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Nomenclature

The ancients knew Mercury by different names depending on whether it was an evening star or a morning star. By about 350 BC, the ancient Greeks had realized the two stars were one. They knew the planet as Στίλβων Stilbōn, meaning "twinkling", and Ἑρμής Hermēs, for its fleeting motion, a name that is retained in modern Greek (Ερμής Ermis). The Romans named the planet after the swift-footed Roman messenger god, Mercury (Latin Mercurius), whom they equated with the Greek Hermes, because it moves across the sky faster than any other planet. The astronomical symbol for Mercury is a stylized version of Hermes' caduceus; a Christian cross was added in the 16th century:.