Giuseppe Piazzi ( , ; 16 July 1746 – 22 July 1826) was an Italian
Catholic
The Catholic Church (), also known as the Roman Catholic Church, is the List of Christian denominations by number of members, largest Christian church, with 1.27 to 1.41 billion baptized Catholics Catholic Church by country, worldwid ...
priest of the
Theatine order, mathematician, and
astronomer
An astronomer is a scientist in the field of astronomy who focuses on a specific question or field outside the scope of Earth. Astronomers observe astronomical objects, such as stars, planets, natural satellite, moons, comets and galaxy, galax ...
. He established an observatory at
Palermo
Palermo ( ; ; , locally also or ) is a city in southern Italy, the capital (political), capital of both the autonomous area, autonomous region of Sicily and the Metropolitan City of Palermo, the city's surrounding metropolitan province. The ...
, now the ''
Osservatorio Astronomico di Palermo – Giuseppe S. Vaiana''. He is perhaps most famous for his discovery of the first dwarf planet,
Ceres.
Early life
No documented account of Piazzi's scientific education exists in any of the astronomer’s biographies, even the earliest ones. However, it is certain that Piazzi pursued studies in Turin, likely attending lessons by Giovan Battista Beccaria. Between 1768 and 1770, he resided at the Theatines' Home in Sant'Andrea della Valle, Rome, where he studied mathematics under François Jacquier.
In July 1770, Piazzi was appointed to the chair of Mathematics at the University of Malta. In December 1773, he moved to Ravenna, where he served as "prefetto degli studenti" and as a lecturer in Philosophy and Mathematics at the Collegio dei Nobili, a position he held until early 1779. After brief periods in Cremona and Rome, Piazzi relocated to Palermo in March 1781, taking up a role as lecturer in Mathematics at the University of Palermo (then known as the "Accademia de' Regj Studi")
He kept this position until 19 January 1787, when he became Professor of Astronomy. Almost at the same time, he was granted permission to spend two years in Paris and London, to undergo some practical training in astronomy and also to get some instruments to be specially built for the Palermo Observatory, whose foundation he was in charge of.
In the period spent abroad, from 13 March 1787 until the end of 1789, Piazzi became acquainted with the major French and English astronomers of his time and was able to have the famous altazimuthal circle made by
Jesse Ramsden
Jesse Ramsden Fellow of the Royal Society, FRS FRSE (6 October 1735 – 5 November 1800) was a British mathematician, astronomy, astronomical and scientific instrument maker. His reputation was built on the engraving and design of dividing engine ...
, one of the most skilled instrument-makers of the 18th century.
The circle was the most important instrument of the Palermo Observatory, whose official foundation took place on 1 July 1790.
In 1817,
King Ferdinand put Piazzi in charge of the completion of the
Capodimonte (Naples) Observatory, naming him General Director of the Naples and Sicily Observatories.
Astronomy career
Star cataloguing
He supervised the compilation of the Palermo Catalogue of stars, containing 7,646 star entries with unprecedented precision, including the star names "
Garnet Star" from
Herschel, and the
original
Originality is the aspect of created or invented works that distinguish them from reproductions, clones, forgeries, or substantially derivative works. The modern idea of originality is according to some scholars tied to Romanticism, by a notion t ...
Rotanev
Beta Delphini (β Delphini, abbreviated Beta Del, β Del) is a binary star in the constellation of Delphinus (constellation), Delphinus. It is the brightest star in Delphinus.
The two components of the system are desi ...
and
Sualocin. The work to observe the sky methodically. The catalogue wasn't finished for first edition publication until 1803, with a second edition in 1814.
Spurred by the success discovering Ceres (see below), and in the line of his catalogue program, Piazzi studied the proper motions of stars to find parallax measurement candidates. One of them,
61 Cygni
61 Cygni is a binary star system in the constellation Cygnus (constellation), Cygnus, consisting of a pair of K-type main-sequence star, K-type dwarf stars that orbit each other in a period of about 659 years. Of apparent magnitu ...
, was specially appointed as a good candidate for measuring a parallax, which was later performed by
Friedrich Wilhelm Bessel
Friedrich Wilhelm Bessel (; 22 July 1784 – 17 March 1846) was a German astronomer, mathematician, physicist, and geodesist. He was the first astronomer who determined reliable values for the distance from the Sun to another star by the method ...
.
On the history of the Palermo Astronomical Observatory
by Giorgia Foderà Serio The star system 61 Cygni
61 Cygni is a binary star system in the constellation Cygnus (constellation), Cygnus, consisting of a pair of K-type main-sequence star, K-type dwarf stars that orbit each other in a period of about 659 years. Of apparent magnitu ...
is sometimes still called variously ''Piazzi's Flying Star'' and ''Bessel's Star''.
The dwarf planet Ceres
Piazzi discovered Ceres. On 1 January 1801 Piazzi discovered a "stellar object" that moved against the background of star
A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...
s. At first he thought it was a fixed star, but once he noticed that it moved, he became convinced it was a planet, or as he called it, "a new star".
In his journal, he wrote:
In spite of his assumption that it was a planet, he took the conservative route and announced it as a comet
A comet is an icy, small Solar System body that warms and begins to release gases when passing close to the Sun, a process called outgassing. This produces an extended, gravitationally unbound atmosphere or Coma (cometary), coma surrounding ...
. In a letter to astronomer Barnaba Oriani of Milan
Milan ( , , ; ) is a city in northern Italy, regional capital of Lombardy, the largest city in Italy by urban area and the List of cities in Italy, second-most-populous city proper in Italy after Rome. The city proper has a population of nea ...
he made his suspicions known in writing:
He was not able to observe it long enough as it was soon lost in the glare of the Sun
The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...
. Unable to compute its orbit
In celestial mechanics, an orbit (also known as orbital revolution) is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an ...
with existing methods, the mathematician Carl Friedrich Gauss
Johann Carl Friedrich Gauss (; ; ; 30 April 177723 February 1855) was a German mathematician, astronomer, geodesist, and physicist, who contributed to many fields in mathematics and science. He was director of the Göttingen Observatory and ...
developed a new method of orbit calculation that allowed astronomers to locate it again. After its orbit was better determined, it was clear that Piazzi's assumption was correct and this object was not a comet but more like a small planet
A planet is a large, Hydrostatic equilibrium, rounded Astronomical object, astronomical body that is generally required to be in orbit around a star, stellar remnant, or brown dwarf, and is not one itself. The Solar System has eight planets b ...
. Coincidentally, it was also almost exactly where the Titius–Bode law predicted a planet would be.
Piazzi named it "Ceres Ferdinandea," after the Roman
Roman or Romans most often refers to:
*Rome, the capital city of Italy
*Ancient Rome, Roman civilization from 8th century BC to 5th century AD
*Roman people, the people of Roman civilization
*Epistle to the Romans, shortened to Romans, a letter w ...
and Sicilian goddess of grain and King Ferdinand IV of Naples
Naples ( ; ; ) is the Regions of Italy, regional capital of Campania and the third-largest city of Italy, after Rome and Milan, with a population of 908,082 within the city's administrative limits as of 2025, while its Metropolitan City of N ...
and Sicily
Sicily (Italian language, Italian and ), officially the Sicilian Region (), is an island in the central Mediterranean Sea, south of the Italian Peninsula in continental Europe and is one of the 20 regions of Italy, regions of Italy. With 4. ...
. The Ferdinandea part was later dropped for political reasons. Ceres turned out to be the first, and largest, of the asteroid
An asteroid is a minor planet—an object larger than a meteoroid that is neither a planet nor an identified comet—that orbits within the Solar System#Inner Solar System, inner Solar System or is co-orbital with Jupiter (Trojan asteroids). As ...
s existing within the asteroid belt
The asteroid belt is a torus-shaped region in the Solar System, centered on the Sun and roughly spanning the space between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies called asteroids ...
. Ceres is today called a dwarf planet
A dwarf planet is a small planetary-mass object that is in direct orbit around the Sun, massive enough to be hydrostatic equilibrium, gravitationally rounded, but insufficient to achieve clearing the neighbourhood, orbital dominance like the ...
.
Posthumous honours
Born in Italy and named in his honour was the astronomer Charles Piazzi Smyth
Charles Piazzi Smyth (3 January 1819 – 21 February 1900) was a British astronomer who was Astronomer Royal for Scotland from 1846 to 1888; he is known for many innovations in astronomy and, along with his wife Jessica Duncan Piazzi Smyth, hi ...
, son of the astronomer William Henry Smyth. In 1871, a memorial statue of Piazzi sculpted by Costantino Corti was dedicated in the main plaza of his birthplace, Ponte. In 1923, the 1000th asteroid to be numbered was named 1000 Piazzia
1000 Piazzia, provisional designation ', is a carbonaceous background asteroid from the outer region of the asteroid belt, approximately in diameter. It was discovered on 12 August 1923, by German astronomer Karl Reinmuth at Heidelberg Observat ...
in his honour. The lunar crater '' Piazzi'' was named after him in 1935. More recently, a large albedo
Albedo ( ; ) is the fraction of sunlight that is Diffuse reflection, diffusely reflected by a body. It is measured on a scale from 0 (corresponding to a black body that absorbs all incident radiation) to 1 (corresponding to a body that reflects ...
feature, probably a crater
A crater is a landform consisting of a hole or depression (geology), depression on a planetary surface, usually caused either by an object hitting the surface, or by geological activity on the planet. A crater has classically been described ...
, imaged by the Hubble Space Telescope
The Hubble Space Telescope (HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the Orbiting Solar Observatory, first space telescope, but it is one of the largest and most ...
on Ceres, has been informally named ''Piazzi''.
Works
*
See also
* Niccolò Cacciatore
Niccolò Cacciatore (; 26 January 1770 – 28 January 1841) was an Italian astronomer.
Cacciatore was born at Casteltermini, in Sicily. While studying mathematics and physics in Palermo, he became acquainted with Giuseppe Piazzi, head of the Pale ...
, his assistant and successor in the post as director
* List of Roman Catholic scientist-clerics
References
Sources
* Clifford Cunningham, Brian Marsden, Wayne Orchiston. (2011) "Giuseppe Piazzi: the controversial discovery and loss of Ceres in 1801." ''Journal for the History of Astronomy'', Volume 42.
*
*
*
External links
*
Catholic Encyclopedia entry for Giuseppe Piazzi
Giuseppe Piazzi and the Discovery of Ceres
Portrait of Giuseppe Piazzi from the Lick Observatory Records Digital Archive, UC Santa Cruz Library's Digital Collections
{{DEFAULTSORT:Piazzi, Giuseppe
1746 births
1826 deaths
People from the Province of Sondrio
18th-century Italian astronomers
Roman Catholic monks
Discoverers of asteroids
18th-century Italian Roman Catholic priests
Theatines
Ceres (dwarf planet)
Fellows of the Royal Society
Honorary members of the Saint Petersburg Academy of Sciences
Catholic clergy scientists
Academic staff of the University of Palermo
Recipients of the Lalande Prize
19th-century Italian astronomers