Conversion Center

Mile per hour (mph or mi/h) is a unit of velocity equal to 0.44704 m/sec. This traditional unit is based on the statute mile.

Speed of light (c) in vacuum is equal to 299 792 458 meters/sec with a relative measurement uncertainty of 4 parts per billion. Up to 17^th century humanity wasn't sure if light was transmitted instantaneously or simply very quickly. The Danish astronomer, Ole Christensen Rømer first demonstrated that light travelled at a finite speed when he studied the apparent motion of Jupiter's moon Io.