The 340th anniversary of Ole Roemer's experiment to demonstrate the speed of light has been celebrated in a Google doodle. But who is the astronomer and how did he discover this significant measurement?
Who is he?
Ole Roemer was a Danish astronomer who calculated the speed of light. He was born in Denmark in 1644, studied in Copenhagen and was mentored by Rasmus Bartholin who discovered the double refraction of a light ray, and later worked for French government and Louis XIV as the tutor of the Dauphin. He became a professor of astronomy at the University of Copenhagen and in later life had an instrumental role in policing the city as well as creating a system of measurements.
What made him do it?
According to the American Museum of Natural History, Roemer was not trying to determine the speed of light when he discovered it. Roemer had instead been conducting his own work at the Paris Observatory into how to better measure the orbital period of Io, one of Jupiter’s four big moons, around its planet. He studied the orbit of Io over a number of years, marking the time that the moon became eclipsed by Jupiter. He noticed a difference in time in the eclipses from when the Earth was closest to Jupiter and when it was furthest away, and was then able to calculate the speed of light from these observations.
What else did he do?
Roemer achieved more than just determining the speed of light. He developed a temperature scale that divided the measurements between freezing water and boiling water into 60 degrees. He invented the mercury thermometer and in 1708 Daniel Gabriel Fahrenheit visited Roemer to see how he constructed his thermometers before creating his own and the Fahrenheit scale.
In Denmark, Roemer introduced the first national system of weights and measures, managed to persuade the King to introduce the Gregorian calendar and invented the first street lamps in in Copenhagen.
That’s quite an achievement – anything else?
In later life Roemer was appointed the second Chief of the Copenhagen Police and was instrumental in controlling the poor, beggars, the unemployed and prostitutes in the city, in addition to sorting out the water supply and sewers. He planned new pavements for the streets, worked to obtain new equipment for the fire department and planned new pavements. One of his first acts upon being appointed to the position was to fire the entire police force because he believed morale was alarmingly low.
