Explorations: An Introduction to Astronomy (Arny), 7th Edition

Chapter 16: The Milky Way Galaxy

Thought Questions

1
What would the Milky Way look like in the night sky to an observer on a planet at the very edge of the Galaxy? What would it look like to an observer in the Galactic bulge?
2
Compare what happens in interstellar reddening to what occurs in our atmosphere at sunset. Does this also occur earlier in the day? What is different?
3
Knowing whether a selection effect is affecting your data is very important in astronomy. Imagine you were an alien visitor who only had an hour to study how long humans are babies, children, young adults, middle-aged, and elderly. Describe how your results would be affected by selection effects if you visited a shopping mall for an hour on a Wednesday afternoon in October, if you visited an elementary school, if you visited the mall at 9 p.m., or if you visited the mall on the weekend. What if instead you were studying human clothing, and you landed in Chicago or Florida in December?
4
Understanding possible selection effects is very important in polling to make sure results are accurate. If you were conducting a telephone poll about two presidential candidates, one of whom was more likely to appeal to older people and one more likely to appeal to younger people, what effects might you have to think about if you (1) could only call people with land lines (no cell phones), (2) could only call people with a cell phone, (3) could call both groups?
5
If you were explaining the density-wave theory to another person, what additional examples can you think of besides the slow car described in section 16.4 where a density- wave causes clumps of people, cars, or something else?
6
Cut four circles of cardboard whose diameters are 2, 4, 6, and 8 inches. Fasten them together through their centers with a brass paper fastener. Draw a circle about 2.5 inches in radius, centered near the edge of the 4-inch disk that marks all the disks. Now turn the circles in a way that reflects differential rotation. Use what you see to explain how self propagating star formation might make spiral arms.
7
Are spiral arms permanent structures? Explain, using the idea of the density-wave model in the book. What would happen to a spiral arm if the same stars stayed in it? (Consider how long it would take a star on the end of an arm to orbit once around compared to a star halfway in on the arm, if both have a velocity of about 225 km/sec).
8
How could we measure the mass of the Milky Way using a distant orbiting globular cluster?
9
How might you argue that there is a black hole at the center of the Milky Way, instead of, for example, a region filled with many neutron stars? What observations would help you rule out such a case?
10
What would the night sky look like if there were no dust or gas in the Milky Way, but the Galaxy were otherwise the same as it is today? What will the night sky look like when the Milky Way is very old and has used up all its star-forming materials?
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