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(sīr“ēz)
, in astronomy, 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.630 mi (1000 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.
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