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History

Discovery

Piazzi's book "Della scoperta del nuovo pianeta Cerere Ferdinandea" outlining the discovery of Ceres, dedicated the new "planet" to Ferdinand I of the Two Sicilies.

Johann Elert Bode, in 1772, first suggested that an undiscovered planet could exist between the orbits of Mars and Jupiter.<ref name="hoskin" /> Kepler had already noticed the gap between Mars and Jupiter in 1596.<ref name="hoskin" /> Bode based his idea on the Titius–Bode law—a now-discredited hypothesis Johann Daniel Titius first proposed in 1766—observing that there was a regular pattern in the semi-major axes of the orbits of known planets, marred only by the large gap between Mars and Jupiter.<ref name="hoskin" /><ref name="Hogg1948">{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref> The pattern predicted that the missing planet ought to have an orbit with a semi-major axis near 2.8 astronomical units (AU).<ref name="Hogg1948" /> William Herschel's discovery of Uranus in 1781<ref name="hoskin" /> near the predicted distance for the next body beyond Saturn increased faith in the law of Titius and Bode, and in 1800, a group headed by Franz Xaver von Zach, editor of the Monatliche Correspondenz, sent requests to twenty-four experienced astronomers (dubbed the "celestial police"), asking that they combine their efforts and begin a methodical search for the expected planet.<ref name="hoskin" /><ref name="Hogg1948" /> Although they did not discover Ceres, they later found several large asteroids.<ref name="Hogg1948" />

One of the astronomers selected for the search was Giuseppe Piazzi at the Academy of Palermo, Sicily. Before receiving his invitation to join the group, Piazzi discovered Ceres on 1 January 1801.<ref>{{#invoke:citation/CS1|citation |CitationClass=book }}</ref> He was searching for "the 87th [star] of the Catalogue of the Zodiacal stars of Mr la Caille", but found that "it was preceded by another".<ref name="hoskin">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Instead of a star, Piazzi had found a moving star-like object, which he first thought was a comet.<ref name="Forbes1971">{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref> Piazzi observed Ceres a total of 24 times, the final time on 11 February 1801, when illness interrupted his observations. He announced his discovery on 24 January 1801 in letters to only two fellow astronomers, his compatriot Barnaba Oriani of Milan and Bode of Berlin.<ref>{{#invoke:citation/CS1|citation |CitationClass=book }}</ref> He reported it as a comet but "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".<ref name="hoskin" /> In April, Piazzi sent his complete observations to Oriani, Bode, and Jérôme Lalande in Paris. The information was published in the September 1801 issue of the Monatliche Correspondenz.<ref name="Forbes1971" />

By this time, the apparent position of Ceres had changed (mostly due to Earth's orbital motion), and was too close to the Sun's glare for other astronomers to confirm Piazzi's observations. Toward the end of the year, Ceres should have been visible again, but after such a long time it was difficult to predict its exact position. To recover Ceres, Carl Friedrich Gauss, then 24 years old, developed an efficient method of orbit determination.<ref name="Forbes1971" /> In only a few weeks, he predicted the path of Ceres and sent his results to von Zach. On 31 December 1801, von Zach and Heinrich W. M. Olbers found Ceres near the predicted position and thus recovered it.<ref name="Forbes1971" />

The early observers were only able to calculate the size of Ceres to within an order of magnitude. Herschel underestimated its diameter as 260 km in 1802, whereas in 1811 Johann Hieronymus Schröter overestimated it as 2,613 km.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name="Hughes1994">{{#invoke:Citation/CS1|citation |CitationClass=journal }}(Page 335)</ref>

Name

Piazzi originally suggested the name Cerere Ferdinandea for his discovery, after the goddess Ceres (Roman goddess of agriculture, Cerere in Italian, who was believed to have originated in Sicily and whose oldest temple was there) and King Ferdinand of Sicily.<ref name="hoskin" /><ref name="Forbes1971" /> "Ferdinandea", however, was not acceptable to other nations and was dropped. Ceres was called Hera for a short time in Germany.<ref>{{#invoke:citation/CS1|citation |CitationClass=book }}</ref> In Greece, it is called Demeter (Δήμητρα), after the Greek equivalent of the Roman Cerēs;<ref group="lower-alpha">All other languages but one use a variant of Ceres/Cerere: Russian Tserera, Persian Seres, Japanese Keresu. The exception is Chinese, which uses 'grain-god(dess) star' (穀神星 gǔshénxīng). Note that this is unlike the goddess Ceres, where Chinese does use the Latin name (刻瑞斯 kèruìsī).</ref> in English, that name is used for the asteroid 1108 Demeter.

The regular adjectival forms of the name are Cererian and Cererean,<ref>{{#invoke:citation/CS1|citation |CitationClass=book }}</ref> derived from the Latin genitive Cereris,<ref name="Simpson1979" /> but Ceresian is occasionally seen for the goddess (as in the sickle-shaped Ceresian Lake), as is the shorter form Cerean.

The old astronomical symbol of Ceres is a sickle, (Sickle variant symbol of Ceres),<ref>Unicode value U+26B3</ref> similar to Venus's symbol but with a break in the circle. It has a variant Cee variant symbol of Ceres , reversed under the influence of the initial letter 'C' of 'Ceres'. These were later replaced with the generic asteroid symbol of a numbered disk, .<ref name="Forbes1971" /><ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref>

Cerium, a rare-earth element discovered in 1803, was named after Ceres.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>Unknown extension tag "ref" In the same year another element was also initially named after Ceres, but when cerium was named, its discoverer changed the name to palladium, after the second asteroid, 2 Pallas.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Classification

The categorization of Ceres has changed more than once and has been the subject of some disagreement. Johann Elert Bode believed Ceres to be the "missing planet" he had proposed to exist between Mars and Jupiter, at a distance of 419 million km (2.8 AU) from the Sun.<ref name="hoskin" /> Ceres was assigned a planetary symbol, and remained listed as a planet in astronomy books and tables (along with 2 Pallas, 3 Juno, and 4 Vesta) for half a century.<ref name="hoskin" /><ref name="Forbes1971" /><ref name="Hilton" />

Sizes of the first ten main-belt objects discovered profiled against the Moon. Ceres is far left (1).

As other objects were discovered in the neighborhood of Ceres, it was realized that Ceres represented the first of a new class of objects.<ref name="hoskin" /> In 1802, with the discovery of 2 Pallas, William Herschel coined the term asteroid ("star-like") for these bodies,<ref name="Hilton">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> writing that "they resemble small stars so much as hardly to be distinguished from them, even by very good telescopes".<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> As the first such body to be discovered, Ceres was given the designation 1 Ceres under the modern system of minor-planet designations. By the 1860s, the existence of a fundamental difference between asteroids such as Ceres and the major planets was widely accepted, though a precise definition of "planet" was never formulated.<ref name="Hilton" /> {{#invoke:Multiple image|render}} The 2006 debate surrounding Pluto and what constitutes a planet led to Ceres being considered for reclassification as a planet.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=news }}</ref> A proposal before the International Astronomical Union for the definition of a planet would have defined a planet as "a celestial body that (a) has sufficient mass for its self-gravity to overcome rigid-body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (b) is in orbit around a star, and is neither a star nor a satellite of a planet".<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Had this resolution been adopted, it would have made Ceres the fifth planet in order from the Sun.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> This never happened, however, and on 24 August 2006 a modified definition was adopted, carrying the additional requirement that a planet must have "cleared the neighborhood around its orbit". By this definition, Ceres is not a planet because it does not dominate its orbit, sharing it as it does with the thousands of other asteroids in the asteroid belt and constituting only about a third of the mass of the belt. Bodies that met the first proposed definition but not the second, such as Ceres, were instead classified as dwarf planets.

Ceres is the largest object in the asteroid belt.<ref name="Rivkin2006" /> It is sometimes assumed that Ceres has been reclassified as a dwarf planet, and that it is therefore no longer considered an asteroid. For example, a news update at Space.com spoke of "Pallas, the largest asteroid, and Ceres, the dwarf planet formerly classified as an asteroid",<ref>Geoff Gaherty, "How to Spot Giant Asteroid Vesta in Night Sky This Week", 3 August 2011 How to Spot Giant Asteroid Vesta in Night Sky This Week | Asteroid Vesta Skywatching Tips | Amateur Astronomy, Asteroids & Comets | Space.com Archived at WebCite</ref> whereas an IAU question-and-answer posting states, "Ceres is (or now we can say it was) the largest asteroid", though it then speaks of "other asteroids" crossing Ceres's path and otherwise implies that Ceres is still considered an asteroid.<ref name="IAU-QA">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The Minor Planet Center notes that such bodies may have dual designations.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The 2006 IAU decision that classified Ceres as a dwarf planet never addressed whether it is or is not an asteroid. Indeed, the IAU has never defined the word 'asteroid' at all, having preferred the term 'minor planet' until 2006, and preferring the terms 'small Solar System body' and 'dwarf planet' after 2006. Lang (2011) comments "the [IAU has] added a new designation to Ceres, classifying it as a dwarf planet. ... By [its] definition, Eris, Haumea, Makemake and Pluto, as well as the largest asteroid, 1 Ceres, are all dwarf planets", and describes it elsewhere as "the dwarf planet–asteroid 1 Ceres".<ref>{{#invoke:citation/CS1|citation |CitationClass=book }}</ref> NASA continues to refer to Ceres as an asteroid,<ref>NASA/JPL, Dawn Views Vesta, 2 August 2011 Archived at WebCite ("Dawn will orbit two of the largest asteroids in the Main Belt").</ref> as do various academic textbooks.<ref>{{#invoke:citation/CS1|citation |CitationClass=book }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=book }}</ref>


Ceres (dwarf planet) sections
Intro  History  Physical characteristics  Orbit  Origin and evolution  Potential habitability  Observation  Exploration  Maps  Gallery  See also  Notes  References  External links  

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