Astronomers have found that light waves coming from a given point on the sun have a slightly higher frequency than light from a point on the opposite side of the sun. what do these measurements tell you about the sun’s motions? describe this phenomenon in terms of the concepts you have learned in this section. you may have to do some research.

The answer is that the sun rotates, so that one side is coming towards us and the opposite side is moving away from us. When a moving source emits a wave the frequency and wavelength of that wave change according to how fast it is moving, This is called the "Doppler Effect" and is used by police radar to tell how fast a car is moving. If the car is coming towards the radar, the frequency of the reflected radar signal increases, and if the car is moving away that frequency decreases. You can hear this yourself if you hear a car with its horn blowing go past you. As the car approached you the horn sounds higher than when it is going away from you. Using this method, we can look at stars many many trillions of miles away from us and tell how fast they rotate. 

Interestingly, our sun is not a solid object and gets twisted as it rotates. The equator of the sun rotates once every 25 Earth days, but near its poles it rotates more slowly at once every 29 Earth Days.

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