The Science Fact on Instagram: "Ole Rømer calculated the speed of light by observing the moons of Jupiter, specifically the moon Io. Rømer noticed that the time between when Io disappeared behind Jupiter and when it reappeared was not constant, but instead varied depending on the position of Earth in its orbit around the Sun. Rømer reasoned that this variation in the time it took for Io to disappear and reappear was due to the finite speed of light. When Earth was closer to Jupiter, the time bet