Until 1676, it was believed that light was instantaneous. That year, the Danish astronomer Ole Roemer observed in the telescope that, compared to his calculations, there was a delay of 22 minutes in the eclipses of Jupiter’s moons. Roemer concluded that the delay corresponded to the time it took light from satellites to reach Earth, at a speed he estimated at 225,000 kilometers per second. “This value was very close to what is accepted today”, says physicist Giorgio Moscati from the National Institute of Meteorology (Inmet). The correct value – 299 792 km/s – was determined only in 1926 by the German physicist Albert Michelson. To arrive at that number, Michelson perfected, for 25 years, the interferometer, a device that measures the deviation of light reflected by rotating mirrors in fixed mirrors.
– What exactly is light?
– What is black light?