500 kroner - Ole Rømer - The speed of light

In 1675, during a stay in France, Ole Rømer was the first scientist to prove that light is not propagated instantaneously, but at a finite speed. As he put it, light "hesitates". Ole Rømer calculated that it took between 8 and 11 minutes for light from the sun to reach the earth. The time is in fact 8 minutes and 20 seconds, so Ole Rømer was able to perform a very exact measurement. A few years after his discovery, in 1681, Ole Rømer was called back home to Denmark by King Christian V to take up a position as professor of astronomy and head of the Rundetårn (Round Tower) observatory in Copenhagen. Ole Rømer did not only work as a scientist. In the 1680s he introduced uniform weights and measures throughout Denmark. He also held a number of positions as chief of the police and of the fire department and mayor of Copenhagen, and for some time he served as a supreme court judge. It was also thanks to Ole Rømer that Denmark in 1700 adopted the Gregorian calendar.