Rømer's determination of the speed of light
= Rømer's determination of the speed of light
{wiki=Rømer's_determination_of_the_speed_of_light}
Ole Rømer, a Danish astronomer, is credited with the first quantitative measurement of the speed of light in the late 17th century. In 1676, Rømer observed the motion of Jupiter's moon Io and noted variations in its orbital period depending on the Earth’s distance from Jupiter. He realized that these discrepancies were due to the finite speed of light.