Transient lunar phenomenon

Transient lunar phenomena are short-lived changes reported in the appearance of a localized area of the Moon. Historical reports include brightenings, reddish or bluish color changes, and hazy or darkened features. Authors use both “transient lunar phenomenon” (TLP) and “lunar transient phenomenon” (LTP); the abbreviation TLP is common. These descriptions refer to reported observations, not to one established physical mechanism.

Astronomers have assembled historical catalogues of reported events and have examined their distribution and repeatability. A review by Arlin Crotts found that reports cluster around some lunar features, while also emphasizing observer effects, terrestrial atmospheric effects, and the unsettled nature of the phenomenon. Some reports may be attributable to known events such as meteoroid impacts or observational conditions; other explanations, including transient lunar outgassing, have been investigated. The evidence does not establish a single explanation for all reports, and the category should not be treated as proof of ongoing lunar volcanism.

Careful observations require recording time, location on the lunar disk, viewing and atmospheric conditions, instrument details, and independent confirmation where possible. Systematic monitoring and instrument-based measurements can help distinguish real changes at the Moon from effects in Earth’s atmosphere, optical equipment, or human perception. NASA’s historical cataloguing work documents many reported observations, but a catalogue entry is not by itself confirmation of a physical event or its cause.