For the Physicists...
299,792.458 km/s is the speed of light in vacuum. However, according to Einstein's theory of General Relativity, the speed of light appears to vary with the intensity of the gravitational field. But 1400 years ago it was stated in the Quran (the book of Islam) that angels travel in one day the same distance that the moon travels in 1000 lunar years, that is, 12000 Lunar orbits / Earth day. Outside gravitational fields 12000 Lunar orbits / Earth day turned out to be the known speed of light!
We can calculate the speed of light by using information from verses of the Q'uran. Basically, the Q'uran was written at a time when people had no idea of what the speed of light was and many people thought that light had no speed and could travel at infinite speeds. The speed of light was discovered by Scientists after a very long time.