ASTEROIDS, the name given to a large number of small planets, which revolve round the sun in orbits lying between those of Mars and Jupiter. They are all extremely small, their brightness seldom exceeding that of stars of the eighth magnitude; their paths, which cross and recross each other, extend over a belt about 250,000,000 miles in breadth; and the eccentricities of the orbits of many of them, and the inclinations of their planes to the plane of the ecliptic, are much greater than those of the larger planets. All the asteroids have been discovered during the present century. The first seen, Ceres, was discovered by Piazzi at Palermo on the first day of the century (Jan. 1, 1801), Pallas was seen in 1802, Juno in 1804, and Vesta in 1807. The next, Astrøea, was not discovered till 1845; three more were seen in 1847, and since that time the number has been increased every year, amounting at the end of 1874 to 140. (See Astronomy, p. 806.)