Astronomers find that light emitted by a particular element at one edge of the Sun has a slightly higher frequency than light from that element at the opposite edge. What do these measurements tell us about the Sun’s motion?
The light from the side that has a lower frequency moving away from us this would be expanded in frequency due to doppler effect and light from the side that coming towards us should be compressed and increased in frequency.hence we should tell that sun is spinning. Or We can make an experiment to understand it.the light travels at various frequencies it will be illuminate on different colors spectrum called doppler effect.assume a blue shift indicates the higher frequency on the color spectrum and redshift indicates low frequency.from this astronomers are able to find detection of rotation and speed at which sun will spins.
