Learn about the finite speed of light with this video segment adapted from Shedding Light on Science. In the 1600s, Galileo investigated the speed of light by conducting an experiment with lanterns, but he was unsuccessful in determining whether light had a measurable speed. It wasn't until later that Danish astronomer Ole Roemer calculated a finite speed of light by studying Jupiter's moon, Io. See animations illustrating these historical examples and also see how light appears to travel instantaneously in our everyday lives.