Chegg Textbook Solutions for Pathways to Astronomy 3rd Edition: Chapter 64

Chapter: Problem:

An interferometer measured the change in radius of one Cepheid as about 10% during its 10-day period. The star was measured to have an average radius of 40 million km. How fast was the surface of the star moving outward, on average, if it took 5 days to expand by 10%?

  • Step 1 of 1

    (About 9.3 km/s). A 10 percent increase in a 40 million kilometer radius is 4 million kilometers. So the surface of the star moved outward 4 million km in 5 days. There are 432000 seconds in 5 days, so the speed was 4 × 106 km/432000s = 9.3 km/sec.

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