Ole Rømer's observations

Ole Rømer was a Danish astronomer who, in the late 17th century, made pioneering observations of Jupiter's moon Io. He noticed that the time it took for Io to orbit Jupiter varied depending on Earth’s distance from Jupiter. Rømer concluded that light has a finite speed, as the variations were due to the time taken for light to travel the varying distances. His work was crucial in showing that light doesn't travel instantaneously, which later laid the groundwork for understanding the speed of light in physics. This discovery marked a significant milestone in the study of astronomy and the nature of light.