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| Alternative names | Copenhagen University Observatory |
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| Observatory code | 035 |
| Location | Copenhagen Municipality,Capital Region of Denmark, Denmark |
| Coordinates | 55°41′13″N12°34′33″E / 55.686883°N 12.575919°E /55.686883; 12.575919 |
  Location of Østervold Observatory | |
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Østervold Observatory (orCopenhagen University Observatory;Danish:Københavns Universitet Astronomisk Observatorium) is a formerastronomicalobservatory (IAU code 035) inCopenhagen, Denmark owned and operated by theUniversity of Copenhagen (Københavns Universitet). It opened in 1861 as a replacement for the university's old observatory atRundetårn.
The Østervold Observatory building house theInstitute for Science Didactics of the University of Copenhagen.
The first astronomical observatory operated by the University of Copenhagen wasRundetårn. It had been inaugurated in 1642 as a replacement forTycho Brahe'sStjerneborg, but during the early 19th century had become outdated as astronomical instruments grew bigger and bigger while the tower could not be expanded. In the same time,light pollution from the surrounding city as well as vibrations caused by the still increasing traffic in the streets below had made the observations inaccurate.
In 1861 the observatory was moved toØstervold, where a new observatory was constructed on the oldbastioned fortifications of the city, which had become outdated and were being abandoned. The well-known Russian-German astronomer,Heinrich Louis d'Arrest, who had been appointed professor in astronomy at the university in 1857, was chosen to plan the new observatory. He used the observatory for his study ofnebulas, in 1867 publishing anastronomical catalogue of 1,942 nebulas with 4,900 positions. He also did significant work inspectroscopy, and discovered, for the first time, the differences in the evolutionary state and spatial distribution of stars. While d'Arrest used the main telescope, observer H. C. F. C. Schjellerup used the Meridian circle for creating one of the most comprehensive astronomical catalogues of the time of stars of the 8th-9thmagnitude: 10,000 positions on 259 observation nights.[1]
The next director of the Østervold Observatory wasThorvald N. Thiele, a skilful mathematician who developed a new method of determining the orbit ofBinary stars. He founded the tradition for numerical computational mathematics, which has lasted up to modern times.[2]
In 1907,Elis Strömgren was appointed professor and director of the observatory, and under his direction the computational work continued.
DuringWorld War I, theCentral Bureau for Astronomical Telegrams, founded byAstronomische Gesellschaft in 1882, was moved fromKiel, Germany, to the Østervold Observatory.[3] It remained located in Copenhagen until 1965, when it was moved to theSmithsonian Astrophysical Observatory,Cambridge, United States.[1]
In 1940 Ellis Strömgren was succeeded by his sonBengt Strömgren, who made the pioneering discovery thathydrogen is the most abundant element in thestellar interior. He was also the first to make the correct interpretation of theHertzsprung–Russell diagram (the relation between the total energy output from a star and its surface temperature was independently found by the Danish chemist and astronomerEjnar Hertzsprung and the American astronomerHenry Norris Russell). Around 1950, he developed theuvbyß photoelectric system, which is still in use today.[2]
In the 1950s, the Østervold Observatory was replaced by theBrorfelde Observatory located near the town ofHolbæk, which was provided with a very fine meridian circle and aSchmidt telescope with a camera that used photographic film. It houses a 300 doublereflector with a focal depth of 4.9m.
The Østervold Observatory is a south-facing, three-winged building, designed byChristian Hansen. The central wing is topped by adome. containing the main instrument. The side wings contained residences for the director, the observer as well as assistants. To secure the best possible foundation of the instruments, the foundation of the building rests on the original, true ground surface, penetrating the entire depth of the ramparts on which the building stands. This took 1/3 of the bricks used for the entire complex.
The Østervold Observatory building is no longer used for astronomy, but it was often used among ornithologists. The buildings house the Institute for Science Didactics University of Copenhagen.[4]
The original main instrument of the observatory, housed in the dome, was a 280 mm refractor with a focal distance of 4.9 m. In 1895, this telescope was replaced by a 360 mm refractor with a focal length of 4.9 m and a 200 mm photographic lens with a focal length of 4.8 m. The purchase of the double refractor enabled the observatory to participate in photographic observations without having to give up visual observations. This double refractor is still found in the dome of the Østervold Observatory, while the 1861 refractor is displayed at the Steno Museum inÅrhus.[1]c
1862-1875:Heinrich Louis d'Arrest
1875-1907:Thorvald N. Thiele
1907-1940:Elis Strömgren
1940–1951.Bengt Strömgren
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