Hearing so much about the speed of light, made us take the notion for granted. It is a basic constant of the Universe that says light travels at that magnificent speed because of the way the Universe functions, and that’s it.
Outside of the world of astronomy and high-energy particle physics, light seems to be spontaneous. Or at least, that is what our ancestors have assumed. This changes in the late 1600s, when astronomer Ole Romer released a bunch of observations. He discovered the fact that something was not ‘right’ with light after he analyzed Io, the first moon of Jupiter.
At regular intervals, Jupiter and its moon would line up, and the planet would no longer allow researchers to see Io. The process continues every few days over the course of a year.
Cracking the Peculiar Pattern
Romer then observed something peculiar about the eclipses of Io: sometimes, they were taking place with a bit of a distance between them, and sometimes, they were a little closer. After a few years, the astronomer elucidated the mystery. Apparently, when the Earth was moving closer to Jupiter, the eclipses of Io got closer together, and when the Earth‘s orbit around the Sun was moving away from the gas planet, the eclipses were more distant.
However, the only way to solve the mystery was for light to have limited speed. If the scientists were to observe an eclipse of Io in a particular position of Earth‘s orbit, and if we happen to distance from Jupiter, the next eclipse would occur a bit later. That happens because we have to wait for the occurrence of the eclipse, and the time it takes for light to travel the additional distance the Earth has made. The reverse happens when moving closer to the gas planet as well.
From these findings, Romer could estimate the speed of light. He stated it to be 220,000 km/s, which is not that different than the modern value of 299,792 km/s.