Italian astronomer who discovered (Jan. 1, 1801) and named the first asteroid, or “minor planet,” Ceres.

Piazzi became a Theatine monk in about 1764 and a professor of theology in Rome in 1779, and in 1780 he was appointed professor of higher mathematics at the Academy of Palermo. Later, with the aid of the viceroy of Sicily, he founded the Observatory of Palermo. There he produced his great catalog of the positions of 7,646 stars and demonstrated that most stars are in motion relative to the Sun. There also he discovered Ceres and the high proper motion of the important double star 61 Cygni.