Heinrich Wilhelm Matthans Olbers, a German astronomer, born at Arbergen, near Bremen, Oct. 11, 1758, died in Bremen, March 2, 1840. He was a practising physician, and made his observations from an upper chamber of his dwelling in Bremen, with an ordinary hand telescope. He applied himself especially to the study of comets, and in 1779 discovered a method of calculating their orbits which was greatly superior to those previously in use. He computed the orbits of the comets of 1781, 1795, 1798, 1799, 1802, and of the great one of 1811. He also made investigations respecting the existence of the small planets whose orbits lie between Mars and Jupiter. Kepler had suggested that a planetary body might occupy this space; and with a view of verifying this suggestion, an association of 24 astronomers, including Olbers, divided up the zodiac among themselves for independent scrutiny. On Jan. 1,1801, the small planet Ceres was discovered by Piazzi of Palermo, who was not a member of the association; and on March 28, 1802, Olbers discovered in the northern part of the constellation Virgo the planet Pallas. This led Olbers to conjecture that they were fragments of a larger planet once existing there, and that probably other portions might be found moving in nearly the same orbit; but he said he advanced the hypothesis merely to serve as a guide in making observations. (See Asteeoids.) He accordingly explored carefully, every month, the two opposite regions of the heavens in which the orbits of the new planets intersected, and where he supposed the fragments of the shattered planet must pass.

In September, 1804, M. Harding of Bremen accidentally discovered a third planet, Juno. Olbers continued his search with renewed ardor, and on March 29, 1807, discovered a fourth, Vesta. In March, 1815, he discovered near Perseus a comet having no visible nucleus, and in 1828 published a dissertation on the possibility of a collision between a comet and the earth. His library, which contained perhaps the most extensive collection in existence of works in regard to comets, was purchased by the Russian government for the observatory of Pulkova.