Ole Rømer

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Ole Rømer
Ole Rømer (Coning painting).jpg
Ole Rømer, portrait by Jacob Coning from c. 1700
Born (1644-09-25)25 September 1644
Died 19 September 1710(1710-09-19) (aged 65)
Nationality Danish
Fields Astronomy
Known for speed of light

Ole Christensen Rømer (Danish pronunciation: [o(ː)lə ˈʁœːˀmɐ]; 25 September 1644 – 19 September 1710) was a Danish astronomer who in 1676 made the first quantitative measurements of the speed of light. In scientific literature alternative spellings such as "Roemer", "Römer", or "Romer" are common.

General biography[edit]

Rundetårn, or round tower, in Copenhagen, on top of which the university had its observatory from the mid 17th century until the mid 19th century, when it was moved to new premises. The current observatory there was built in the 20th century to serve amateurs.

Rømer was born on 25 September 1644 in Århus to a merchant and skipper, Christen Pedersen (died 1663), and Anna Olufsdatter Storm (c. 1610-1690), daughter of a well-to-do alderman.[1] Since 1642, Christen Pedersen had taken to using the name Rømer, which means that he was from the Danish island of Rømø, to distinguish himself from a couple of other people named Christen Pedersen.[2] There are few records of Ole Rømer before 1662, when he graduated from the old Aarhus Katedralskole (the Cathedral school of Aarhus),[3][4] moved to Copenhagen and matriculated at the University of Copenhagen. His mentor at the University was Rasmus Bartholin, who published his discovery of the double refraction of a light ray by Iceland spar (calcite) in 1668, while Rømer was living in his home. Rømer was given every opportunity to learn mathematics and astronomy using Tycho Brahe's astronomical observations, as Bartholin had been given the task of preparing them for publication.[5]

Rømer was employed by the French government: Louis XIV made him tutor for the Dauphin, and he also took part in the construction of the magnificent fountains at Versailles.

In 1681, Rømer returned to Denmark and was appointed professor of astronomy at the University of Copenhagen, and the same year he married Anne Marie Bartholin, the daughter of Rasmus Bartholin. He was active also as an observer, both at the University Observatory at Rundetårn and in his home, using improved instruments of his own construction. Unfortunately, his observations have not survived: they were lost in the great Copenhagen Fire of 1728. However, a former assistant (and later an astronomer in his own right), Peder Horrebow, loyally described and wrote about Rømer's observations.

In Rømer's position as royal mathematician, he introduced the first national system for weights and measures in Denmark on 1 May 1683.[6][7] Initially based on the Rhine foot, a more accurate national standard was adopted in 1698.[8] Later measurements of the standards fabricated for length and volume show an excellent degree of accuracy. His goal was to achieve a definition based on astronomical constants, using a pendulum. This would happen after his death, practicalities making it too inaccurate at the time. Notable is also his definition of the new Danish mile of 24,000 Danish feet (circa 7,532 m).[9]

In 1700, Rømer persuaded the king to introduce the Gregorian calendar in Denmark-Norway — something Tycho Brahe had argued for in vain a hundred years earlier.[10]

Ole Rømer at work

Rømer developed one of the first temperature scales while convalescing from a broken leg.[11] Fahrenheit visited him in 1708 and improved on the Rømer scale, the result being the familiar Fahrenheit temperature scale still in use today in a few countries.[12][13][14]

Rømer also established navigation schools in several Danish cities.[15]

In 1705, Rømer was made the second Chief of the Copenhagen Police, a position he kept until his death in 1710.[16] As one of his first acts, he fired the entire force, being convinced that the morale was alarmingly low. He was the inventor of the first street lights (oil lamps) in Copenhagen, and worked hard to try to control the beggars, poor people, unemployed, and prostitutes of Copenhagen.[17][18]

In Copenhagen, Rømer made rules for building new houses, got the city's water supply and sewers back in order, ensured that the city's fire department got new and better equipment, and was the moving force behind the planning and making of new pavement in the streets and on the city squares.[19][20][21]

Roemer died at the age of 65 in 1710.[22]

Rømer and the speed of light[edit]

The determination of longitude is a significant practical problem in cartography and navigation. Philip III of Spain offered a prize for a method to determine the longitude of a ship out of sight of land, and Galileo proposed a method of establishing the time of day, and thus longitude, based on the times of the eclipses of the moons of Jupiter, in essence using the Jovian system as a cosmic clock; this method was not significantly improved until accurate mechanical clocks were developed in the eighteenth century. Galileo proposed this method to the Spanish crown (1616–1617) but it proved to be impractical, because of the inaccuracies of Galileo's timetables and the difficulty of observing the eclipses on a ship. However, with refinements the method could be made to work on land.

After studies in Copenhagen, Rømer joined the observatory of Uraniborg on the island of Hven, near Copenhagen, in 1671. Over a period of several months, Jean Picard and Rømer observed about 140 eclipses of Jupiter's moon Io, while in Paris Giovanni Domenico Cassini observed the same eclipses. By comparing the times of the eclipses, the difference in longitude of Paris to Uranienborg was calculated.

Cassini had observed the moons of Jupiter between 1666 and 1668, and discovered discrepancies in his measurements that, at first, he attributed to light having a finite speed. In 1672 Rømer went to Paris and continued observing the satellites of Jupiter as Cassini's assistant. Rømer added his own observations to Cassini's and observed that times between eclipses (particularly those of Io) got shorter as Earth approached Jupiter, and longer as Earth moved farther away. Cassini made an announcement to the Academy of Sciences on 22 August 1676:

This second inequality appears to be due to light taking some time to reach us from the satellite; light seems to take about ten to eleven minutes [to cross] a distance equal to the half-diameter of the terrestrial orbit.[23]

Illustration from the 1676 article on Rømer's measurement of the speed of light. Rømer compared the duration of Io's orbits as Earth moved towards Jupiter (F to G) and as Earth moved away from Jupiter (L to K).

Oddly, Cassini seems to have abandoned this reasoning, which Rømer adopted and set about buttressing in an irrefutable manner, using a selected number of observations performed by Picard and himself between 1671 and 1677. Rømer presented his results to the French Academy of Sciences, and it was summarised soon after by an anonymous reporter in a short paper, Démonstration touchant le mouvement de la lumière trouvé par M. Roemer de l'Académie des sciences, published 7 December 1676 in the Journal des sçavans. Unfortunately the paper bears the stamp of the reporter failing to understand Rømer's presentation, and as the reporter resorted to cryptic phrasings to hide his lack of understanding, he obfuscated Rømer's reasoning in the process. Unfortunately Rømer himself never published his results.[24]

Assume the Earth is in L, at the second quadrature with Jupiter (i.e. ALB is 90°), and Io emerges from D. After several orbits of Io, at 42.5 hours per orbit, the Earth is in K. Rømer reasoned that if light is not propagated instantaneously, the additional time it takes to reach K, that he reckoned about 3½ minutes, would explain the observed delay. Rømer observed immersions in C from the symmetric positions F and G, to avoid confusing eclipses (Io shadowed by Jupiter from C to D) and occultations (Io hidden behind Jupiter at various angles). In the table below, his observations in 1676, including the one on August 7, believed to be in opposition H,[25] and the one observed at Paris Observatory to be 10 minutes late, on November 9.[26]

The eclipses of Io recorded by Rømer in 1676
Time is normalized (hours since midnight rather than since noon); values on even rows are calculated from the original data.
Month Day Time Tide orbits average (hours)
June 13 2:49:42 C
2,750,789s 18 42.45
May 13 22:56:11 C
4,747,719s 31 42.54
Aug 7 21:44:50 D
612,065s 4 42.50
Aug 14 23:45:55 D
764,718s 5 42.48
Aug 23 20:11:13 D
6,906,272s 45 42.63
Nov 9 17:35:45 D

By trial and error, during eight years of observations Rømer worked out how to account for the retardation of light when reckoning the ephemeris of Io. He calculated the delay as a proportion of the angle corresponding to a given Earth's position with respect to Jupiter, Δt = 22·(α180°)[minutes]. When the angle α is 180° the delay becomes 22 minutes, which may be interpreted as the time necessary for the light to cross a distance equal to the diameter of the Earth's orbit, H to E.[26] (Actually, Jupiter is not visible from the conjunction point E.) That interpretation makes it possible to calculate the strict result of Rømer's observations: The ratio of the speed of light to the speed with which Earth orbits the sun, which is the ratio of the duration of a year divided by pi as compared to the 22 minutes

365·24·60π·22 ≈ 7,600.

In comparison the modern value is circa 299,792 km s−129.8 km s−1 ≈ 10,100.[27]

Rømer neither calculated this ratio, nor did he give a value for the speed of light. However, many others calculated a speed from his data, the first being Christiaan Huygens; after corresponding with Rømer and eliciting more data, Huygens deduced that light travelled 16 23 Earth diameters per second.[28]

Rømer's view that the velocity of light was finite was not fully accepted until measurements of the so-called aberration of light were made by James Bradley in 1727.

In 1809, again making use of observations of Io, but this time with the benefit of more than a century of increasingly precise observations, the astronomer Jean Baptiste Joseph Delambre reported the time for light to travel from the Sun to the Earth as 8 minutes and 12 seconds. Depending on the value assumed for the astronomical unit, this yields the speed of light as just a little more than 300,000 kilometres per second. The modern value is 8 minutes and 19 seconds, and a speed of 299,792.458 km/s.

A plaque at the Observatory of Paris, where the Danish astronomer happened to be working, commemorates what was, in effect, the first measurement of a universal quantity made on this planet.


In addition to inventing the first street lights in Copenhagen,[29][30] Rømer also invented the meridian circle,[31][32][33] the altazimuth,[34][35] and the Passage Instrument.[36][37]

Ole Romer Medal[edit]

The Ole Romer Medal (da) is given annually by the Danish Natural Science Research Council for outstanding research.[38]

The Ole Rømer Museum[edit]

The Ole Rømer Museum is located in the municipality of Høje-Taastrup, Denmark,[39] at the excavated site of Rømer's observatory Observatorium Tusculanum (da) at Vridsløsemagle.[40][41][42] The observatory opened in 1704, and operated until about 1716, when the remaining instruments were moved to Rundetårn in Copenhagen.[43] There is a large collection of ancient and more recent astronomical instruments on display at the museum.[44] The museum opened in 1979, and has since 2002 been a part of the museum Kroppedal at the same location.[45][46][47]


In Denmark, Ole Rømer has been honoured in various ways through the ages. He has been portrayed on bank notes,[48] the eponymous Ole Rømer's Hill (da) is named after him,[49] as are streets in both Aarhus and Copenhagen (Ole Rømers Gade and Rømersgade (da) respectively).[50][51] Aarhus University's astronomical observatory is named The Ole Rømer Observatory (Ole Rømer Observatoriet (da)) in his honour, and a Danish satellite project to measure the age, temperature, physical and chemical conditions of selected stars, was named The Rømer Satellite (da). The satellite project stranded in 2002 and was never realised though.[52][53]

The Römer crater on the Moon is named after him.[54]

Popular culture[edit]

Ole Rømer features in the game Empire: Total War as a gentleman under Denmark.

In the 1960s, the comic-book superhero The Flash on a number of occasions would measure his velocity in "Roemers" [sic], in honour of Ole Rømer's "discovery" of the speed of light.[55][better source needed]

General references[edit]

Notes and references[edit]

  1. ^ Niels Dalgaard (1996). Dage med Madsen, eller, Livet i Århus: om sammenhænge i Svend Åge Madsens forfatterskab (in Danish). Museum Tusculanum Press. pp. 169–. ISBN 978-87-7289-409-6. ... skipper og handelsmand i Århus, gift med Anne Olufsdatter Storm (død 1690) og far til astronomen Ole Rømer (1644-1710). 
  2. ^ Friedrichsen, Per; Tortzen, Chr. Gorm (2001). Ole Rømer – Korrespondance og afhandlinger samt et udvalg af dokumenter (in Danish). Copenhagen: C. A. Reitzels Forlag. p. 16. ISBN 87-7876-258-8. 
  3. ^ Bogvennen (in Danish) 1–9. Fischers forlag. 1971. pp. 66–. Denne antagelse tiltrænger en nærmere redegørelse: Ole Rømer udgik som student fra Aarhus Katedralskole i 1662. Ole Rømer Skolens rektor på den tid var Niels Nielsen Krog, om hvem samtidige kilder oplyser, at »hans studium ... 
  4. ^ Olaf Lind; Poul Ib Henriksen (2003). Arkitektur Fortaellinger/Building of Aarhus University (in Danish). Aarhus Universitetsforlag. pp. 21–. ISBN 978-87-7288-972-6. Ole Rømer tog i øvrigt studentereksamen fra Latinskolen i Ãrhus (Katedralskolen) i 1662. 
  5. ^ Friedrichsen; Tortzen (2001), pp. 19–20.
  6. ^ Mai-Britt Schultz; Rasmus Dahlberg (31 October 2013). Det vidste du ikke om Danmark (in Danish). Gyldendal. pp. 53–. ISBN 978-87-02-14713-1. I 1683 udarbejdede Ole Rømer en forordning, der fastsatte den danske mil samtenrækkeandre mål,hvilketvar hårdt tiltrængt, for indtil da havde derhersketet sandtenhedskaosi DanmarkNorge. Eksempelvis var en sjællandsk alen 63 centimeter, ... 
  7. ^ Poul Aagaard Christiansen; Povl Riis; Eskil Hohwy (1982). Festskrift udgivet i anledning af Universitetsbibliotekets 500 års jubilæum 28. juni 1982 (in Danish). Lægeforeningen. pp. 87–. En studie i Ole Rømers efterladte optegnelser, Adversaria, som hans enke Else Magdalene ... at give Christian V's kongelige mathematicus Ole Rømer (1644-1710) æren for udformningen af forordningen af 1.V.1683 ... 
  8. ^ Alastair H. Thomas (10 May 2010). The A to Z of Denmark. Scarecrow Press. pp. 422–. ISBN 978-0-8108-7205-9. ... although uniformity throughout the country was not achieved until statutes of 1683 and 1698, under the leadership of Ole Romer. The metric system was adopted in 1907 and is universal, though colloquially units such as tomme, tande land, ... 
  9. ^ Niels Erik Nørlund (1944). De gamle danske længdeenheder (in Danish). E. Munksgaard. pp. 74–. ... Maj 1683 gennemførte Reform af Maal og Vægt fastsatte Ole Rømer den danske Mils Længde til 12 000 danske Alen. 
  10. ^ K. Hastrup, C. Rubow, T. Tjørnhøj-Thomsen (2011). Kulturanalyse — kort fortalt (in Danish). Samfundslitteratur. pp. 219–. ISBN 978-87-593-1496-8. I Danmark blev den gregorianske kalender indført den 1. marts 1700 efter forarbejde af Ole Rømer. Man stoppede med brug af den julianske kalender den 18. februar, og sprang simpelthen de næste 11 dage over. så man landede direkte på ... 
  11. ^ Tom Shachtman (12 December 2000). Absolute Zero and the Conquest of Cold. Houghton Mifflin Harcourt. pp. 48–. ISBN 0-547-52595-8. ... down to an almost mythical point, an absolute zero, the end of the end. Around 1702, while Amontons was doing his best work in Paris, in Copenhagen the astronomer Ole Romer, who had calculated the finite speed of light, broke his leg. Confined to his home for some time, he took the opportunity of forced idleness to produce a thermometer having two fixed points ... 
  12. ^ Don Rittner (1 January 2009). A to Z of Scientists in Weather and Climate. Infobase Publishing. pp. 54–. ISBN 978-1-4381-0924-4. Fahrenheit's first thermometers, from about 1709 to 1715, contained a column of alcohol that directly expanded and contracted, based on a design made by Danish astronomer Ole Romer in 1708, which Fahrenheit personally reviewed. Romer ... 
  13. ^ Popularization and People (1911-1962). Elsevier. 22 October 2013. pp. 431–. ISBN 978-0-08-046687-3. ... letter from Fahrenheit to his Dutch colleague Hermann Boerhaave (1668–1738) dated 17 April 1729 in which Fahrenheit describes his experience at Rømer's laboratory in 1708. 
  14. ^ Neil Schlager; Josh Lauer (2001). Science and Its Times: 1700-1799. Gale Group. pp. 341–. ISBN 978-0-7876-3936-5. In 1708 Fahrenheit visited Ole Romer (1644-1710). Since at least 1702 Romer had been making alcohol thermometers with two fixed points and a scale divided into equal increments. He impressed upon Fahrenheit the scientific importance of ... 
  15. ^ Carl Sophus Petersen; Vilhelm Andersen; RIchard Jakob Paulli (1929). Illustreret dansk litteraturhistorie: bd. Den danske littterature fra folkevandringstiden indtil Holberg, af C.S. Petersen under medvirkning af R. Paulli (in Danish). Gyldendai. pp. 716–. ... Det var paa hans Tilskyndelse, at de første Navigationsskoler (i København og Stege) oprettedes, og Bestyrerpladserne besatte han med de bedste ... 
  16. ^ A. Sarlemijn; M.J. Sparnaay (22 October 2013). Physics in the Making: Essays on Developments in 20th Century Physics. Elsevier Science. pp. 48–. ISBN 978-1-4832-9385-1. The other, Ole Rømer, was Bartholin's amanuensis, later his son-inlaw. ... man, became the Danish king's mathematician (mathematicus regius), professor of astronomy at the University of Copenhagen, and eventually chief of police of that city. 
  17. ^ Denmark. Udenrigsministeriet. Presse- og informationsafdelingen (1970). Denmark. An official handbook. Krak. pp. 403–. ISBN 978-87-7225-011-3. It was perhaps fortunate that Ole Romer (1644-1710) was called home to Denmark after he had achieved world fame by ... of Copenhagen and oblige him to devote time and energy to thinking out measures against prostitution and begging. 
  18. ^ Gunnar Olsen; Finn Askgaard (1985). Den unge enevaelde: 1660 - 1721 (in Danish). Politikens Forl. pp. 368–. ISBN 978-87-567-3866-8. Det var et held, at Ole Rømer først blev kaldt tilbage til den danske hovedstad, efter at han i Paris havde opnået ... Men at denne geniale forsker som Københavns politimester skulle beskæftige sig med forholdsregler mod prostitution og betleri, .. 
  19. ^ Danmarks Naturvidenskabelige Samfund (1914). Ingeniørvidenskabelige skrifter (in Danish). Danmarks naturvidenskabelige samfund, i kommission hos G.E.C. Gad. pp. 108–. I de følgende Aar udstedtes der en Række Forordninger om Gaderne; de skyldes uden Tvivl Ole Rømer. Snart er det Brolægningen, det gælder, snart et omhyggeligt Reglement for Færdslen i Gaderne. Brolægningen havde medført store ... 
  20. ^ Svend Cedergreen Bech (1967). Københavns historie gennem 800 år (in Danish). Haase. pp. 246–. 1705-10 beklædtes politime- politimester ster-embedet af fysikeren Ole Rømer, i hvis embedstid mange reformer forsøgtes. Brolægning og belysning forbedredes, vandforsyning og vandafledning blev taget op til revision, men heller ikke en så ... 
  21. ^ Axel Kjerulf (1964). Latinerkvarteret; blade af en gemmel bydels historie (in Danish). Hassings forlag. pp. 44–. Ole Rømer vendte i 1681 tilbage til København, hvor han blev professor i astronomi ved universitetet og giftede sig med Rasmus ... justering af mål og vægt, blev ham betroet foruden ordning af byggeforhold, gaders brolægning og belysning. 
  22. ^ Virginia Trimble; Thomas R. Williams; Katherine Bracher; Richard Jarrell, Jordan D. Marché, F. Jamil Ragep (18 September 2007). Biographical Encyclopedia of Astronomers. Springer Science & Business Media. pp. 983–. ISBN 978-0-387-30400-7. 
  23. ^ Bobis, Laurence; Lequeux, James (2008). "Cassini, Rømer and the velocity of light" (PDF). J. Astron. Hist. Heritage 11 (2): 97–105. 
  24. ^ Teuber, Jan (2004). "Ole Rømer og den bevægede Jord – en dansk førsteplads?". In Friedrichsen, Per; Henningsen, Ole; Olsen, Olaf; Thykier, Claus; Tortzen, Chr. Gorm. Ole Rømer – videnskabsmand og samfundstjener (in Danish). Copenhagen: Gads Forlag. p. 218. ISBN 87-12-04139-4. 
  25. ^ Point H had occurred about one month earlier, according to Dieter Egger (1997-02-24). "Visualize Solar System at a given Epoch". Retrieved 2009-03-09. 
  26. ^ a b Saito, Yoshio (June 2005). "A Discussion of Roemer's Discovery concerning the Speed of Light". AAPPS Bulletin 15 (3): 9–17. 
  27. ^ Knudsen, Jens Martin; Hjorth, Poul G. (1996) [1995]. Elements of Newtonian Mechanics (2nd ed.). Berlin: Springer Verlag. p. 367. ISBN 3-540-60841-9. 
  28. ^ Huygens, Christiaan (8 January 1690) Treatise on Light. Translated into English by Silvanus P. Thompson, Project Gutenberg etext, p. 11. Retrieved on 2007-04-29.
  29. ^ Litteraturens Perioder (in Danish). Gyldendal Uddannelse. 2005. pp. 27–. ISBN 978-87-02-01832-5. En af deltagerne i enevældens storstilede forsøg på at skabe orden var Ole Rømer, der ikke blot var ... og i en periode borgmester i København, hvor han bl.a. fik skabt et effektivt brandvæsen og en ordentlig gadebelysning. 
  30. ^ Bent Rying (1974). Denmark: An Official Handbook. Press and Cultural Relations Department, Royal Danish Ministry of Foreign Affairs. pp. 661–. About the year 1700, the astronomer Ole Romer (1644-1710) displayed considerable technical activities as a public official ... knowledge to improving Danish streets and roads, harbours and bridges, water supplies, street lighting, and sewers. 
  31. ^ Meddelelser fra Ole Rømer-observatoriet i Aarhus. Observatoriet. 1958. pp. 177–. This extract from Ramus's thesis, together with his plate, shows clearly that Romer's Rota Meridiana was a meridian circle, taking this term in its modern meaning. The meridian circle was the final step in his series of instruments, in which ... 
  32. ^ William F. van Altena (22 November 2012). Astrometry for Astrophysics: Methods, Models, and Applications. Cambridge University Press. pp. 299–. ISBN 978-0-521-51920-5. The pursuit of better accuracy led Ole Romer to develop the meridian circle in 1690 which, with modifications, is still in use today. The meridian circle or transit circle (conceived at the end of the seventeenth century) was a combination of a ... 
  33. ^ Neil English (28 September 2010). Choosing and Using a Refracting Telescope. Springer Science & Business Media. pp. 6–. ISBN 978-1-4419-6403-8. With a similar telescope, the Danish astronomer Ole Romer, witnessing a timing glitch in the eclipse of a Jovian satellite, ... Romer is also credited for inventing the meridian transit circle telescope (usually just called the meridian circle), ... 
  34. ^ Frank Moore Colby; George Sandeman (1913). Nelson's Encyclopaedia: Everybody's Book of Reference ... Thomas Nelson. pp. 193–. The altazimuth (invented by Olaus Romer of Copenhagen in 1690) is available for measurements in all parts of the sky; and it was with a combination of this type, completed by Ramsden in 1789, that Piazzi made the observations for his great ... 
  35. ^ Hugh Chrisholm (1911). The Encyclopaedia Britannica: A Dictionary of Arts, Sciences, Literature and General Information. At the University Press. pp. 814–. Cassini, moreover, set up an altazimuth in 1678, and employed from about a “ parallactic machine,” provided with clockwork to enable it to follow the diurnal motion. Both inventions have been ascribed to Olaus Romer, who used but did ... 
  36. ^ Siegfried Schoppe (2012). Heinrich der Seefahrer, Kolumbus und Magellan: Planung, Versuch und Irrtum bei der Entdeckung der Neuen Welt durch Portugal und Spanien vor 500 Jahren (in German). BoD – Books on Demand. pp. 271–. ISBN 978-3-8482-0910-1. Der dänische Astronom Ole Römer (1644 – 1710) misst am Pariser Observatorium die Lichtgeschwindigkeit mit ... Das „Passage-Instrument“ setzt sich nicht durch, weil es für die Kapitäne zu kompliziert und nur bei klarer Sicht und ganz ... 
  37. ^ Nederlands Natuur- en Geneeskundig Congres (1927). Handelingen (in Dutch). 21-22. pp. 70–. ... slingeruurwerk van Huygens veranderde de zaak echter, en nu kon Ole Römer, de geniale Deensche astronoom, in 1689 een passage-instrument construeeren, dat in 1704 omgebouwd werd 
  38. ^ http://universitetsavisen.ku.dk/dokument2/dokument2/dokument7/Uni10.01.pdf/
  39. ^ John S. Rigden; Roger H Stuewer (29 May 2009). The Physical Tourist: A Science Guide for the Traveler. Springer Science & Business Media. pp. 62–. ISBN 978-3-7643-8933-8. Danish astronomer Ole Rømer (1644–1710) studied at the University of Copenhagen. ... from his home in Kannikestræde and at a new observatory built to the west of Copenhagen, now the site of the Ole Rømer Museum 
  40. ^ Nordisk universitets-tidskrift (in Danish). 1854. pp. 6–. ... den længe forhen af den Danske berömle Astronom Ole Römer forfærdigede Cirkel, hvilken han kaldte rota meridiana, ... Ophold paa hans saakaldte Observatorium Tusculanum i Landsbyen Wridslöse-Magte, nogle Mile fra Kjöbenhavn. 
  41. ^ Historiske meddelelser om København (in Danish). Københavns Kommune. 1936. pp. 316–. Trods Observatoriets nu saa fortrinlige og moderne Indretning synes Rømer dog ikke at have været helt tilfreds med Forholdene. Det er, saa vidt det ... Hvis vi undersøger de fleste af vore borgerlige Indretningers Historie, vil vi støde paa Ole Rømers Navn. ... Hans Elever har sikkert ogsaa observeret baade her og i det andet private »Observatorium tusculanum«, som han byggede sig i Vridsløsemagle. 
  42. ^ Carl Sophus Petersen; Vilhelm Andersen; RIchard Jakob Paulli (1929). Illustreret dansk litteraturhistorie: bd. Den danske littterature fra folkevandringstiden indtil Holberg, af C.S. Petersen under medvirkning af R. Paulli (in Danish). Gyldendai. pp. 716–. ... København og Roskilde, sit "Observatorium Tusculanum", som han med en klassisk Vending symbolsk kaldte det. 
  43. ^ København (in Danish). Gyldendal A/S. 2004. pp. 133–. ISBN 978-87-02-03645-9. Allerede Ole Rømer ( 1644 - 1710 ) var mere ambitiøs. Han syntes, der var alt for meget lys og røg i byen til, at man kunne se ordentligt, så han byggede sit eget observatorium i Vridsløsemagle langt uden for København. 
  44. ^ Skalk, nyt om gammelt (in Danish). Forhistorisk Museum. 1999. pp. xiv–. 
  45. ^ Historisk tidsskrift (in Danish) 106. Den Danske Forening. 2006. pp. 743–. Det var astronomen Claus Thykier, der havde fået den idé, at han ville finde det sted, hvor Ole Rømer (1644-1710) i 1704 ... I 1979 kunne Ole Rømer Museet åbne i lokaler på gården Kroppedal få hundrede meter fra fundstedet med Claus ... 
  46. ^ "Kroppedal | Gyldendal — Den Store Danske". Denstoredanske.dk. Retrieved 2015-10-05. 
  47. ^ Camilla Stockmann (2014-11-23). "Tycho Brahe-maleri er forsvundet" (in Danish). Politiken.dk. Retrieved 2015-10-05. 
  48. ^ Grethe Jensen; Benito Scocozza (1996). Politikens bog om danskerne og verden: hvem, hvad, hvornår i 50 år (in Danish). Politikens forlag. pp. 253–. ISBN 978-87-567-5697-6. 
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