Encyclopædia Galactica Rami T. F. Rekola Tuorlan Astronomical Society Tuorla Observatory University of Turku

Speed of Light (c)

299,792,458 metres per second (about 300,000 km/s or 186,450 miles/s).

This is the speed at which light travels through empty space, i.e. vacuum. Light travel speed depends on medium through which it travels and is smaller than 299,792,458 m/s e.g. in water.