Giuseppe Piazzi. — A religious of the Order of Theatines, one of the most illustrious Italian astronomers of the early 19th century, was born at Ponte (Valtellina) on 16 July 1746 and died at Naples on 22 July 1826.
He entered the Order of Theatines and completed advanced studies in mathematics, philosophy, and theology in Rome and Milan at the Jesuit College of Brera. He was ordained priest and was first sent to Rome (1778) as professor of philosophy, then (1780) to Palermo as professor of higher mathematics. Some years later, as his reputation for learning spread, Abbot P. was entrusted with the task of founding an astronomical observatory in Palermo, which the city still lacked.
For this purpose, after a journey abroad to visit the principal astronomical observatories then in existence, he chose the great tower of S. Ninfa, which overlooks the entire city, and there established an observatory that he made famous through his important works. Among these, first and foremost must be mentioned the great stellar catalogue (the largest of all catalogues produced by Italian astronomers), which cost P. twenty years of unremitting toil and was published in 1814 under the title *Praecipuarum stellarum positiones mediae, inerente saeculo XIX, ex observationibus habitis in specula Panormitana ab anno 1792 ad annum 1814* (this being the 2nd ed. of the work published in 1803, completed and corrected with new observations made from 1792 to 1813). The 1803 edition published the catalogue of 6,784 stars; that of 1814 contains 7,646.
This grand work of observation and reduction calculations at once won the prize of the Paris Academy of Sciences; and it remains of fundamental importance even today, since it allows the proper motions of stars to be obtained by comparing their present positions with those determined by P. This explains why P.’s catalogue became the subject of numerous studies by later astronomers; the most recent memoir 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 very important researches by P. concern the determination of the obliquity of the ecliptic and the problem of the precession of the equinoxes. But the discovery that has truly immortalized him in the history of astronomy is that of the first of the small planets lying between Mars and Jupiter, which were then completely unknown. The discovery took place on 1 January 1801, precisely at the beginning of the 19th century; and the new star was given by P. the name *Cerere Ferdinandea*, to recall the mythological protectress of the harvests of Sicily and to honour at the same time King Ferdinand I, his patron.
In 1815, after the fall of Murat and the return of the Bourbon dynasty, P. was entrusted with the introduction of the metric decimal system into the then Kingdom of the Two Sicilies, and two years later (1817) he was called to Naples to found and direct the new astronomical observatory on the hill of Capodimonte overlooking the great city. There he died.