Johann Franz Encke

{{Short description|German astronomer (1791–1865)}} {{distinguish|text=[[Karl Ludwig Hencke]], another German astronomer}} {{EngvarB|date=July 2017}} {{Use dmy dates|date=July 2017}} {{Infobox scientist |name = Johann Franz Encke |image =Johann Franz Encke.jpg |image_size = 250px |caption = Johann Franz Encke |birth_date = {{birth date|df=yes|1791|9|23}} |birth_place = [[Hamburg]], [[Holy Roman Empire]] |death_date = {{death date and age|df=yes|1865|8|26|1791|9|23}} |death_place = [[Spandau]] (now part of [[Berlin]]), [[Province of Brandenburg]] |residence = |citizenship = |ethnicity = |field = [[Astronomy]] |work_institutions = [[Humboldt University of Berlin|University of Berlin]] |alma_mater = [[University of Göttingen]] |doctoral_advisor =  |academic_advisors = [[Carl Friedrich Gauss]] |doctoral_students = [[Johann Gottfried Galle]]<br>[[Leopold Kronecker]]<br>[[Demetrios Kokkidis]] |known_for = [[12P/Pons-Brooks]] [[comet]] |influences = |influenced = |prizes = [[Cotta prize]] {{small|(1817)}}<br>[[Royal Medal]] {{small|(1828)}}<br>[[Gold Medal of the Royal Astronomical Society]] {{small|(1824, 1830)}} |religion = |footnotes = |signature = }}

'''Johann Franz Encke''' ({{IPA|de|ˈjoːhan ˈfʁants ˈɛŋkə}}; 23 September 1791{{snd}}26 August 1865) was a German [[astronomer]]. 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.

==Biography== Encke was born in [[Hamburg]], where his father was the Pastor at [[St. 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 the [[Gelehrtenschule des Johanneums]]. He studied [[mathematics]] and [[astronomy]] from 1811 at the [[University of Göttingen]] under [[Carl Friedrich Gauss]], but he enlisted in the [[Hanseatic Legion]] for the campaign of 1813–1814, serving as a sergeant in the artillery of the [[Prussian army]], in Holstein and Mecklenburg. In 1814 he resumed his studies at the University, but after [[Napoleon]]'s escape from Elba he returned to the military, serving until 1815 by which time he had become a lieutenant.<ref name="EB1911">{{EB1911|inline=y|wstitle=Encke, Johann Franz|volume=9|page=369|first=Agnes Mary|last=Clerke|authorlink=Agnes Mary Clerke}}</ref>

Having returned to Göttingen in 1816, he was at once appointed by [[Bernhardt von Lindenau]] as his assistant in the [[Gotha Observatory|observatory of Seeberg]] near [[Gotha (town)|Gotha]] (he had become acquainted with von Lindenau during his military service). There he completed his investigation of the [[Great comet of 1680|comet of 1680]], for which the [[Cotta prize]] was awarded to him in 1817 by judges Gauss and [[Heinrich Wilhelm Olbers|Olbers]]. He correctly assigned a period of 71 years to the comet of 1812, now known as ''[[12P/Pons-Brooks]]''.<ref name="EB1911"/>

Following a suggestion by [[Jean-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 the [[orbital elements]] of this comet. At this time, all the known comets had an [[orbital period]] of seventy years and more, with an [[aphelion]] far beyond the orbit of [[Uranus]]. The most famous comet of this family was [[Comet 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 of [[Jupiter]]. Encke predicted its return for 1822; this return was observable only from the southern hemisphere and was seen by [[Carl Ludwig Christian Rümker]] in Australia. The comet was also identified with the one seen by [[Pierre Méchain]] in 1786 and by [[Caroline Herschel]] in 1795.

Encke sent his calculations as a note to Gauss, Olbers, and [[Friedrich Bessel|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, the [[Encke 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 the [[Taurids]] [[meteor shower]]s.

The importance of the predicted return based on the calculation by Encke was rewarded by the [[Royal Astronomical Society]] in London by presenting their [[Gold Medal of the Royal Astronomical Society|Gold Medal]] to him in 1824. In this year Encke married [[Amalie Becker]] (1787–1879), daughter of author, bookseller and publisher [[Rudolph Zacharias Becker]], the publisher of works from the Seeberg Observatory. They had three sons and two daughters. In 1825 he was elected a [[Fellow of the Royal Society]].<ref>{{cite web|url= http://www2.royalsociety.org/DServe/dserve.exe?dsqIni=Dserve.ini&dsqApp=Archive&dsqCmd=Show.tcl&dsqDb=Persons&dsqPos=0&dsqSearch=%28Surname%3D%27encke%27%29|title= Library and Archive Catalogue|publisher= [[Royal Society]]|access-date= 30 November 2010}}{{dead link|date=January 2018 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

Eight masterly treatises on the comet's movements were published by him in the ''Berliner Abhandlungen'' (1829–1859). From a fresh discussion of the [[transit of Venus|transits of Venus]] in 1761 and 1769 he deduced a solar [[parallax]] of 8.57 [[arcsecond]]. This and the corresponding distance to the sun were long accepted as authoritative.<ref name="EB1911"/> His results were published in two separate tracts, entitled ''Die Entfernung der Sonne'' (The distance to the Sun, 1822–1824).

In 1822 he became director of the [[Seeberg]] observatory, and in 1825 was promoted to a corresponding position at [[Berlin]], where [[Berlin Observatory|a new observatory]], built under his superintendence and with the support of [[Alexander von Humboldt]] and King [[Frederick William III of Prussia]], was inaugurated in 1835.<ref name="EB1911"/> Mostly on the recommendation of Bessel, Encke became director of the new observatory and secretary of the [[Prussian Academy of Sciences|Academy of Sciences]]. He directed the preparation of the star maps of the Academy (1830–1859); beginning in 1830, he edited and greatly improved the ''Astronomisches Jahrbuch''; and he issued four volumes of the ''Astronomische Beobachtungen auf der Sternwarte zu Berlin'' (Observations of the Berlin observatory, 1840–1857).<ref name="EB1911"/> Thereafter Encke was involved in the discovery and orbital parameter determination of other short periodic comets and [[asteroids]].

In 1837, Encke described a broad variation in the brightness of the [[Rings of Saturn#A Ring|A Ring]] of [[Saturn]]. The [[Rings of Saturn#Encke Gap|Encke Gap]] was later named in honour of his observations of Saturn's rings.

In 1844, Encke became professor of astronomy at the [[Humboldt University of Berlin|University 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 an [[elliptic 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's ''Klassiker der exacten Wissenschaften'', No. 141, 1903).<ref name="EB1911"/>

Encke visited England in 1840. He was elected a foreign member of the [[Royal Swedish Academy of Sciences]] in 1836, a member to the [[American Philosophical Society]] in 1839,<ref>{{Cite web|title=APS Member History|url=https://search.amphilsoc.org/memhist/search?creator=&title=&subject=&subdiv=&mem=&year=1839&year-max=1839&dead=&keyword=&smode=advanced|access-date=2021-04-09|website=search.amphilsoc.org}}</ref> and a Foreign Honorary Member of the [[American Academy of Arts and Sciences]] in 1849.<ref name=AAAS>{{cite web|title=Book of Members, 1780–2010: Chapter E|url=http://www.amacad.org/publications/BookofMembers/ChapterE.pdf|publisher=[[American Academy of Arts and Sciences]]|access-date=15 September 2016}}</ref> Incipient brain-disease compelled him to withdraw from official life in November 1863.<ref name="EB1911"/> He still was director of the Berlin observatory until his death on 26 August 1865 in [[Spandau]]. His successor was [[Wilhelm Julius Foerster]].

He contributed extensively to the periodical literature of astronomy.<ref name="EB1911"/>

Encke's grave is preserved at a cemetery in the [[Kreuzberg]] section of Berlin, the ''Friedhof II der Jerusalems- und Neuen Kirchengemeinde'' (Cemetery No. II of the congregations of [[Jerusalem's Church]] and [[Deutscher Dom|New 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 mathematician [[Carl Gustav Jacob Jacobi]].

==Honors== *Twice, in 1824 and 1830, the recipient of the [[Gold Medal of the Royal Astronomical Society]].<ref name="EB1911"/> *The crater [[Encke (crater)|Encke]] on the [[Moon]] is named after him. *[[Asteroid]] [[9134 Encke]] is named in his honour. *The [[Rings of Saturn#Encke Gap|Encke gap]] of Saturn's rings is named after him. *[[Comet Encke]] is named after him for his calculation of its orbit.

==Notes== {{More footnotes|date=October 2019}} {{reflist|30em}} {{Commons}}

==References== *{{Cite NIE|wstitle=Encke, Johann Franz|year=1905}}

==External links== * [http://adsabs.harvard.edu//full/seri/MNRAS/0026//0000129.000.html Obituary of "John Francis Encke"]

{{DEFAULTSORT:Encke, Johann Franz}} [[Category:1791 births]] [[Category:1865 deaths]] [[Category:Scientists from Hamburg]] [[Category:19th-century German astronomers]] [[Category:Prussian Army personnel of the Napoleonic Wars]] [[Category:Recipients of the Gold Medal of the Royal Astronomical Society]] [[Category:University of Göttingen alumni]] [[Category:Academic staff of the Humboldt University of Berlin]] [[Category:Royal Medal winners]] [[Category:Members of the Royal Swedish Academy of Sciences]] [[Category:Fellows of the American Academy of Arts and Sciences]] [[Category:Honorary members of the Saint Petersburg Academy of Sciences]] [[Category:Recipients of the Pour le Mérite (civil class)]] [[Category:People educated at the Gelehrtenschule des Johanneums]] [[Category:Recipients of the Lalande Prize]] [[Category:International members of the American Philosophical Society]] [[Category:German fellows of the Royal Society]]