Measurement of the speed of light

Measuring the speed of light involves timing how long it takes for light to travel a known distance. Early experiments, like those by Fizeau and Foucault, used rotating mirrors or spinning wheels to reflect light over a measured path. Modern methods involve lasers and precise timing equipment. Since light travels extremely fast—about 300,000 kilometers per second—scientists use very accurate instruments to detect tiny time differences. These measurements not only determine the speed of light but also help define fundamental units in physics, such as the meter, which is based on how far light travels in a specific fraction of a second.