The speed of light in vacuum is 299,792,485 metres per second- how do we know this? We have Danish astronomer Ole Romer to thank for this. And Google is commemorating this historic discovery with a creative doodle.
Today’s doodle celebrates the discovery made by Romer 340 years using an animated cartoon that depicts the inspiration that led the Danish astronomer into making the discovery.
But do you know the interesting story of how Romer determined the speed of life? If not, read on…
Apparently, Romer was studying one of Jupiter’s (the planet) moon Io when he noticed that the time between eclipses would vary throughout the year. Curious about his observation, Romer began taking notes about the timing of the eclipses.
As viewed from the Earth, eclipses of Io are observed in two ways:
– Io moves into the shadow of Jupiter and disappears.
– Io emerges out of the shadow of Jupiter and reappears.
Romer observed that as Earth orbited the Sun, it got away from Jupiter. And the time Io would come into view would lag behind the expected time written in his notes.
He theorised that this happened because the light reflected from Io wasn’t travelling instantaneously.
Unfortunately, most of Romer’s papers were destroyed in the Copenhagen fire of 1728. But one manuscript, that contained details about nearly sixty eclipses observed between 1668 and 1678, survived.
With the left over papers, Romer was able to conclude that it took light nearly 22 minutes to cross the diameter of Earth’s orbit around Sun.
Another scientist, Christian Huygens later converted this into simpler numbers and concluded that light travels at a speed of 220,000 kilometres per second.