April, 2003
The Leonids' Best Home Videos,
Sky & Telescope magazine
-Stuart J. Goldman

THANKS TO SOME HIGH-TECH VIDEOGRAPHY, researchers at last have freeze-frame meteor images detailed enough to probe the insides of shooting stars.

Hans Stenbaek-Nielsen (University of Alaska, Fairbanks) captured the meteors on video as part of the NASA/Ames Research Center's Leonid Multi-Instrument Aircraft Campaign (MAC). His camera, which can take video at a rate of 1,000 frames per second, was originally used to study mysterious sprites, fleeting columns of light sometimes seen above thunderstorms (S&T: January 1995, page 14).

Stationed in Alaska, Nielsen pointed the camera skyward and spent the night of November 17-18 watching a video monitor that displayed a 6°-square field. When he saw a Leonid cross the field, he stopped the recording and manually saved the hundreds of images. "I managed to save three good meteors" Nielsen says.

The video allowed Nielsen to determine that the initial pinpoint glow occurred at an altitude of 115 kilometers. Only 300 milliseconds later, at 107 km, the tiny meteoroid had developed a luminous bow shock about 600 meters (2,000 feet wide.

Leonid MAC principal investigator Peter Jenniskens (SETI Institute) explains, "Our images confirm that most meteor light comes from a bright plasma just behind the meteoroid. The images provide dimensions of the gas cloud behind the meteoroid, and tell us how long organic molecules have to endure a hot plasma before cooling down."