Theaetetus is a lunar

impact crater An impact crater is a depression (geology), depression in the surface of a solid astronomical body formed by the hypervelocity impact event, impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal c ...

that is located to the southeast of the crater Cassini near the eastern edge of

Mare Imbrium Mare Imbrium (Latin ''imbrium'', the "Sea of Showers" or "Sea of Rains") is a vast lunar mare, lava plain within the Imbrium Basin on the Moon and is one of the larger craters in the Solar System. The Imbrium Basin formed from the collision ...

. It was named after the ancient Greek mathematician Theaetetus. It lies just to the west of the Montes Caucasus range, which forms the eastern shore of the

mare A mare is an adult female horse or other equidae, equine. In most cases, a mare is a female horse over the age of three, and a filly is a female horse three and younger. In Thoroughbred horse racing, a mare is defined as a female horse more th ...

. To the southwest is the prominent crater

Aristillus Aristyllus (; fl. c. 261 BC) was a Greek astronomer, presumably of the school of Timocharis (c. 300 BC). He was among the earliest meridian-astronomy observers. Six of his stellar declinations are preserved at Almajest 7.3. All are exa ...

. The rim of Theaetetus is distinctly

polygon In geometry, a polygon () is a plane figure made up of line segments connected to form a closed polygonal chain. The segments of a closed polygonal chain are called its '' edges'' or ''sides''. The points where two edges meet are the polygon ...

al in shape, with a slight rounding at the vertices. There is a low outer

rampart Rampart may refer to: * Rampart (fortification), a defensive wall or bank around a castle, fort or settlement Rampart may also refer to: * LAPD Rampart Division, a division of the Los Angeles Police Department ** Rampart scandal, a blanket ter ...

and a slight central rise on the crater floor, which is offset to the northeast of the crater midpoint. The interior is otherwise relatively featureless. Theaetetus lunar crater map

This crater has been noted in the past as a site of possible transient lunar phenomena. In 1902, a white cloud was observed briefly in the vicinity of the crater. Other observers, including

Patrick Moore Sir Patrick Alfred Caldwell-Moore (; 4 March 1923 – 9 December 2012) was an English amateur astronomer who attained prominence in that field as a writer, researcher, radio commentator and television presenter. Moore's early interest in astro ...

and W. H. Pickering, have also noted unusual appearances in this area.

References

* * * * * * * * * * * {{Commons category Impact craters on the Moon Mare Imbrium