Piazzi, Giuseppe (1746–1826)

GiuseppePiazzi was an Italian astronomer, born in Ponte di Valtellina, who became a Theatine monk, professor of theology in Rome (1779), and professor of mathematics at the Academy of Palermo (1780). He set up an observatory at Palermo in 1789, published a star catalogue (in 1803, revised in 1814) showing the positions of 7,646 stars, and discovered and named the first (and largest) asteroid, Ceres. (He proposed the name "planetaroid", but "asteroid" has prevailed.) Although he was able to make only three observations of Ceres, Carl Gauss had recently developed a mathematical technique that allowed the orbit to be calculated. Piazzi also discovered that the star 61 Cygni has a large proper motion, which led Bessel to choose it as the object of his parallax studies. The thousandth asteroid to be found was named after him.

Giuseppe Piazzi