In a vacuum, the speed of light is 186,282 miles per second. This is equal to 299,792 kilometers per second or about 670,616,629 miles per hour.
Attempts to calculate the speed of light have been going on for centuries. Aristotle believed that light traveled instantaneously, but another ancient Greek scientist, Empedocles, believed that light must take time to travel because light is capable of movement. Albert Michelson used an apparatus with a beam of light on a rapidly rotating mirror to measure the speed of light. Albert Einstein calculated that no matter how quickly an observer moves, light travels at the same speed, and that the speed of light does not vary with time or location.