

[See also the 1999 Leonid Observer’s Guide.]

Links

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