PIAZZI, GIUSEPPE

PIAZZI, GIUSEPPE. — A religious of the Order of the Theatines, one of the most distinguished Italian astronomers of the early nineteenth century, born at Ponte (Valtellina) on 16 July 1746 and died at Naples on 22 July 1826.

He entered the Order of the Theatines and, having completed advanced studies in mathematics, philosophy, and theology in Rome and Milan, at the Jesuits’ Collegio di Brera, was ordained a priest and sent first to Rome (1778) as professor of philosophy, then (1780) to Palermo as professor of higher calculus. A few years later, as the fame of his learning spread, the Abbot P. was commissioned to establish an astronomical observatory in Palermo, which the city still lacked. For this purpose, after

After a journey abroad to visit the principal astronomical observatories then in existence, he chose the great tower of S. Ninfa, which dominates the entire city, and there founded an observatory that he made famous through his important work. Among this work, the first to be mentioned is the great star catalogue (the largest of all catalogues compiled by Italian astronomers), which cost P. twenty years of unremitting labor and was published in 1814 under the title Praeciparum stellarum positiones mediae, ineunte saeculo XIX, ex observationibus habitis in specula Panormitana ab anno 1792 ad annum 1812 (the 2nd ed. of the work published in 1803, completed and corrected with the new observations made from 1792 to 1813). The 1803 work published a catalogue of 6,784 stars; that of 1814 contains 7,646.

This imposing work of observation and reduction calculations immediately received the award of the Academy of Sciences of Paris; and it remains of fundamental importance, since it makes it possible to determine the “proper motions” of the stars by comparing their current positions with those determined by P. This explains why P.’s catalogue became the subject of numerous studies by the astronomers who followed him; the most recent paper on the subject is that published in 1933 by F. Porro

in the Atti della Reale Accademia d'Italia under the title Fondamenti delle riduzioni per un nuovo catalogo di stelle dedotto dalle osservazioni di G. P. a Palermo.

Other highly important investigations by P. concern the determination of the obliquity of the ecliptic and the problem of the precession of the equinoxes. But the discovery that truly made him immortal in the history of astronomy was that of the first of the minor planets situated between Mars and Jupiter, which were then completely unknown. The discovery took place on 1 January 1801, exactly at the beginning of the nineteenth century; and P. gave the new celestial body the name Ceres Ferdinandea, to recall the mythological goddess who protected the harvests of Sicily and at the same time to honor King Ferdinando I, his patron. In 1815, after the fall of Murat and the return of the Bourbon dynasty, P. was entrusted with introducing the decimal metric system into the then Kingdom of the Two Sicilies; and two years later (1817) he was summoned to Naples with the task of founding and directing the new astronomical observatory on the hill of Capodimonte, which overlooks the great city. It was there that death overtook him.