Ole Romer

In 1676 a thirty-two year old astronomer from Denmark stood up in the Academy of Sciences in Paris and announced that he had made a discovery. Some people in the scientific community, such as Newton and Halley, paid attention to him; some, like the director of the Paris Observatory, Giovanni Cassini, didn't. But what Romer had said was in fact of the most profound importance, not just to his field of work but to science in general.

Ole Romer had discovered the speed of light.

Born in Jutland in 1644, he studied under the Bartholin brothers who taught physics, mathematics and astronomy. During 1671, when Jean Picard travelled from Paris to do some work relating to Tycho Brahe's observations, Romer assisted him so ably that Picard took him back to Paris to work in the Academy. Rising quickly through the ranks, he became tutor to the Crown Prince and spent his time improving the accuracy of both observations and the instruments with which they were made.

His magnum opus, however, concerned eclipses of the innermost of Jupiter's moons, lo. Romer noticed that when Earth and Jupiter were farther apart, the eclipses took place later than when the two bodies were closer. The length of time it took for the event to happen was the same, but when Jupiter was close to us we saw it sooner than conventional wisdom said we should.

Romer realised that we could see the eclipse sooner than expected when Jupiter was closer, simply because Jupiter was closer. The light got here more quickly, just as two bullets fired at the same target from different distances won't arrive at the same time. The one fired from the gun closer to the target will obviously arrive first. The logical answer was that light must have a finite speed, just like everything else. The value he came up with was about 225, 000 Km/sec. which is pretty close to the actual speed of 300, 000 km/sec.

Well, obviously, says you. But it is only obvious because Ole Romer figured it out for us. Today, we take the fact that light has a finite speed for granted but in the Europe of the seventeenth century, many still assumed that light moved at infinite speed. People were still coming to grips with the fact that old assumptions, widely accepted without question, might not actually be true. It would be many years before Newton's Principia completed the triumph of the sceintific revolution.

Although his mentor, Picard, was among a number of influential names to support his findings, many in France were less impressed. The great Rene Descartes said that light travelled at infinite speed, as did Aristotle. Who was this Ole Romer anyway?

Eventually, Romer was appointed Astronomer Royal in his native Denmark, and even served a term as mayor of Copenhagen, but it would be another half a century before James Bradley's work on the abberation of light confirmed the truth of Romer's idea. Ole Romer died in 1710 aged sixty-six.

Return to Forgotten Astronomers Index Page