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The Leonids

Normally this series of columns deals with upcoming celestial events but this column about a spectacular event which took place in November above your heads while most of you slept through the night of Friday the 17th into Saturday the 18th. The Leonid Meteor Shower [LMS] which has been disappointing for years was unexpectedly spectacular this year. All predictions led us to expect that this year's LMS would be inferior to last year. Worse yet, the Moon was in the way. Moonlight makes spotting small streaks very difficult.

Even so, two hearty bands of observers stationed themselves outdoors for this year's event in Charlestown. One group from Seagrave Observatory in Situate set out cameras along East Beach Road. Another slightly larger group sat on the deck of the Frosty Drew Nature Center using the building as a windbreak. It takes a hearty bunch because not only is the wind chill severe but the action doesn't start until well after midnight. Until midnight, meteors must catch the Earth from behind. After midnight, meteors meet the Earth head on. Just as a car collects more sleet pellets on the front window than on the back window as you drive, so the Earth collects more meteors in the early morning hours when it is moving into the meteor swarm.

During the peak (around 2 AM) the meteor rate exceeded 200 meteor trails per hour with 10 to 12 true fireballs. If the Moon hadn't washed out dim streaks, the rate would probably have been closer to 400 per hour. It was impossible to look at any part of the sky for more than 10 seconds without seeing a streak although most streaks started out from the constellation Leo.

Without doubt the most spectacular meteor was a large fireball which streaked out of Leo (in the East) to the North North West. The trail was at least 120 degrees long. The meteor was blue green with a blue white incandescent globe at the forward tip. This meteor was accompanied by three smaller companion meteors a close parallel trails. Almost certainly all four began as one object which shattered as it hit the upper reaches of the Earth's atmosphere. Moments later the blue green color faded to yellow and then a dark orange. We noticed the trail persisted long after other trails disappeared. We started to count seconds but the streak remained. Using an illuminated stop watch we continued to see the trail for over five minutes. Both groups of observers saw the fireball and both groups confirmed its very unusual persistence.

The source of the grains of sand and pebbles which create the LMS is detritus from the tail of the period comet Tempel-Tuttle. You may remember last years attempt to capture part dust from this Temple-Tuttle by a group of local area schools and a group from Cape Canaveral. While not successful, the attempt stirred a great deal of interest in space and astronomy in southern New England. Tempel-Tuttle makes a long oval (elliptical) orbit with one end of the orbit just inside the Earth's orbit and the far end out past Saturn. Every 33 years it makes a complete circuit, leaving dust from its tail all along its orbit. This dust remains for years until it either encounters a planet such as the Earth or it drifts slowly out of the solar system pushed by the solar wind. Eventually all the dust and gasses in Tempel-Tuttle will dissipate and the comet will cease to exist. Until then each November somewhere between the 16th and the 20th the Earth will pass though the dust trail creating yet another Leonid Meteor Shower.

The winter skies are stunning and long. Just as Spring is provides our best views of external galaxies; Summer brings our best view of the heart of our own galaxy; and Fall combines long hours with dry warm nights, so the Winter has its own specialty the saga of the creation, maturation, and termination of stars. Winter places the leading edge of one of our galaxy's arms above our heads. Here is where density waves accumulate great quantities of gas and where stars are born. Just remember to dress very warmly. Those of us who stay longest inevitably are those who wear many layers of warm clothing. The Winter sky is a special joy but only for those well insulated from its severity. We hope to see you soon some Friday evening.

Leslie Coleman
Author:
Leslie Coleman
Entry Date:
Dec 1, 2000
Published Under:
Leslie Coleman's Columns
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