A transient lunar phenomenon (TLP) or lunar transient phenomenon (LTP) is a short-lived change in light, color or appearance on the surface of the Moon. The term was created by Patrick Moore in his co-authorship of NASA Technical Report R-277 Chronological Catalog of Reported Lunar Events, published in 1968.
Claims of short-lived lunar phenomena go back at least 1,000 years, with some having been observed independently by multiple witnesses or reputable scientists. Nevertheless, the majority of transient lunar phenomenon reports are irreproducible and do not possess adequate control experiments that could be used to distinguish among alternative hypotheses to explain their origins.
Most lunar scientists will acknowledge that transient events such as outgassing and impact cratering do occur over geologic time. The controversy lies in the frequency of such events.
Description of events Reports of transient lunar phenomena range from foggy patches to permanent changes of the lunar landscape. Cameron classifies these as (1) gaseous, involving mists and other forms of obscuration, (2) reddish colorations, (3) green, blue or violet colorations, (4) brightenings, and (5) darkening. Two extensive catalogs of transient lunar phenomena exist, with the most recent tallying 2,254 events going back to the 6th century. Of the most reliable of these events, at least one-third come from the vicinity of the Aristarchus plateau.
An overview of the more famous historical accounts of transient phenomena include the following:
Pre 1700 On June 18, 1178, five or more monks from Canterbury reported an upheaval on the Moon shortly after sunset: This description appears outlandish, perhaps due to the writer's and viewers' lack of understanding of astronomical phenomena. In 1976, Jack Hartung proposed that this described the formation of the Giordano Bruno crater. However, more recent studies suggest that it appears very unlikely the 1178 event was related to the formation of Crater Giordano Bruno, or was even a true transient lunar phenomenon at all. The millions of tons of lunar debris ejected from an impact large enough to leave a 22-km-wide crater would have resulted in an unprecedentedly intense, week-long meteor storm on Earth. No accounts of such a memorable storm have been found in any known historical records, including several astronomical archives from around the world.Kettlewell, Jo (1 May 2001). "Historic lunar impact questioned". BBC. Retrieved 13 July 2013. In light of this, it is suspected that the group of monks (the event's only known witnesses) saw the atmospheric explosion of a directly oncoming meteor in chance alignment, from their specific vantage point, with the far more distant Moon."The Mysterious Case of Crater Giordano Bruno". NASA. Retrieved 13 July 2013. On November 26, 1540, a transient phenomenon appeared between Mare Serenitatis and Mare Imbrium. This event is depicted on a contemporary woodcut.Barbara M. Middlehurst, An Analysis of Lunar Events, Reviews of Geophysics, May 1967, Vol.5, N°2, page 173
1701–1800 On the evening of August 16, 1725, the Italian astronomer Francesco Bianchini saw a reddish light streak across the floor of crater Plato, "like a bar stretching straight from one end to the other" along the major axis of the foreshortened elliptical shape of the crater.Bianchini, Observations concerning the planet Venus, translated by Sally Beaumont, Springer, 1996, p. 23, from Bianchini, Hesperi et phosphori nova phaenomena, Rome, 1728, pp. 5–6 During the night of April 19, 1787, the British astronomer Sir William Herschel noticed three red glowing spots on the dark part of the Moon.Herschel, W. (1956, May). Herschel’s ‘Lunar volcanos.’ Sky and Telescope, pp. 302–304. (Reprint of An Account of Three Volcanos in the Moon, William Herschel’s report to the Royal Society on April 26, 1787, reprinted from his Collected Works (1912)) He informed King George III and other astronomers of his observations. Herschel attributed the phenomena to erupting volcanoes and perceived the luminosity of the brightest of the three as greater than the brightness of a comet that had been discovered on April 10. His observations were made while an aurora borealis (northern lights) rippled above Padua, Italy. Aurora activity that far south from the Arctic Circle was very rare. Padua's display and Herschel's observations had happened a few days before the number of sunspots had peaked in May 1787. In December 1787, a luminous point was seen by a Maltese observer named d'Angos.K.E.Chilton, Journal of the Royal Astronomical Society of Canada, Vol.63, page 203 On September 26, 1789, the German astronomer Johann Hieronymus Schröter noticed a speck of light close to the eastern foot of the Montes Alpes. It was seen on the night side of the Moon and appeared like a star of Magnitude 5 to the naked eye.T.W.Webb, Celestial Objects for Common Telescopes, Volume 1: The Solar System, page 113 On October 15, 1789, J.H.Schröter observed two bright bursts of light, each one of them composed of many single, separate small sparks, appearing on the night side of the Moon near crater Plato and Mare Imbrium.K.Bispham, Schröter and Lunar Transient Phenomena, Journal of the British Astronomical Association, 78:381, 1968 In 1790, Sir William Herschel saw one or more star-like appearances on the eclipsed Moon. On November 1–2, 1791, J.H.Schröter noticed the bowl-shaped crater Posidonius A on the floor of crater Posidonius without internal shadow.A.J.M.Wanders, Op Ontdekking in het Maanland, blz 352 In 1794, a report circulated that it was possible to see a volcano on the Moon with the naked eye.
1801–1900 Between 1830 and 1840, the German astronomer Johann Heinrich von Mädler observed a strong reddish tint closely east of crater Lichtenberg in Oceanus Procellarum.Harold Hill, A Portfolio of Lunar Drawings, page 94 See also Barcroft in 1940, Haas at a later date, Baum in 1951, and Hill in 1988. On November 24, 1865, Williams and two others observed for one hour and a half a distinct bright speck like an 8 magnitude star on the dark side near crater Carlini in Mare Imbrium.T.W.Webb: Celestial Objects for Common Telescopes, Volume 1: The Solar System, page 125 (lunar crater N°128: Carlini). In 1866, the experienced lunar observer and mapmaker J. F. Julius Schmidt claimed that the Linné crater had changed its appearance. Based on drawings made earlier by J. H. Schröter, as well as personal observations and drawings made between 1841 and 1843, he stated that the crater "at the time of oblique illumination cannot at all be seen" (his emphasis), whereas at high illumination, it was visible as a bright spot. Based on repeat observations, he further stated that "Linné can never be seen under any illumination as a crater of the normal type" and that "a local change has taken place". Today, Linné is visible as a normal young impact crater with a diameter of about 1.5 miles (2.4 km). On January 4, 1873, French astronomer Étienne Léopold Trouvelot observed crater Kant which was "filled with mist".Patrick Moore: New Guide to the Moon, page 289 On August 31, 1877, English amateur astronomer Arthur Stanley Williams noticed some sort of phosphorescent glow on the shadowed southern part of the walled plain named Plato.A.J.M.Wanders, Op Ontdekking in het Maanland, blz 356 On August 6–7, 1881, German astronomer Hermann Joseph Klein observed the region of craters Aristarchus and Herodotus, and noticed a strong violet glare with some sort of nebulosity.A.J.M.Wanders, Op Ontdekking in het Maanland, blz 159 On March 27, 1882, A.S.Williams saw the floor of Plato at sunrise "glowing with a curious milky kind of light".A.J.M.Wanders, Op Ontdekking in het Maanland, blz 356. V.A.Firsoff, The Old Moon and the New, page 183 On July 3, 1882, several residents of Lebanon, Connecticut, observed two pyramidal luminous protuberances on the Moon's upper limb. They were not large, but gave the Moon a look strikingly like that of a horned owl or the head of an English bull terrier."A Curious Appearance of the Moon", Scientific American, 46:49, 1882 On February 19, 1885, Gray saw a small crater near the larger crater Hercules glow dull red "with vivid contrast".V.A.Firsoff, The Old Moon and the New, page 185 On February 21, 1885, Knopp observed red patches in crater Cassini. In 1887, French amateur astronomer and selenographer Casimir Marie Gaudibert noticed a temporary white spot in the central part of crater Herodotus.Harry De Meyer, Maanmonografieën P.72, Vereniging Voor Sterrenkunde (VVS), 1969 One night in 1892, American astronomer Edward Emerson Barnard found the bowl of crater Thales filled with luminous haze. 1891–1897, American astronomer William Henry Pickering gives drawings of a probable eruption of steam from crater Schröter.T.W.Webb, Celestial Objects for Common Telescopes, Volume 1: The Solar System, page 161 A photograph made on August 26, 1898, through the équatorial coudé, shows bowl-shaped craterlet Posidonius C on the floor of crater Posidonius as a bright spot without shadow, although the terminator (day-night boundary) was nearby.A.J.M.Wanders, Op Ontdekking in het Maanland, blz 354
1901–1950 A photograph made on September 30, 1901, through the équatorial coudé, shows bowl-shaped craterlet Posidonius C as an elongated bright spot without shadow, although the photograph was made shortly before sunset at crater Posidonius. In 1902, French astronomer Albert Charbonneaux, using the Meudon 33-inch refractor telescope at the Paris Observatory, noticed a small white cloud west of crater Theaetetus.Patrick Moore, New Guide to the Moon, page 203 In 1905, German astronomer Friedrich Simon Archenhold observed a bright spot at the location of the bowl-shaped craterlet Posidonius C on the floor of crater Posidonius.A.J.M.Wanders, Op Ontdekking in het Maanland, blz 353 On May 19, 1912, Austrian astronomer and rocketry pioneer Max Valier noticed a small red glowing area on the Moon's night side. In January 1913, William Henry Pickering observed the last one of a series of eruptions of some sort of white material at crater Eimmart."Change in a Lunar Crater", American Journal of Science, 4:38:95, 1914 On June 15, 1913, the British civil engineer and astronomer William Maw observed a 'small reddish spot' in crater South.V.A.Firsoff, The Old Moon and the New, page 185. T.W.Webb, Celestial Objects for Common Telescopes, Volume 1: The Solar System, page 163 On February 22, 1931, Joulia observed a reddish glow in crater Aristarchus. In the same year (1931) and at the same location, British businessman and amateur astronomer Walter Goodacre and (?) Molesworth (1931?) observed a bluish 'glare'. Percy B. Molesworth ? (1867–1908). On June 17, 1931, N.J.Giddings and his wife observed unusual flashes of light (lightning-like phenomena) on the night side of the Moon.N.J.Giddings, "Lightning-like phenomena on the Moon", Science, 104:146, 1946 On August 2, 1939, British observer Patrick Moore noticed that the internal detail of the walled plain Schickard was obliterated by an extensive mist.V.A.Firsoff, The Old Moon and the New, page 183 In 1940, American amateur astronomer David P. Barcroft (1897–1974) observed a pronounced reddish-brown color near crater Lichtenberg in Oceanus Procellarum. See also J.H.Mädler between 1830 and 1840, Baum in 1951, and Hill in 1988. On July 10, 1941, American amateur astronomer Walter H. Haas noticed a moving dot of white light near crater Hansteen in the southern section of Oceanus Procellarum.Harry de Meyer, Maanmonografieën, blz 67, Vereniging Voor Sterrenkunde (VVS), 1969 On August 31, 1944, the floor of the walled plain Schickard looked misty to the Welsh-born engineer and amateur astronomer Hugh Percy Wilkins. Some minor craters in it, which are normally well shadowed, stood out as white spots under a low sun.