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Moonstruck: Caught on Video

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Dan Drollette

It's difficult to catch a falling star, and even harder to photograph one, especially if the "star" you're trying to capture is a meteoroid in the act of crashing into the moon. But Jose-Luis Ortiz and his colleagues at the Instituto de Astrofísica de Andalucía took what he said are the first photos to unequivocally show meteoroids striking the lunar surface.

And they did it with an amateur telescope and a $79.95 video camera, epitomizing the ultimate in "faster, cheaper, better."

Although the moon is pockmarked with impact craters, and the seismometers placed by Apollo astronauts have recorded evidence of many high-speed collisions, no meteoroid impacts had previously been unambiguously recorded by optical methods. A few photographs caught brief flashes of light that might have been caused by meteoroid hits, but these bright spots could have been caused by optical aberrations, cosmic rays, satellite reflections or other artifacts, Ortiz said.

To see a meteoroid hitting the moon, the astronomers needed to find an area that was bright enough for them to see a collision, but dark enough to contrast with the flash created by an impact. They aimed their telescope at the portion of the waxing moon that is in the shadow of night but that can be seen from Earth.

In the June 22 issue of Nature, he described how he and his colleagues located and videotaped the distinct flashes of five meteoroid impacts on the moon in a 90-minute period.

Ortiz, who previously worked on detecting and analyzing the collision of fragments from comet Shoemaker-Levy-9 with Jupiter, had calculated that the best time to detect any possible lunar impacts was during the Leonid meteor shower in November 1999. To see the short-lived impact flashes -- which last less than 0.02 seconds -- the team aimed a 0.2-m-diameter telescope constructed by Celestron International of Torrance, Calif., at the moon over Monterrey, Mexico. (They employed several larger research telescopes as well, including the 0.8-m Schmidt telescope of Calar Alto observatory, the 1.5-m telescope at Teide Observatory and the 0.9-m telescope at Sierra Nevada Observatory, but bad weather and technical problems intervened.)

This area was not completely dark because it was lit by our planet's reflected solar light, or what the principal investigator described as "Cinderella light." Five impacts were detected. Courtesy of J.L. Ortiz and collaborators.

To make it easier to detect these brief bursts of light, the researchers pointed the telescope away from the bright background of the moon's day side. Instead, they zeroed in on the portion of the waxing moon that faces the Earth, yet is in shadow.

For recording the impacts, the astronomers used a black-and-white PC23C CCD video camera manufactured by Supercircuits of Leander, Texas, that was hooked up to an ordinary videocassette recorder using regular videotape, which was later digitized.

Ortiz said that learning the frequency of meteoroid impacts can tell much about the nature of the solar system and can give a more accurate indication of the danger of these objects hitting man-made satellites.

Photonics Spectra
Oct 2000
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