The Aristarchus Anomaly
For centuries, observers have reported strange, fleeting events on the lunar surface: reddish glows, bluish mists, or sudden, star-like flashes. These "transient lunar phenomena" (LTP) have been cataloged since at least the 6th century. The area around the bright Aristarchus crater is a hot spot for these occurrences, accounting for more than one-third of all reliable sightings.
The crater itself is a bright feature on the Moon, visible to the naked eye, with an albedo, or reflectivity, nearly double that of most of the lunar surface. Historical records of phenomena here are numerous. In 1787, the famous astronomer Sir William Herschel reported seeing what he believed were three erupting volcanoes in this region. During the Apollo 11 mission in 1969, ground control alerted the crew to a report from German astronomers of a bright glow in Aristarchus. The astronauts themselves reported that the area seemed "considerably more illuminated" than its surroundings. Observations range from momentary flashes to colorful patches that can last for hours before vanishing.
Gas, Impacts, and Dust
No single explanation exists for all transient lunar phenomena, but several natural processes are considered primary causes. One hypothesis is outgassing, where gases from the Moon's interior are released through fissures in the crust. Data from the Apollo 15 and Lunar Prospector missions confirmed that radon-222 gas emanates from the Aristarchus region. This radioactive gas has a very short half-life of only 3.8 days, so its presence indicates recent or ongoing geological activity.
Many observed flashes are confirmed meteoroid impacts. Without an atmosphere to burn them up, even small objects strike the lunar surface with high velocity, creating a brief, bright flash. Since 2005, NASA's Lunar Impact Monitoring program has observed hundreds of such strikes.
A third explanation involves electrostatic effects. The solar wind continually bombards the Moon's surface, which can build up an electric charge in the fine lunar dust. This charge may be strong enough to levitate dust particles off the surface, creating temporary hazy patches that scatter sunlight in unusual ways. The transient and unpredictable nature of these events makes them difficult to study, leaving many individual sightings unexplained.