The speed of light is the invariant speed of every inertial frame and the limiting speed of causal propagation in special relativity.
A light-second is a unit of length: the distance vacuum light travels in one second. It is useful in a spacetime diagram because a time of one second corresponds to a coordinate of one light-second, making the slopes of the light cone particularly easy to read. The unit is a distance, rather than an elapsed time.
Articles by others on the same topic
The speed of light in a vacuum is approximately **299,792,458 meters per second** (about **300,000 kilometers per second** or **186,282 miles per second**). This speed is considered a fundamental constant of nature and is denoted by the symbol **c**. It plays a crucial role in physics, particularly in the theory of relativity, and affects concepts such as time, space, and energy.
