Speed of Light Physics Tshirt

The first true measurement of light-speed came in 1676 by a fellow named Olaf Roemer. He noted that the time elapsed between eclipses of Jupiter with its moons became shorter as the Earth moved closer to Jupiter and became longer as the Earth and Jupiter drew farther apart. This anomalous behaviour could be accounted for by a finite speed of light. He calculated that the speed of light was something like 2.14 x 10^8 metres per second. This measurement, considering its antiquity, method of measurement, and 17th century uncertainty in exactly how far Jupiter was from the Earth, is surprisingly close to the modern value of 2.99792458 x 10^8 metres per second. These modern values are obtained using devices called laser interferometers, which can very precicely pin down speeds and distances.