Ever since Galileo first stared at the moon through his now-famous double-lens telescope, moon-gazers have known that craters plaster our one-and-only natural satellite. Formed as a result of high-speed impacts on the lunar surface, moon craters stand as testament to billions of years of bombardment suffered by our natural satellite.

But though scientists maintain that small meteors and other particles continue to hit the moon, no one had ever caught such an event in action -- until late last year. This week, a team of astronomers reporting in the journal Nature present the first unambiguous images of meteoroids hitting the moons surface.

Images of the Leonid impact flashes. Taken in Monterrey, Mexico, the impacts were recorded in a 90-minute time block on November 18, 1999.

"We believe this is the best candidate for recorded impact flashes [on the moon]," said Ortiz. "We had predicted that these events would be detectable from Earth in 1999...so we were not surprised to witness such an event; in fact, we were waiting for them."

According to Ortiz, his teams chance of witnessing Leonids hitting the moon was enhanced by two factors: an increased flux of the meteorites in 1999 and a favorable phase of the moon at the time of the shower. Images taken by Pedro Valdes Sada of the Universidad de Monterrey, Mexico record five impact flashes, each of which took place in less than 0.02 seconds. Sada used a 0.20-meter (7.9-inch) telescope equipped with a black-and-white, charged-couple device (CCD) video camera.

This is not this first time an impact event has been witnessed in real-time in our solar system; another prominent event occurred in 1994, when comet Shoemaker-Levy smashed into Jupiter. But these new Leonid images will help astronomers observe and study the dynamics and composition of meteoroid impacts on the moon and other bodies in the future.

In fact, it is also quite possible that similar lunar impacts may have been witnessed before last year, said Ortiz. Astronomers, including the late Sir William Herschel, have described and even photographed similar flashes of light occurring on the night side of the moon, and speculated that they may have been meteoroid impacts. "But none of these events could be confirmed by anyone else, and there is no firm conclusion that the flashes were real and not any other phenomena," said Ortiz.

Images of another possible lunar impact flash, captured by Ortiz and his colleagues on July 16, 1999.

Subsequent craters formed by the impact flashes witnessed by Ortizs team are probably between a few yards and 55 yards (50 meters) in diameter -- too small to identify because the astronomers did not determine their location with a great degree of accuracy. But according to Ortiz, future studies of lunar meteor impacts could include follow-up scans of the lunar surface, which would pinpoint newly formed craters.

"Perhaps the best strategy would be to set up several small robotic telescopes on Earth [that would be] fully devoted to searching for flashes. If a bright enough flash is captured, then the lunar orbiter might look at the area to search for new craters," explained Ortiz. "The camera of the future European Space Agency Smart 1 mission might be used to search for impact events and take closeup pictures of any such occurrences."