Temporary changes in the appearance of lunar features are known as temporary lunar phenomena, or TLP. Such occasional changes have been noted throughout human history, since the Moon is the most prominent extraterrestrial object in the sky other than the Sun and by far the more easily observed under ordinary conditions. The vast majority of TLP are probably attributable to viewing conditions at the time of observation and do not reflect actual changes on the lunar surface. Occasional reports of an anomalous brightening of large areas may be associated with solar flares. A few such phenomena have been confirmed by means of photographic film and photomultipliers.
Reports have also been made of single or successive flashes or of some steadier light that may persist for seconds or even hours. As one notable example, French astronomer Audouin Dollfus observed a glowing orangish color in the crater Langrenus in 1992 and obtained images of changes in the glow. The light was also observed by an orbiting spacecraft. Dollfus took these TLP as possible indications of gas escaping from fractures in the crater, but they have also been interpreted as visual effects rather than true TLP.