Between Nov. 16 and 19, scientists will gather at Starfire to train a variety of instruments on the Leonid meteor shower. Grains of sand and dust from the comet Temple Tuttle produce these meteors. Named for the constellation Leo, from which they appear to emanate, these meteors vaporize in the Earth's atmosphere.

According to Dr. Jack Drummond, the laboratory's Directed Energy Directorate astronomer, the Leonid meteors leave behind trails which, unlike ordinary meteors that fade in a matter of seconds, can last up to an hour and are still unexplained.

"I call these lingering meteor trails 'glowworms in the sky' since they are not only visible for minutes by chemical reactions, but are twisted by the winds into serpentine shapes, appearing like snakes or worms," Drummond explained.

Scientists hope to gather enough information to explain one of the more curious atmospheric phenomena -- What makes the meteor trails glow?

The glow, called chemiluminescence, is the production of light from chemical reactions similar to bioluminsescence, the same kind of glowing reaction found in biological entities such as fireflies and their larvae, glowworms.

Drummond, who last year guided lasers onto the trails when they appeared last November, said the lingering meteor trails are self-luminescent.

"They do not shine by reflected moonlight or sunlight," he said, adding, "but the exact chemical reactions involved are unknown."

The scientists will direct a lidar, a laser that operates at visible wavelengths to gather data, onto the lingering trails. This instrument, on loan from the University of Illinois, was steered onto meteor trails last year to probe the meteors' compositions.

The data gathered by the lidar, which is attached to the 3.5-meter telescope at Starfire, indicates that although sodium may be involved in a catalytic reaction with ozone to produce sodium airglow, it is not the principle emission from the trails.

This year, additional instruments will be used to try and identify the emission lines. Three spectrographs will be aimed at the trails to try and determine the chemical reactions that are responsible for the glow.

A spectrograph divides light into a color spectrum, revealing bright (emission) and dark (absorption) lines produced by elements and molecules. The operation of two spectrographs, one from the University of Arizona and one from the University of Illinois, will study light visible to the naked eye. The third spectrograph, from Aerospace Corporation, will study light in the infrared at wavelengths that are not visible to the naked eye.

An electronic charge-coupled device camera and video camera will be used to record the changing appearance of the trails. Shown at several conferences, last year's 13-minute video, "blew the audiences away," according to Drummond. He said most people have never seen or heard of these 'glowworms in the sky' which are characteristic of the Leonid Meteor showers.

The scientists hope to answer why the 'glowworms' are peculiar to the Leonid storm periods, which occur every 33 years, and why they are rarely seen at other times. They wonder if it may imply something about the composition of the parent comet.

Although this year's shower is expected to peak over Europe on the morning of Nov. 18, it is hoped that some of the fireball components of the storm will be visible locally one or two days before or after the main peak. Here, on a dark quiet mountaintop on the southern end of Kirtland Air Force Base, N.M., scientists will be watching, waiting and hoping to unravel a mystery occurring 60 miles overhead.

Leonids 99 - Excellent overview report at sci.NASA.gov

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Toronto - October 27, 1999 -
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