The Google doodle today shows a massive landmark in Science, the day we found the speed of light. This was done by Danish astronomer Ole Rømer in 1676. More recently Freddie Mercury would sing about travelling at the speed of light in the Queen song, Don’t Stop Me Now. He did have Brian May in the band who has a PhD in Astrophysics.

Going back to the serious business of light having a speed..How can light even have a speed? It is impossible to “see” light having a speed directly. Light just seems to instantaneously “be” everywhere as soon as the sun rises or a light switch is flicked on.

340 years ago, which is a long time ago now in the context of modern Physics, the Danish astronomer did work this out. His genius laid in the fact that he worked out a peculiar quirk in exactly when Jupiter’s moon Io popped into view through his telescope. It appeared to pop into view at different times at different times of the year. It shouldn’t have because celestial mechanics are very stable and steady indeed. He questioned the very assumption that light itself must be taking shorter or longer to get to the earth from Io. This is what the Google doodle shows today. Doing calculations with the speed of light are fairly standard at A Level Physics, but they also come up occasionally at GCSE Physics as well.

Professor Brian Cox explains this much better in his short video that I have linked below. So click away and learn about this big part of Scientific history.