In 1675, Ole Rømer measured the speed of light by
A) timing eclipses of Jupiter's satellites by the planet, which appeared to occur later when Earth was farther from Jupiter.
B) opening a shutter on a lantern on a hilltop and measuring the time taken for light from an assistant's shuttered lantern to return.
C) reflecting light from a mirror rotating at a known speed and measuring the angle of deflection of the light beam.
D) measuring how long it took the light to reach Earth from stars located at different distances from Earth.

Question

Quizplus · Accepted Answer

Ole Rømer measured the speed of light by observing the moons of Jupiter, specifically by timing the eclipses of Io, one of Jupiter's moons. He noticed that these eclipses appeared to occur later than expected when Earth was moving away from Jupiter and earlier when Earth was moving towards Jupiter, leading him to conclude that light takes time to travel from Jupiter to Earth.

In 1675, Ole Rømer Measured the Speed of Light by