Ole Rømer and the Speed of Light

Ole Rømer at work

On October 5, 1644 (or according to the old julian calendar September 25), Danish astronomer Ole Christensen Rømer was born. He is best known for making the first quantitative measurements of the speed of light.

Ole Rømer enrolled at the University of Copenhagen in the 1660s and learned from famous scientists like Rasmus Bartholin. Bartholin discovered double refraction of a light ray by Iceland spar and became famous through his very detailed descriptions. Unfortunately for him, light and its behavior was not very well understood back then and he was unable to explain these phenomena. However, Rømer learned alot by this man, who also let him stay at his home.

Another great influence to the young scientist Rømer was Tycho Brahe. His works on astronomical observations taught Rømer mathematics as much as astronomy and the well taught student was then able to start his firt job for the French government. For Louis XIV, Rømer took part in constructing the amazing fountains of Versailles and tutored. The following years, Rømer’s reputation grew and he was appointed Professor at the University of Copenhagen, also he married the daughter of Rasmus Bartholin. Only the loss of his observational work during the big Copenhagen Fire in 1728 meant a great setback. It was Rømer’s task to develop a national system for any kind of measurement, which was published in 1683 and he even managed to convince the king of introducing the Gregorian calendar, something Tycho Brahe attempted a long time before him.

Ole Rømer took part in several other achievements considering measurement. He developed a temperature scale that is now famous as the Fahrenheit scale. Fahrenheit improved and distributed his ideas after visiting Rømer. In his last years, he was even given the position as second Chief of the Copenhagen Police and invented the first street oil lamps in the city of Copenhagen.

Further achievements and inventions may be added to Rømer’s biography, like his innovative water supply system and his urban planning concept, but on this day he is mostly remembered as the first known person to achieve quantitative measurements of the speed of light.

The basics for his theories go back to Philip III of Spain and his prize offer to the scientist, who was able to develop a method if determining a ship’s longitude with no sight of land. Galileo Galilei managed the first steps. Unfortunately, Galileo’s methods was not thought of as very practical on a ship, but maybe on land. He started observing Jupiter just like Galileo and Cassini did the same in Paris. The differences of the eclipses were calculated and the longitude was measured. Rømer decided to go deeper into the topic and reasoned that the velocity of light was finite using the data of his observations and those of Christiaan Huygens. Unfortunately, this theory was not accepted until various publications by James Bradley in the 1720s.

Ole Rømer was honored multiple times during and after his adventurous life. He passed away on September 19, 1710.

At yovisto, you may enjoy a documentation on ‘Surpassing the Speed of Light‘.

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