423 Diotima (dye'-ə-tye'-mə, ; Latin Diotīma, from Greek) is a one of the largest Main belt asteroids. It is classified as a C-type asteroid and is probably composed of primitive carbonaceous material.
It was discovered by Auguste Charlois on December 7, 1896 in Nice. It is named for a priestess who was one of Socrates's teachers. It is one of seven of Charlois's discoveries that was expressly named by the Astromomisches Rechen-Institut (Astronomical Calculation Institute).
In the late 1990s, a network of astronomers worldwide gathered lightcurve data that was ultimately used to derive the spin states and shape models of 10 new asteroids, including (423) Diotima.