Concept explainers
Group Activity: Counting the Milky Way’s Stars. Work as a group to answer each part. Note: This activity works particularly well in groups of four students, with each student taking on one of the following roles: scribe: takes notes on the group’s activities; pro-poser: suggests tentative explanations to the group; skeptic: points out weaknesses in proposed explanations; moderator: leads group discussion and makes sure everyone contributes.
a. Work together to estimate the number of stars in the Milky Way from just these two facts: (1) the number of stars within 12 light-years of the Sun, which you can count in Appendix F, and (2) the total volume of the Milky Way’s disk (100,000 light-years in diameter and 1000 light-years thick), which is about 1 billion times the volume of the region of your star count.
b. Discuss how your value from part a compares to the value given in this chapter. Make a list of possible reasons why your technique may have underestimated or overestimated the actual number.
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Essential Cosmic Perspective
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