Johann Franz Encke | |
|---|---|
 Johann Franz Encke | |
| Born | (1791-09-23)23 September 1791 |
| Died | 26 August 1865(1865-08-26) (aged 73) |
| Alma mater | University of Göttingen |
| Known for | 12P/Pons-Brookscomet |
| Awards | Cotta prize(1817) Royal Medal(1828) Gold Medal of the Royal Astronomical Society(1824, 1830) |
| Scientific career | |
| Fields | Astronomy |
| Institutions | University of Berlin |
| Academic advisors | Carl Friedrich Gauss |
| Doctoral students | Johann Gottfried Galle Leopold Kronecker Demetrios Kokkidis |
Johann Franz Encke (German pronunciation:[ˈjoːhanˈfʁantsˈɛŋkə]; 23 September 1791 – 26 August 1865) was a Germanastronomer. Among his activities, he worked on the calculation of the periods of comets and asteroids, measured the distance from the Earth to the Sun, and made observations of the planet Saturn.
Encke was born inHamburg, where his father was the Pastor atSt. James' Church, Hamburg. He was the youngest of eight children, and at the time his father died, when he was four years old, the family was in straitened circumstances. Thanks to the financial assistance of a teacher, he was able to be educated at theGelehrtenschule des Johanneums. He studiedmathematics andastronomy from 1811 at theUniversity of Göttingen underCarl Friedrich Gauss, but he enlisted in theHanseatic Legion for the campaign of 1813–1814, serving as a sergeant in the artillery of thePrussian army, in Holstein and Mecklenburg. In 1814 he resumed his studies at the University, but afterNapoleon's escape from Elba he returned to the military, serving until 1815 by which time he had become a lieutenant.[1]
Having returned to Göttingen in 1816, he was at once appointed byBernhardt von Lindenau as his assistant in theobservatory of Seeberg nearGotha (he had become acquainted with von Lindenau during his military service). There he completed his investigation of thecomet of 1680, for which theCotta prize was awarded to him in 1817 by judges Gauss andOlbers. He correctly assigned a period of 71 years to the comet of 1812, now known as12P/Pons-Brooks.[1]
Following a suggestion byJean-Louis Pons, who suspected one of the three comets discovered in 1818 to be the same one already discovered by him in 1805, Encke began to calculate theorbital elements of this comet. At this time, all the known comets had anorbital period of seventy years and more, with anaphelion far beyond the orbit ofUranus. The most famous comet of this family wasComet Halley with its period of seventy-six years. Therefore the orbit of the comet discovered by Pons was a sensation, because his orbit was found to have a period of 3.3 years, so that the aphelion had to be within the orbit ofJupiter. Encke predicted its return for 1822; this return was observable only from the southern hemisphere and was seen byCarl Ludwig Christian Rümker in Australia. The comet was also identified with the one seen byPierre Méchain in 1786 and byCaroline Herschel in 1795.
Encke sent his calculations as a note to Gauss, Olbers, andBessel. 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, theEncke comet, was named after him and so it is one of the few comets not named after the discoverer, but after the one who calculated the orbit. Later this comet was identified as the origin of theTauridsmeteor showers.
The importance of the predicted return based on the calculation by Encke was rewarded by theRoyal Astronomical Society in London by presenting theirGold Medal to him in 1824. In this year Encke marriedAmalie Becker (1787–1879), daughter of author, bookseller and publisherRudolph Zacharias Becker, the publisher of works from the Seeberg Observatory. They had three sons and two daughters. In 1825 he was elected aFellow of the Royal Society.[2]
Eight masterly treatises on the comet's movements were published by him in theBerliner Abhandlungen (1829–1859). From a fresh discussion of thetransits of Venus in 1761 and 1769 he deduced a solarparallax of 8.57arcsecond. This and the corresponding distance to the sun were long accepted as authoritative.[1] His results were published in two separate tracts, entitledDie Entfernung der Sonne (The distance to the Sun, 1822–1824).
In 1822 he became director of theSeeberg observatory, and in 1825 was promoted to a corresponding position atBerlin, wherea new observatory, built under his superintendence and with the support ofAlexander von Humboldt and KingFrederick William III of Prussia, was inaugurated in 1835.[1] Mostly on the recommendation of Bessel, Encke became director of the new observatory and secretary of theAcademy of Sciences.He directed the preparation of the star maps of the Academy (1830–1859); beginning in 1830, he edited and greatly improved theAstronomisches Jahrbuch; and he issued four volumes of theAstronomische Beobachtungen auf der Sternwarte zu Berlin (Observations of the Berlin observatory, 1840–1857).[1] Thereafter Encke was involved in the discovery and orbital parameter determination of other short periodic comets andasteroids.
In 1837, Encke described a broad variation in the brightness of theA Ring ofSaturn. TheEncke Gap was later named in honour of his observations of Saturn's rings.
In 1844, Encke became professor of astronomy at theUniversity of Berlin. Much labour was bestowed by him upon facilitating the computation of the movements of the asteroids. With this end in view he expounded to the Berlin Academy in 1849 a mode of determining anelliptic orbit from three observations, and communicated to that body in 1851 a new method of calculating planetary perturbations by means of rectangular coordinates (republished in W. Ostwald'sKlassiker der exacten Wissenschaften, No. 141, 1903).[1]
Encke visited England in 1840. He was elected a foreign member of theRoyal Swedish Academy of Sciences in 1836, a member to theAmerican Philosophical Society in 1839,[3] and a Foreign Honorary Member of theAmerican Academy of Arts and Sciences in 1849.[4] Incipient brain-disease compelled him to withdraw from official life in November 1863.[1] He still was director of the Berlin observatory until his death on 26 August 1865 inSpandau. His successor wasWilhelm Julius Foerster.
He contributed extensively to the periodical literature of astronomy.[1]
Encke's grave is preserved at a cemetery in theKreuzberg section of Berlin, theFriedhof II der Jerusalems- und Neuen Kirchengemeinde (Cemetery No. II of the congregations ofJerusalem's Church andNew Church) (entrance: opposite to 58–60, Zossener Str.; 61, Baruther Str. only for vehicles of the cemetery). His grave is close to that of the mathematicianCarl Gustav Jacob Jacobi.
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One or more of the preceding sentences incorporates text from a publication now in thepublic domain: Clerke, Agnes Mary (1911). "Encke, Johann Franz". InChisholm, Hugh (ed.).Encyclopædia Britannica. Vol. 9 (11th ed.). Cambridge University Press. p. 369.
