Quick Facts
Born:
Sept. 23, 1791, Hamburg
Died:
Aug. 26, 1865, Spandau, Ger. (aged 73)

Johann Franz Encke (born Sept. 23, 1791, Hamburg—died Aug. 26, 1865, Spandau, Ger.) was a German astronomer who in 1819 established the period of the comet now known by his name (see Encke’s Comet).

Encke was educated at Hamburg and the University of Göttingen, where he worked under the direction of Carl Friedrich Gauss. In 1816 Encke became assistant at the Seeberg Observatory near Gotha, Ger., where he was made vice director in 1820 and director in 1822. In 1825 he was appointed professor of astronomy and director of the observatory of the University of Berlin. There he planned and supervised the construction of a new observatory, completed in 1835.

Besides the comet that bears his name, Encke is also known for his discovery of Encke’s Division, in the outermost ring of Saturn. From observations of the transits of Venus recorded in 1761 and 1769, he derived a value for the solar parallax (in effect, for the Sun’s distance from the Earth) that, at 8″.57, is close to the presently accepted figure. He also established methods for calculating the orbits of minor planets and orbits of double stars.

Michael Faraday (L) English physicist and chemist (electromagnetism) and John Frederic Daniell (R) British chemist and meteorologist who invented the Daniell cell.
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Also called:
Comet Encke

Encke’s Comet, faint comet having the shortest orbital period (about 3.3 years) of any known; it was also only the second comet (after Halley’s) to have its period established. The comet was first observed in 1786 by French astronomer Pierre Méchain. In 1819 German astronomer Johann Franz Encke deduced that sightings of apparently different comets in 1786, 1795, 1805, and 1818 were in fact appearances of the same comet and calculated its short orbital period. The comet was named in his honour, though usually comets are named after their discoverers. Encke also found that the comet’s orbital period was decreasing by about 2.5 hours every revolution and showed that this behaviour could not be explained by gravitational perturbations (slight changes in an orbit) caused by the planets. American astronomer Fred Whipple explained it in 1950 as the effect of jet forces produced by sublimation of water ice on the surface of the comet’s nucleus, in combination with the rotation of the nucleus.

This article was most recently revised and updated by Erik Gregersen.