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Astro*Dictionary by Michael Erlewine





1 article for "Roemer, Olaus"

Roemer, Olaus [Astro*Index]

(roi'mer) (1644-1710) Danish astronomer. Born at Arhus, Jutland; died at Copenhagen.

Picard visited the old observatory of Tycho Brahe in order to determine its exact longitude and latitude; while in Denmark, he engaged Roemer as an assistant, and convinced him to come to Paris. There Roemer carefully observed the motion of the satellites of Jupiter, using the times supplied by Cassini's tables of the motions of Jupiter's moons, predicting the exact moment when each moon would be eclipsed by Jupiter. He found that during the periods when the Earth was approaching Jupiter, the eclipses occurred too early, and when the Earth was receding from Jupiter, the eclipses were too late. From this information, he was able to determine that the velocity of light was not infinite (as Aristotle and Descartes had claimed) but was finite, and he provided the valueof 227,000 kilometers per second (the modern valus is 299,792 km/s). This finding is of critical importance to the further development of astronomy and in the theories of Einstein.

See also:
♦ Picard, Jean ♦ Brahe, Tycho ♦ Cassini, Giovanni Domenico ♦ Gravitation ♦ Light, Velocity of


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