× Sell your old school/college notes here at www.studyalways.com and make money for free
Ole Rømer, a Danish astronomer, calculated the speed of light by observing the eclipses of Jupiter's moon during the years 1668-1674. A discrepancy was observed for the time between the eclipses, increasing when the Earth was moving away from Jupiter and decreasing when the Earth was approaching. In half a year, there are a total of 102 eclipses of Io (Io is the innermost of the four moons of Jupiter discovered by Galileo in January 1610), giving a maximum delay of 16.5 minutes. Rømer interpreted this as the difference in the times needed for the light to travel between Jupiter and Earth. He obtained a value of 214,000 km/s compared to the current value 299,792 km/s. The diameter of the Earth's orbit was not accurately known then and there was also an error in the measurement of the delay. Nevertheless, it was a first confirmation that the speed of light is finite.