Quarter 1 Biography: Ole Roemer

Ole Roemer

            Ole Roemer was born in Aaruh, Denmark on September 25^th , 1644 and died in Copenhagen, Denmark on September 19^th 1710. Most of his adult life was spent in Copenhagen where he held a multitude of jobs, including astronomer royal, director of the observatory, master of the mint, inspector of naval architecture, harbor surveyor, ballistics expert, professor of mathematics at the University of Copenhagen, and the head of a commission which inspected highways. Despite all of these very prestigious jobs, he is best known for making the first accurate estimation of the speed of light. At this time in history very few astronomers even believed that there was a finite speed that light travelled at, most simply believed that it was instantaneous. Roemer was able to accurately determine the speed of light through very careful measurements over long periods of time. Roemer had his own observatory, the Tusculaneum, built between Copenhagen and Roskilde, which he filled with his own accurate instruments; he perfected the transit circle and is the first person to have attached a telescope to one. This observatory, in conjunction with the ground breaking instruments of that time allowed him to make very accurate observations of the heavens. He is alleged to have made just as many observations of Tyco Brahe, if not more. Roemer also had access to Brahe’s observations because he was appointed the editor of them by his brother Erasmus Bartholin. Brahe’s calculations were compounded by his own and with these 2 things Roemer was able to accurately calculate the speed of light, which was an amazing feat. The way that Roemer went about calculating the speed of light was through observations of the eclipses of Jupiter’s moons. He realized by looking at the observations of himself and Brahe that the eclipses either took place about 10 minutes earlier or later than they were predicted to, depending on the distance from the Earth to Jupiter. When Jupiter was closest to the Earth he noticed that they were about 10 minutes earlier than the calculations had predicted and while Jupiter was farthest away from the Earth he noticed that they occurred about 10 minutes later than they were predicted to. This led him to the realization that light had a finite speed, which few believed at that time. Because he now knew the difference in the time of the predictions that resulted because of the differing proximities of the Earth and Jupiter he was easily able to calculate the speed of light. His calculations stated that the speed of light was approximately 140,000 miles per second, which meant that the light coming from the Sun would take 11 minutes to reach the Earth. The current accepted speed of light is about 186,000 miles per second, or 8 minutes 20 seconds. This was an extremely close approximation for the first ever attempt at quantifying the speed of light and was clearly within an order of magnitude. The error that he experienced was caused by perturbations of Jupiter that he was unaware of at that time. Despite these findings, many people decided not to believe this fact and continued to believe that light had no finite speed. After this finding Roemer continued to do astronomical research along with his other multitude of jobs. Another creation that he isn’t famous for, but essentially designed is the thermometer. It was his idea to use the boiling point of water and the melting point of snow as the 2 base marks on a thermometer and it is alleged that he actually did more work on designing them than Fahrenheit did, but he is not known for this, which is why he is instead known as the person who first successfully approximated the speed of light.