Speed of Light
Date: 1993 - 1999
How do you measure the speed of light?
Since light moves very fast, you either need to measure its motion over
a very long distance, or else you need to be very fast about it. The first
measurements (including one based on the orbits of the moons of Jupiter) used
the long-distance approach, but with modern very fast clocks and other technolog y it's not that hard
to measure the few nanoseconds it takes for light to travel a certain distance.
Actually, nobody ever has to measure the speed of light again because it's been
established as a constant that is used to define the metric unit of length (the meter) in terms
of the unit of time (the second) which we can measure much more precisely.
Click here to return to the Astronomy Archives
Update: June 2012