Left in the dark by moon's new hue

The light side of the moon is getting darker, but nobody seems to know why. Whether it's due to volcanic activity or dust kicked up from lunar soil, pictures from America's probe Clementine confirm that a part of the moon is darker today than it was five years ago.

The light side of the moon is getting darker, but nobody seems to know why. Whether it's due to volcanic activity or dust kicked up from lunar soil, pictures from America's probe Clementine confirm that a part of the moon is darker today than it was five years ago.

Even more perplexing, the the reddening landscape - near a crater called Aristarchus - is the same spot that was observed in 1783 by William Herschel, one of history's greatest astronomers who two years earlier had discovered the planet Uranus.

Moon watchers have reported curious flashes and fleeting clouds for centuries. Such "transient lunar phenomena", or TLP, had intrigued astronomers, but they were never confirmed, despite investigation by Nasa.

One of the most notable TLP occurred on 23 April 1994, when about 100 amateur astronomers claimed to have witnessed a darkening of the moon lasting 40 minutes near the bright lunar crater Aristarchus. At that time, the Clementine spacecraft was mapping the lunar surface. Bonnie Buratti, of Nasa's Jet Propulsion Laboratory in Pasadena, California, has examined the Clementine data and confirmed the amateurs' thoughts. "After the [1994] event, it looks redder," she told New Scientist magazine.

Winifred Cameron, a retired astronomer formerly based at the Lowell Observatory in Arizona, thinks changes may be caused by gas eruptions stirring up dust. "I'm sure that changes are due to emanations of gas that is more dense than usual," he said.

Some scientists claim that the crater contains deposits of olivine, a mineral consisting of magnesium and iron silicate that is found in volcanic rocks. That could support theories that the surface changes are due to volcanic activity.