◀ ▲ ▶History / 18th-century / Person: Piazzi, Giuseppe

Person: Piazzi, Giuseppe

Giuseppe Piazzi was a mathematician and astronomer, most famed for his discovery of Ceres between the orbits of Mars and Jupiter. He also did important work on the proper motions of stars.

Mathematical Profile (Excerpt):

• Since he is now known almost exclusively by the name Giuseppe Piazzi so we follow this standard practice.
• His parents came from one of the wealthiest families in the Lombardy region where Giuseppe was born, around 100 km north east of Milan.
• Giuseppe was so frail when he was born that his parents feared to would not survive long enough to be baptised in a church so thy baptised him at home.
• Piazzi was then sent to Sant'Andrea della Valle, the Theatines basilica in Rome, to study theology.
• While in Rome, Piazzi studied under Thomas Le Seur (1703-1770) and François Jacquier (1711-1788) who were based in the College of Trinità dei Monti.
• Piazzi was ordained a priest in 1769 and assigned to Genoa to teach philosophy.
• Piazzi and Chiaramonti were friends for the rest of their lives.
• In March 1781, Piazzi left Rome to take up an appointment as professor of mathematics at the Accademia de' Regi Studi in Palermo (which became the University of Palermo in 1806).
• As a mathematician Piazzi was knowledgeable about the latest developments in the subject and was regarded as an excellent teacher.
• The Prince of Caramanico made Piazzi professor of astronomy on 19 January 1787 and put him in charge of a project to build an observatory at Palermo.
• At this time he had little, if any, experience as an astronomer and, in recognition of this, Piazzi was given a grant to allow him to visit astronomers in France and England.
• Piazzi then went to England where he met Nevil Maskelyne, Jesse Ramsden and William Herschel.
• The most important result of Piazzi's English visit, however, was the great five-foot vertical circle, a masterpiece of eighteenth-century technology, that he commissioned from Ramsden.
• The Palermo Observatory officially opened in 1790 with Piazzi appointed as its director and, encouraged by having the accurate Palermo Circle, he set up an observing programme to take full advantage.
• This catalogue was used by William Herschel and it is likely that Piazzi had discussed it with him.
• The catalogue was known to contain inaccuracies and Piazzi, with his superior instrument, decided to obtain improved data.
• On 1 January 1801, Piazzi was working with his assistant Niccolò Cacciatore (1770-1841).
• Cacciatore had studied mathematics and physics at Palermo and began to assist Piazzi in 1798, officially becoming his assistant in 1800.
• It was made on the 1st of January, 1801, at which period the present astronomer, Cacciatore, was Piazzi's assistant in the observatory of which he is now the chief.
• As Piazzi was at that time engaged in making the noble catalogue of the stars, which has since become so well known, he placed himself at the telescope, and observed the stars as they passed the meridian, while Cacciatore wrote down the times, and the polar distances, as they were read off by his chief.
• On the third night there again occurred a discordance, and again a remark from Piazzi that an erroneous entry had probably been made by me of the place of the star.
• The way that Piazzi announced his discovery was a little strange.
• One has to assume this was sent by Piazzi (although it is just possible, but unlikely, it was sent by Cacciatore) but no name is attached.
• Lalande, the leading astronomer of the day, learnt of the discovery by reading this notice; Piazzi did not inform him personally.
• Initially Piazzi only sent letters reporting his discovery to two people, Johann Elert Bode and Barnaba Oriani, on 24 January.
• We should note that Oriani was a natural person for Piazzi to write to since the two were long term friends and collaborators.
• In 1803 Piazzi published his first catalogue of stars Praecipuarum stellarum inerrantium positiones mediae ineunte seculo XIX ex observationibus habitis in specula Panormitana ab 1792 ad annum 1802 Ⓣ(The positions of the principal fixed stars of the middle ages at the beginning of the nineteenth century from observations held in the Palermo observatory from 1792 to the year 1802).
• The Institut de France awarded Piazzi the Lalande prize for publishing the best astronomical work in 1803.
• An appendix to this catalogue contained a list of 225 stars which Piazzi claimed to have measured proper motions.
• In 1804 Piazzi sent the work Saggio sui movimenti propri delle fisse Ⓣ(Essay on the movements of the fixed stars) to the Istituto Nazionale Italiano which was based in Bologna.
• Piazzi sent his Saggio Ⓣ(Essay on the movements of the fixed stars) to the Istituto Nazionale in Bologna since they had elected him a fellow in April 1803 and, if he had been a citizen of the Cisalpine Republic, he would have received a pension being 58 years of age.
• When publication was delayed, Piazzi tried to get his Saggio Ⓣ(Essay on the movements of the fixed stars) returned to allow him to make corrections and additions.
• Piazzi's suggestion never seems to have been followed up.
• Bessel has received much praise for realising that 61 Cygni was a good candidate, but Piazzi, being the first to suggest 61 Cygni, deserves praise too.
• From 1807 Piazzi's eyesight became very poor and he had to end his days as an observer.
• The plan, although nearly the same as was pursued by M Piazzi, and therefore not altogether new, is different from the printed observations of other observatories: and is in many respects worthy of imitation.
• In 1817 Piazzi published the two-volume book Lezioni elementari di astronomia ad uso del Real Osservatorio di Palermo Ⓣ(Elementary astronomy lessons for use by the Royal Observatory of Palermo).
• Piazzi was reluctant to accept since he felt he had been treated with such kindness in Palermo.
• The king, therefore, agreed that Piazzi could be in charge of both observatories and divide his time between the two.
• He did this and in 1817 his former assistant Niccolò Cacciatore was appointed as director of the Palermo observatory while Piazzi arranged for Carlo Brioschi (1782-1833) to become the director of the Naples observatory.
• In 1824 Piazzi, now in very poor health, settled in Naples.
• Our knowledge, our capabilities, our reach and even our ambition all are far beyond what Piazzi could have imagined, and yet it is because of his discovery that we can apply them to learn more, not only about Ceres itself but also about the dawn of the solar system.

Born 16 July 1746, Ponte in Valtellina, now in Italy. Died 22 July 1826, Naples, now in Italy.

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Tags relevant for this person:

Astronomy, Origin Italy, Physics

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References

Adapted from other CC BY-SA 4.0 Sources:

1. O’Connor, John J; Robertson, Edmund F: MacTutor History of Mathematics Archive