Science and Engineering


Cycling Through Spacetime

Before it enters your eyes, light from stars you can see in the night sky has been traveling for tens, hundreds, or maybe thousands of years. Light's finite speed can sometimes lead to bizarre observations, particularly when light is coming from a moving object.

For example, in the 1600's astronomer Ole Rømer observed that Io, one of the Galilean moons of Jupiter, took varying amounts of time to complete one orbit. When Jupiter was moving away from Earth, Io's orbit was a little bit longer, and when Jupiter was approaching Earth, it clocked in a bit shorter.

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