Answer:
It tells that the Sun is rotating.
Step-by-step explanation:
This phenomenon is a very good example of the Doppler's effect. According to the doppler's effect if an object is moving towards an observer the frequency of the wave emitted from the object will increase and if it is moving away from the observer, frequency will decrease.
Because of the same effect, when Sun is rotating, the light waves coming from the point which is moving towards the observer will have higher frequency than the light waves coming from the point which is moving away from us. Using the same phenomenon we can calculate the rotation period of the Sun and can also prove the differential rotation of the Sun.