Eugene Michel Antoniadi (1870-1944), Greek astronomer. Born in Turkey of Greek descent, Antoniadi spent most of his life in France. He gained a reputation as an astute observer of planets. Early in his career he claimed to have seen canals on the surface of Mars, although while working with a powerful telescope at the Meudon Observatory, Paris, he revised his theory, deciding the canals were an optical illusion. His detailed reports about the Martian surface laid the foundations for modern investigations. He also made observations of Mercury and Venus. He developed the Antoniadi scale of seeing conditions, still used by amateur astronomers.