The Danish Astronomer Ole Christensen Rømer, was born on September 25, 1644, in Århus, Jutland and died on September 19, 1710, in Copenhagen, is recognized for his conclusive demonstration that light travels at a finite speed.
Rømer He traveled to Paris in 1672, where he spent nine years working at the Royal Observatory. The observatory’s director, Italian-born French astronomer Gian Domenico Cassini, faced a problem that had been studied long before by Galileo Galilei: how to use the periodic eclipses of Jupiter’s moons as a universal clock that would be a navigational aid. Cassini and his teammates discovered that the times between successive eclipses of the same satellite (for example, Io) show an irregularity that is related to the location of the Earth in its own orbit. The time between successive eclipses of Io becomes shorter as Earth approaches Jupiter and longer as Earth and Jupiter separate. Cassini had considered it, but rejected the idea that this could be due to a finite propagation speed of light.
In 1676, Rømer announced that the eclipse of Io scheduled for November 9 would be 10 minutes later than the time deduced based on previous eclipses of the same satellite. When events happened as he had predicted, Rømer He explained that the speed of light was such that it took – light – 22 minutes to cross the diameter of the Earth’s orbit. The Dutch mathematician Christiaan Huygens, in his Traité de la lumière (1690, “Treatise on Light”), used the ideas of Rømer to give a real numerical value to the speed of light – which was reasonably close to the accepted value today – although somewhat imprecise due to an overestimation of the time delay and some error in the then accepted figure for the diameter of the orbit of the earth.
In 1679 Rømer he went on a scientific mission to England, where he met Sir Isaac Newton and the astronomers John Flamsteed and Edmond Halley. Upon his return to Denmark in 1681, he was appointed royal mathematician and professor of astronomy at the University of Copenhagen. In the university observatory he installed an instrument with altitude and azimuth circles and a telescope that precisely measured the position of celestial objects. He also held various public offices, including that of mayor of Copenhagen in 1705.
Rømer He died as a result of a calculation, when he was 66 years old, on September 19, 1710.