Astronomy Bio...Ole Christensen Romer
Ole (or Olaus) Christensen Römer was born at Arhus, in Jutland, on September 25, 1644. He got his education in Copenhagen at the university, where he studied under the Bartholin brothers Thomas (1616-1680, professor of mathematics and anatomy) and Erasmus (1625-1698, physicist and astronomer). After studying mathematics and astronomy he became the personal assistant to Erasmus Bartholin, lived in his house and finally became his son in-law.
In 1671 Römer worked with Jean Picard (1620-1682), who had been sent by the French Academy to verify the exact location of Tycho Brahe's observatory. Picard was impressed by Römer's work and invited him to come back to Paris with him when the investigations were completed and Römer gladly accepted. After working at the Academy in Paris for one year as an assistant, Römer was made a member in his own right. He was also appointed to tutor the Crown Prince.
While in Paris Römer conducted his famous research that not only demonstrated that light travels at a finite speed but also its rate. Observing the satellites around Jupiter, especially Io, led him to notice that the length of time between eclipses of Io by Jupiter was inconstant. He found that when the distance between the Earth and Jupiter was least, the interval between eclipses was also smallest. He therefore measured the inter-eclipse period when the two planets were closest. In September 1679 he announced that the November 9th eclipse of Io by Jupiter would occur 10 minutes later than expected on the basis of all previous calculations. Römer's prediction was correct and his interpretation of the delay was a sensation. He explained that the delay was due to the time it took for the light to traverse the extra distance across the Earth's orbit when the positions of Jupiter and the Earth were such that they were not as close to each other as they sometimes were. This meant that light did not traverse space instantaneously, but traveled at a finite speed. Römer estimated that speed to be 225,000 km per second, which is remarkably close to the modern value of 299,792 km per second (considering that it was the first estimate ever). Not all of Römer's contemporary fellow astronomers, particularly those in France, accepted this interpretation of his observations. But sixty years after Römer's death it was confirmed by James Bradley (who was also able to improve upon Römer's estimate, obtaining a value of 294,995 km per second).
At the 1679 meeting of the Academy all of his work culminated with his calculation of the speed of light. With his newfound fame, Römer then went to England to meet some of the greatest astronomers of his age - Sir Isaac Newton, Sir Edmond Halley and the Astronomer Royal, John Flamsteed
Römer 's later work was on optics, instrument design and the systematization of weights and measures. Unsatisfied with the Copenhagen Observatory, he established his own private observatory which he named the Tuscalaneum and which possessed the first telescope attached to a transit circle, a device of his own invention.
In 1681 he returned to Denmark to take up the posts of Astronomer Royal to King Christian V and Director of the Royal Observatory in Copenhagen. He also accepted a number of civic duties. He died in Copenhagen on 23 September 1710.