Theaetetus is a lunar

impact crater An impact crater is a circular depression in the surface of a solid astronomical object formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact crater ...

that is located to the southeast of the crater Cassini near the eastern edge of Mare Imbrium. It was named after the ancient Greek mathematician Theaetetus. It lies just to the west of the

Montes Caucasus Montes Caucasus is a rugged range of mountains in the northeastern part of the Moon. It begins at a gap of level surface that joins the Mare Imbrium to the west with the Mare Serenitatis to the east, and extends in an irregular band to the n ...

range, which forms the eastern shore of the

mare A mare is an adult female horse or other 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 than fo ...

. To the southwest is the prominent crater Aristillus. The rim of Theaetetus is distinctly

polygon In geometry, a polygon () is a plane figure that is described by a finite number of straight line segments connected to form a closed ''polygonal chain'' (or ''polygonal circuit''). The bounded plane region, the bounding circuit, or the two to ...

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: * "O'er the Ramparts We Watched" is a key line from "The Star-Spangled Banner", the national anthem of the ...

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 and

W. H. Pickering William Henry Pickering (February 15, 1858 – January 16, 1938) was an American astronomer. Pickering constructed and established several observatories or astronomical observation stations, notably including Percival Lowell's Flagstaff Obser ...

, have also noted unusual appearances in this area.

References

* * * * * * * * * * * {{Commonscat Impact craters on the Moon Mare Imbrium