Chapter 25, Problem 49A

Astronomers find that light coming from point A at the edge of the sun has a slightly higher frequency than light from point B at the opposite side. What do these measurements tell us about the sun’s motion?

To determine

Change in the sun’s motion when one edge looks shinier than the opposite one.

Answer to Problem 49A

It confirms that the sun is spinning.

Explanation of Solution

Introduction:According to the Doppler Effect, the frequency of the light increases when the source is moving towards the observer.

When point A at one of the edges of the sun looks shinier than another point B at the opposite side, then it would only dictate one possibility that the source is moving since the observer is stationary. Now, as the point A at one of the edge looks brighter compared to the opposite edge, it is because the sun is spinning on its axis.

Conclusion: Thus, the sun is spinning, that is why one edge looks brighter compared to the opposite edge.