Ole Rømer

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Ole Christensen Rømer (Danish pronunciation: [o(ː)lə ˈʁœːˀmɐ]; 25 September 1644, Århus – 19 September 1710, Copenhagen) 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.

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General biography

Rømer was born 25 September 1644 in Århus to a merchant and skipper Christen Pedersen and Anna Olufsdatter Storm, daughter of an alderman. Christen Pedersen had taken to using the name Rømer, which means that he was from Rømø, to distinguish himself from a couple of other people named Christen Pedersen.[1] There are few sources on Ole Rømer until his immatriculation in 1662 at the University of Copenhagen, at which his mentor 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.[2]

Rømer was employed by the French government: Louis XIV made him teacher 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. Initially based on the Rhine foot, a more accurate national standard was adopted in 1698. 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).

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