Olaus Roemer

Roemer, Olaus (1644–1710), Danish astronomer, the first to show that light has a finite velocity. He noticed that Jupiter eclipsed its moons at times differing from those predicted and correctly concluded that the discrepancy resulted from the finite nature of light's velocity, which he calculated as 141 mi per sec (now calculated as about 186,282 mi per sec/299,792.458 km per sec).

See also: Astronomy.