Light

Light is electromagnetic radiation of a wavelength that is visible to the human eye. In the electromagnetic spectrum, visible light has wavelengths which ranges from 400 nm to 700 nm, between ultraviolet and infrared light. This electromagnetic radiation consists of photons, which are massless particles of energy.

All electromagnetic radiation travel at the speed of light. In empty space, the speed of light is 300,000 km/second, that is to say 187,000 miles/second. Different physicists, such as Galileo and Ole Rømer, have attempted to measure the speed of light throughout history, but the more accurate measurement was performed by Leon Foucault in 1862 through an experiment using rotating mirrors to obtain a value of 298,000 km per second. Albert A. Michelson, however, refined Foucault's methods in 1926 using improved rotating mirrors to measure the time it took light to make a round trip from Mt. Wilson to Mt. San Antonio in California. The precise measurements yielded a speed of 299,796,000 km/s.