Ceres

Ceres , in astronomy, a dwarf planet, the first asteroid to be discovered. It was found on Jan. 1, 1801, by G. Piazzi . He took three distinct observations; on the basis of these the mathematician Gauss calculated Ceres' orbit with such accuracy that it was found one year later within 0.5° of the predicted position. Ceres is the largest and most massive of the asteroids; it has a diameter of c.590 mi (949 km) and a mass 1/100,000 that of the earth. Its orbit has a semimajor axis of 2.78 astronomical units and a period of 1,681 days. From its discovery until the 1850s, when many additional asteroids began to be identified, Ceres was regarded by many astronomers as a planet. In 2006 the reconsideration by astronomers of Pluto 's status as a planet also led to the reclassification of Ceres as a dwarf planet.

Ceres The first asteroid to be discovered, by G.Piazzi on 1801January1, and hence given the number 1. Ceres is by far the largest asteroid, diameter 940 km, mass 9 × 10²⁰ kg (about 1% the mass of the Moon) and mean density c.2.0 g/cm³. Its rotation period is 9.075 hours. Ceres contains roughly one-third the mass of the entire asteroid belt. It is a member of the new class of dwarf planets, along with Eris and Pluto. Its mean magnitude at opposition is 7.4; only Vesta can ever become brighter. Its orbit has a semimajor axis of 2.767 AU, period 4.60 years, perihelion 2.55 AU, aphelion 2.98 AU, and inclination 10°.6. Ceres is of G class, with a reflectance spectrum that implies a composition resembling the carbonaceous chondrite meteorites. Ceres is the largest member of a small family of asteroids with a mean distance of 2.76–2.80 AU from the Sun and orbital inclinations of 9–11°. Other Ceres family members include (39) Laetitia, (264) Libussa, (374) Burgundia (all S-class), and (446) Aeternitas (A-class).

Ceres The largest solar system asteroid (No. 1), diameter 974 km, approximate mass 10²¹ kg; rotation period 9.078 hours; orbital period 4.6 years. It was discovered in 1801 by G. Piazzi. It accounts for almost half the total estimated mass of all the asteroids.