Geological Chronicle
Calippus lies on the eastern edge of the Montes Caucasus mountain range in the northern lunar hemisphere, measuring 34.03 kilometers in diameter. It sits southwest of the crater remnant Alexander and northwest of Mare Serenitatis, featuring sharp-sided interior walls and a slight exterior rampart set against the rugged mountain terrain.
The outer rim forms an irregular perimeter that bulges to the northeast and west. An interior shelf of slumped material lines the western wall, though the rest of the inner wall remains free of slumps. Along the north to east edges, the rim reaches an altitude of over 2 km, enclosing a rough interior floor that may have experienced extrusions.
Southeast of the crater along the border of Mare Serenitatis, an arcing rille named Rima Calippus extends northeast for a length of about 40 kilometers. A low-strength radar signature marks a pyroclastic deposit in the area, and observers have recorded two lunar transient phenomena at Calippus.
The crater honors the fourth-century B.C. Greek astronomer Calippus of Cyzicus. Italian astronomer Giovanni B. Riccioli introduced the name in 1651 for the feature now called Alexander, before the International Astronomical Union adopted Callippus in 1935 for this structure.