Ole Rømer

Ole Rømer
Ole Rømer, portrait by Jacob Coning from c. 1700
Born	Ole Christensen Rømer (1644-09-25)25 September 1644 Århus, Denmark–Norway
Died	19 September 1710(1710-09-19) (aged 65) Copenhagen, Denmark–Norway
Nationality	Danish
Fields	Astronomy
Alma mater	University of Copenhagen
Known for	speed of light
Signature

Ole Christensen Rømer (Danish pronunciation: [ˈo(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.

Rømer also invented the modern thermometer showing the temperature between two fixed points, namely the points at which water respectively boils and freezes. In scientific literature alternative spellings such as "Roemer", "Römer", or "Romer" are common.

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. 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. There are few records of Ole Rømer before 1662, when he graduated from the old Aarhus Katedralskole (the Cathedral school of Aarhus), 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.

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.