21st Century Astronomy
21st Century Astronomy
6th Edition
ISBN: 9780393428063
Author: Kay
Publisher: NORTON
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Chapter 13, Problem 8QP
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Based on what you know about main-sequence stars, select all of the correct statements from the following list. 1. Since the interiors of stars cannot be observed, there are no theories about their structure. 2. More massive stars are hotter and brighter. 3. The weight of a star must be balanced by internal pressure. 4. More massive stars live longer; they take longer to use up all their energy. 5. Stars change position on the main sequence throughout their lives. 6. Outward energy flow in a star is by conduction only.
Absorption lines produced by interstellar gas   a. are wider than the lines from stars because the gas is hotter than most stars.   b. are more narrow than the lines from stars because the gas has a lower pressure than stars.   c. indicate that the interstellar medium contains dust.   d. indicate that the interstellar medium is expanding away from the sun.   e. indicate nothing; none of the above statements are true.
The place on the H–R diagram where contracting protostars first become visible is   a. the horizontal branch.   b. the instability strip.   c. the birth line.   d. the zero-age main sequence.   e. none of the above.
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