The Asteroid Belt
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The asteroid belt is the region of the Solar System located roughly between the orbits of the planets Mars and Jupiter. It is occupied by numerous irregularly shaped bodies called asteroids or minor planets. The asteroid belt is also termed the main asteroid belt or main belt to distinguish its members from other asteroids in the Solar System such as near-Earth asteroidsand trojan asteroids. About half the mass of the belt is contained in the four largest asteroids, Ceres, Vesta, Pallas, andHygiea. Vesta, Pallas, and Hygiea have mean diameters of more than 400 km, whereas Ceres, the asteroid belt's only dwarf planet, is about 950 km in diameter. The remaining bodies range down to the size of a dust particle. The asteroid material is so thinly distributed that numerous unmanned spacecraft have traversed it without incident. Nonetheless, collisions between large asteroids do occur, and these can form an asteroid family whose members have similar orbital characteristics and compositions. Individual asteroids within the asteroid belt are categorized by their spectra, with most falling into three basic groups: carbonaceous (C-type), silicate (S-type), and metal-rich (M-type).
The asteroid belt formed from the primordial solar nebula as a group of planetesimals, the smaller precursors of the planets, which in turn formed protoplanets. Between Mars and Jupiter, however, gravitational perturbations from Jupiter imbued the protoplanets with too much orbital energy for them to accrete into a planet. Collisions became too violent, and instead of fusing together, the planetesimals and most of the protoplanets shattered. As a result, 99.9% of the asteroid belt's original mass was lost in the first 100 million years of the Solar System's history. Some fragments can eventually find their way into the inner Solar System, leading to meteorite impacts with the inner planets. Asteroid orbits continue to be appreciablyperturbed whenever their period of revolution about the Sun forms an orbital resonance with Jupiter. At these orbital distances, a Kirkwood gap occurs as they are swept into other orbits.
Classes of small Solar System bodies in other regions include the centaurs, Kuiper belt and scattered disk objects, and Oort cloud comets.
On 22 January 2014, ESA scientists reported the detection, for the first definitive time, of water vapor on Ceres, the largest object in the asteroid belt. The detection was made by using the far-infrared abilities of the Herschel Space Observatory. The finding is unexpected because comets, not asteroids, are typically considered to "sprout jets and plumes". According to one of the scientists, "The lines are becoming more and more blurred between comets and asteroids."
The Asteroid Belt
Guiseppe Piazzi, Discoverer Of CERES
Giuseppe Piazzi, discoverer of Ceres, the largest object in the asteroid belt. For several decades after its discovery Ceres was known as a planet. after which it was reclassified as asteroid number 1. In 2006 it was recognized to be a dwarf planet.
Giuseppe Piazzi ( Born July 16, 1746 ) was an Italian Catholic priest of the Theatine order, mathematician, andastronomer. He was born in Ponte in Valtellina . He established an observatory at Palermo, now the Osservatorio Astronomico di Palermo – Giuseppe S. Vaiana. Perhaps his most famous discovery was the first asteroid, Ceres.
No documented account of Piazzi's scientific education is available in any of the biographies of the astronomer, even in the oldest ones. Piazzi certainly did some studies in Turin, quite likely attending Giovan Battista Beccaria's lessons. In the years 1768-1770 he was resident at the Theatines' Home in S. Andrea della Valle, Rome, while studying Mathematics under Francesco Jacquier.
Guiseppe Piazzi supervised the compilation of the Palermo Catalogue of stars, containing 7,646 star entries with unprecedented precision, including the star names "Garnet Star" fromHerschel, and the original Rotanev and Sualocin. The work on this catalogue was started in 1789, enabling Piazzi and collaborators to observe the sky methodically. The catalogue wasn't finished for first edition publication until 1803, and 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 in order 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. The star system 61 Cygni is sometimes still called variously Piazzi's Flying Star and Bessel's Star.
In July 1770, he took the chair of Mathematics at the University of Malta. In December 1773, he moved to Ravenna as "prefetto degli studenti" and lecturer in Philosophy and Mathematics at the Collegio dei Nobili, where he stayed until the beginning of 1779. After a short period spent in Cremona and in Rome, in March 1781 Piazzi moved to Palermo as lecturer in Mathematics at the University of Palermo (at the time known as "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, in order 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, 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.