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Chapter 2: Q20DQ (page 538)

Stars other than our sun normally appear featureless when viewed through telescopes. Yet astronomers can readily use the light from these stars to determine that they are rotating and even measure the speed of their surface. How do you think they can do this?

Short Answer

Expert verified

There is a Doppler shift for the light which is used to calculate the rotation speed.

Step by step solution

01

Explanation

As the star rotates, assuming its axis doesn’t point straight at the Earth, one side moves away from us and the other side moves toward us. This shifts the received light toward longer and shorter wavelengths, respectively (so-called redshifts and blueshifts).

From the size of these shifts, astronomers infer the tangential speed of the rotating star, and from that, deduce the rotational speed.

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