Helene [key], in astronomy, one of the named moons, or natural satellites, of Saturn. Also known as Saturn XII (or S12), Helene is an irregularly shaped (nonspherical) body measuring about 22 mi (36 km) by 20 mi (32 km) by 18 mi (30 km); it orbits Saturn at a mean distance of 234,500 mi (377,400 km) and has an orbital period of 2.7369 earth days—the rotational period is unknown but is assumed to be the same as the orbital period. It was discovered by French astronomers P. Laques and J. Lecacheaux in 1980 during ground-based observations of Saturn. Another moon, Dione, is co-orbital with Helene; that is, Helene orbits Saturn at the same distance as Dione but precedes Dione by about 60°. Before the present name was adopted, the moon was referred to as “Dione-B” and “Electra.”
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