Theaetetus (crater)
 Theaetetus is a lunar impact crater that is located to the southeast of the crater Cassini near the eastern edge of Mare Imbrium. It lies just to the west of the Montes Caucasus range which forms the eastern shore of the mare. To the southwest is the prominent crater Aristillus.The rim of Theaetetus is distinctly polygonal in shape with a slight rounding at the vertices.