Editing Giuseppe Piazzi (section)

==Astronomy career==

===Star cataloguing===

He supervised the compilation of the Palermo Catalogue of stars, containing 7,646 star entries with unprecedented precision,<ref>[http://www.daviddarling.info/encyclopedia/P/Piazzi.html DavidDarling.com: Piazzi, Giuseppe (1746–1826)]</ref> including the star names "[[Mu Cephei|Garnet Star]]" from [[William Herschel|Herschel]], and the [[Sualocin and Rotanev|original]] [[Rotanev]] 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.{{sfn|Fox|1913}}

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]], was specially appointed as a good candidate for measuring a parallax, which was later performed by [[Friedrich Wilhelm Bessel]].<ref>[http://www.astropa.unipa.it/HISTORY/history.htm On the history of the Palermo Astronomical Observatory] by Giorgia Foderà Serio</ref> The star system [[61 Cygni]] is sometimes still called variously ''Piazzi's Flying Star'' and ''Bessel's Star''.

===The dwarf planet Ceres===
{{unref-section|date=February 2021}}
[[File:Ceres-Beobachtung von Piazzi.png|thumb|Piazzi's observations published in the [[:de:Monatliche Correspondenz|Monatliche Correspondenz]], September 1801]]

Piazzi discovered [[1 Ceres|Ceres]]. On 1 January 1801 Piazzi discovered a "stellar object" that moved against the background of [[star]]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: {{quote|The light was a little faint, and of the colour of [[Jupiter]], but similar to many others which generally are reckoned of the eighth [[Apparent magnitude|magnitude]]. Therefore I had no doubt of its being any other than a fixed star. In the evening of the second I repeated my observations, and having found that it did not correspond either in time or in distance from the zenith with the former observation, I began to entertain some doubts of its accuracy. I conceived afterwards a great suspicion that it might be a new star. The evening of the third, my suspicion was converted into certainty, being assured it was not a fixed star. Nevertheless before I made it known, I waited till the evening of the fourth, when I had the satisfaction to see it had moved at the same rate as on the preceding days.}}

In spite of his assumption that it was a planet, he took the conservative route and announced it as a [[comet]]. In a letter to astronomer [[Barnaba Oriani]] of [[Milan]] he made his suspicions known in writing:

{{quote|I have announced this star as a comet, but since it is not accompanied by any nebulosity and, further, since its movement is so slow and rather uniform, it has occurred to me several times that it might be something better than a comet. But I have been careful not to advance this supposition to the public.}}

He was not able to observe it long enough as it was soon lost in the glare of the [[Sun]]. Unable to compute its [[orbit]] with existing methods, the mathematician [[Carl Friedrich Gauss]] 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]]. Coincidentally, it was also almost exactly where the [[Titius–Bode law]] predicted a planet would be.

Piazzi named it "Ceres Ferdinandea," after the [[Roman mythology|Roman]] and Sicilian [[Ceres (Roman mythology)|goddess of grain]] and [[Ferdinand I of the Two Sicilies|King Ferdinand IV]] of [[Naples]] and [[Sicily]]. The Ferdinandea part was later dropped for political reasons. [[Ceres (dwarf planet)|Ceres]] turned out to be the first, and largest, of the [[asteroid]]s existing within the [[asteroid belt]]. Ceres is today called a [[dwarf planet]].