it was discovered by auguste charlois on december 7, 1896, in nice. 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. the light curve for this asteroid varies "a lot" depending on the position, with the brightness variations ranging from almost zero to up to 0.2 in magnitude. dunham (2002) used 15 chords and obtained an estimated size of 171 x 138 km.