See also: Römer (homonymy)

Ole Christensen Rømer (or Roëmer ) (September 25th, 1644 - September 19th 1710) astronomer Danish is a , which worked with the Observatoire of Paris as of 1671.

Biography

At the beginning of its career, Roëmer endeavoured to create new methods and to make observations with an aim of confirming the assumption of Copernic in connection with the stellar parallaxes. It also built models showing the rotation of the moons of Jupiter around this one, and the movement of the the Moon around the Ground.

In 1676, working on the eclipse S of the satellite Io of Jupiter, it noticed that these events occurred sometimes “at the hour envisaged” (its forecasts according to the laws of Kepler were checked), sometimes 10 minutes in advance and other times… 10 late minutes (Io carries out a revolution around terrestrial Jupiter in 1,77j, the shifts on a revolution was thus about 10 seconds, for a highher degree of accuracy, it calculated shifts over several years). It could find the explanation of this mystery, by considering the respective positions of the Earth and of Jupiter compared to the Sun. In September 1676, he announced that the eclipse of Io envisaged on November 9th would be done with 10 mn of delay. Success was complete, and a report was published in the newspaper of the scientists on December 7th. That made it possible to calculate the Speed of light: one arrived at the result of C = 212  000 km/s instead of 299  792,458 km/s is an error (relatively weak) of 29  %.

This first calculation speed of light follows work of Galileo, on this same question, which had given very bad results.

It also worked out the scale of temperature known under the name of scale Rømer.

At the time of its stay with Paris, it will occupy the very-honorary function of tutor of the Dolphin for Astronomy.

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