• # Galileo Galilei

Galileo came up with an experiment to measure light's velocity. He and his assistant took a shuttered lantern and they stood on hilltops one mile apart. Galileo flashed his lantern and as soon as his assistant saw Galileo's light he was supposed to flash his light. Galileo would then time how long it took before he saw the light from the other hilltop. This experiment didn't allow Galileo to come up with an estimated speed of light.
• # Ole Roemer

Ole Roemer was the first person to actually calculate the speed of light. Until this time, scientists assumed that light was either too fast to measure or infinite.
• # Ole Roemer's Experiment

Roemer measured the speed of light by timing eclipses of Jupiter's moon Io. In this figure, S is the Sun, E1 is the Earth when closest to Jupiter (J1) and E2 is the Earth about six months later, on the opposite side of the Sun from Jupiter (J2). When the Earth is at E2, the light from the Jupiter system has to travel an extra distance represented by the diameter of the Earth's orbit. This causes a delay in the timing of the eclipses. Roemer measured the delay and, knowing approximately the diame