A temporary event observed on the Moon’s surface, taking the form of a local abnormal brightening, obscuration, or colour change; also known as a transient lunar phenomenon (TLP). Such events have been reported by many visual observers from the time of F. W. Herschel, and have been taken as evidence of volcanic activity or outgassing at the lunar surface. However, there has been no unequivocal photographic or photometric record of such an event, and most authorities doubt their reality.