It later had a definition dependent on a particular type of radiation. Today its definition depends upon the second and on the [[speed of light]] in a vacuum--which the CGPM now assumes to be constant. Thus a meter is 1⁄299,792,458th of a light-second. (Therefore the speed of light is exactly 299,792,458 meters per second.) | It later had a definition dependent on a particular type of radiation. Today its definition depends upon the second and on the [[speed of light]] in a vacuum--which the CGPM now assumes to be constant. Thus a meter is 1⁄299,792,458th of a light-second. (Therefore the speed of light is exactly 299,792,458 meters per second.) |