OLBERS, WILHELM

born Oct. 11, 1758, Arbergen, near Bremen, Ger. died March 2, 1840, Bremen in full Heinrich Wilhelm Matthus Olbers German astronomer and physician who discovered the asteroids (minor planets) Pallas and Vesta as well as five comets. In 1779 Olbers devised a new method of calculating the orbits of comets. Two years later he opened his medical practice in Bremen, where he equipped the upper portion of his house for use as an observatory and devoted the greater part of each night to astronomy. He took a leading role in the search for a planet between Mars and Jupiter. In March 1802 he discovered Pallas and became convinced that asteroids are the broken-up remnants of a medium-sized planet that once orbited in the asteroid belt region. In 1811 Olbers formed the theory that the tail of a comet always points away from the Sun because of pressure from the Sun's radiation. (In the 20th century, radiation pressure from light was demonstrated in the laboratory.) Four years later he discovered the object now known as Olbers' Comet. In 1832 he predicted from observations of Biela's Comet that the Earth would pass through its tail. The prediction caused much tumult in Europe, but no catastrophic effects were noticed during the passage. Olbers also proposed what is known as Olbers' paradox.