Serway & Jewett — Universal Gravitation: Problem 37

Studies of the relationship of the Sun to our galaxy—the Milky Way—have revealed that the Sun is located near the outer edge of the galactic disc, about \(30\,000 \text{ ly}\) (\(1 \text{ ly} = 9.46 \times 10^{15} \text{ m}\)) from the center. The Sun has an orbital speed of approximately \(250 \text{ km/s}\) around the galactic center. (a) What is the period of the Sun’s galactic motion? (b) What is the order of magnitude of the mass of the Milky Way galaxy? (c) Suppose the galaxy is made mostly of stars of which the Sun is typical. What is the order of magnitude of the number of stars in the Milky Way?