Telesto (təlĕsˈtō) [key], in astronomy, one of the named moons, or natural satellites, of Saturn. Also known as Saturn XIII (or S13), Telesto is an irregularly shaped (nonspherical) body measuring about 21 mi (34 km) by 17 mi (28 km) by 16 mi (26 km); it orbits Saturn at a mean distance of 183,093 mi (294,660 km) and has an orbital period of 1.8878 earth days—the rotational period is unknown but is assumed to be the same as the orbital period. It was discovered by Bradford A. Smith, Harold J. Reitsema, Stephen M. Larson, and John W. Fountain at the Univ of Arizona in 1980 from ground-based observations. Telesto is co-orbital with two other moons, Calypso and Tethys; that is, they orbit Saturn at the same distance. Telesto and Calypso are two of the smallest moons in the solar system.