Piazzi, Giuseppe (jōzĕpˈpā pyätˈtsē) [key], 1746–1826, Italian astronomer, a Theatine priest from 1769. He became (1781) professor of mathematics at the Univ. of Palermo, supervised construction of a government observatory (opened 1791) at Palermo, and was its first director. He also established a government observatory at Naples (1817). He was the first to discover (Jan. 1, 1801) an asteroid and named it Ceres. In 1803 he published a catalog of the fixed stars, and in 1814 he enlarged it to include 7,646 stars. He wrote Lezioni elementari di astronomia (1817).