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Reports of curious flashes and fleeting clouds on the Moon may
not be figments of wild imaginations, astronomers say. A new look at observations
by the American satellite Clementine show that a small area on the Moon's surface
darkened and reddened in April 1994. Why this happened remains a mystery.
For hundreds of years, people have reported seeing flashes, short-lived clouds
and other brief changes on the Moon's surface. But astronomers have never been
able to confirm the sightings. "The events were observed on many occasions,
but most astronomers don't believe in them," says Bonnie Buratti of NASA's Jet
Propulsion Laboratory in Pasadena, California.
On 23 April 1994, around a hundred amateur astronomers reported seeing a possible
darkening of the Moon, lasting 40 minutes, near the edge of the bright lunar
crater Aristarchus. At the same time, the US Department of Defense's Clementine
satellite was mapping the lunar surface.
Intrigued by the amateur reports, Buratti's team has taken a close look at the
Clementine data to see if the satellite also recorded the event. Sure enough,
they found that the crater looked different before and after the amateur reports.
"After the event, it looks redder," says Buratti, who announced the findings
at a meeting of the American Astronomical Society in Padua, Italy, last week.
Winifred Cameron, a retired astronomer who worked at the Lowell Observatory
in Arizona, thinks that brief colour changes might be caused by small gas eruptions
throwing dust around. We know that there are pockets of gas in the lunar soil,
and the gas may occasionally escape. "I'm pretty sure that some of these changes
are due to emanations of gas that are more dense than usual," says Cameron.
"The Aristarchus region is the source of about a third of all of these.
Charles Seife
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Astronomy
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