Johann Franz Encke

The Discovery of the Short Periodic Comets

Johann Franz Encke Portrait

Johann Franz Encke (1791-1865), Astronomer

At the 23rd of September 1791 Johann Franz Encke was born in Hamburg. He studied mathematics and astronomy from 1811 on at the Göttingen university with Carl Friedrich Gauß (1777-1855) as his teacher. 1812 he went to Kassel becoming himself teacher. In 1813 he fought during the liberation wars against Napoleon. After this, in 1814 he became an observer at the observatory on the Seeberg near Gotha.

At the end of 1818 Jean Lois Pons (1761-1831) discovered a weak comet, which had already been seen in 1786 by Pierre Mechain (1744-1804) and in 1795 by Caroline Herschel (1750-1848). January 1819 Encke calculated the orbit of this comet. Until then all the known comets only had an orbiting time of 70 years or more, were the aphelion is far beyond the Uranian orbit. The most famous comet of this family was the Halley comet with its orbiting time of ca. 76 years. The orbit of the comet discovered by Pons was a sensation, because this orbit had a round trip time of 3.3 years, therefore the aphelion had to be within the Jovian orbit. The perihelion of this comet is even within the Mercurian orbit.

Encke sent his calculations as a note to Gauß, Olbers, and Bessel. His former mathematics professor published this note and Encke became famous as the discoverer of the short periodic comets. The first object of this family was named after him and so it is one of the few comets not named after the discoverer, but named after the one who calculated the orbit.

2P/Encke in StarryNight

The Orbit of Comet 2P/Encke within the Solar System

After one orbit the comet was rediscovered and its orbital parameter calculated again. The results were indicating a slowing down of the orbiting time of 2-3 hours. Encke proposed an interstellar medium, an ether, with which he also wanted to resolve the known differences between theoretical and viewed orbiting times of the outer planets. However the slowing down of 2P/Encke was explained later by the thrust of the loss of cometary mass near Sun. Also later 2P/Encke was identified as the origin of the Taurids meteor stream.

In 1822 Encke became director of the observatory at Gotha, but then in 1825 he was called to Berlin by the Prussian king. Encke was ordered to plan a new observatory within the capital city. With the support by Alexander von Humboldt (1769-1859) at King Friedrich Wilhelm III., the observatory was built south of Berlin. The architect was Karl Friedrich Schinkel (1781-1841). The building had a basement which was divided into the observatory part and the residual house. The observatory had a rotatable 8 meter dome. The main observation instrument was a 9" Fraunhofer refractor. The building was inaugurated in 1835, and Encke became director of this new observatory.

In the Museum:

The Neue Sternwarte in Berlin, oil painting by Carl Daniel Freydanck (1811-1887), 1838

Subsequently Encke was involved in the discovery and orbital parameter determination of other short periodic comets and planetoids. But also the known planets were observed with the new instruments. In 1837 Encke discovered a (ca. 325 kilometer wide) gap within the A ring of Saturn, the so called Encke gap or Encke line. In 1838 his assistant and observer Johann Gottfried Galle (1812-1910) discovered the dark, inner C ring of Saturn at the time of the maxium ring opening. In 1846 Galle also discovered the last big planet of the solar system, Neptune, based on calculations by Urbain Leverrier (1811-1877). Galle became director of the observatory in Breslau in 1851.

In 1844 Encke was appointed as a university professor for astronomy in Berlin, but in 1863 he resigned from this job. He still remained director of the Berlin observatory until his death at the 26th of August 1865 in Spandau. His successor was Wilhelm Julius Foerster (1832-1921).

Sources:
Jaqueline Mitton: Penguin Dictionary of Astronomy in Redshift 2, Maris Multimedia 1995
Joachim Herrmann (ed.): Das große Lexikon der Astronomie, Orbis 1996
Fritz Krafft, Adolf Meyer-Abich (ed.): Große Naturwissenschaftler - Biographisches Lexikon, Fischer 1970

Page history:
created 1998-12-14 German version
modified 1998-12-18 translated
modified 2003-08-06 template changed
modified 2003-12-27 some correction

To the Sky over Berlin...To the astronomy links...-- jd --