Then answer to speed of light was discovered 340 years ago on this day, by Danish astronomer named Olaus Romer.
To honour Romer and the 340th year of his discovery of the determination of the speed of light, Google made a fascinating Doodle today. The animated Doodle shows how the study and the discovery came into being.
He determined the speed of light in 1676 by observing the planet Jupiter eclipsing its moon 140 times. His measurements were taken from Copenhagen while his peer Giovanni Domenico Cassini took measurements of the same eclipses in Paris. Romer compared the results to determine the speed of light.
Before Romer, famous astronomer, physicist and mathematician Galileo Galilei also tried to measure the speed of light. While Galileo failed to determine the speed of light, Ole Rormer succeeded.