<human>: What are the different ways to measure the speed of light?
<bot>: 
1. The first way is to measure the time it takes for light to travel a certain distance and divide that by the time it takes an electromagnetic wave to travel the same distance.
2. Another way is to compare the frequency of two light sources, one moving away from the other at a constant speed, and calculate the difference in their frequencies over time.
3. A third way is to use a Michelson interferometer, which splits a beam of light into two beams, then recombines them after they have traveled different distances.
4. Finally, another method involves measuring the change in the phase of light waves as they pass through a medium with a known refractive index.