Learning Goal: I’m working on a astronomy discussion question and need an explanation and answer to help me learn.

Ch. 16 Study Questions

1. About how many stars are there in the Milky Way Galaxy?

2. Why are Cepheid variable stars useful?

3. What is interstellar extinction?

4. How did Shapley estimate the location of Sun in the Milky Way?

5. Why do astronomer observe 21 cm radio waves to probe the far reaches of the Milky Way?

6. Which components of the Milky Way are the best tracers of spiral arms?

7. What is the diameter of the Milky Way?

8. The presence of what type of object accounts for the very fast orbiting of stars and gas about the center of the Milky Way?

9. Dark matter has been invented to explain a hard-to-understand feature of the Milky Ways rotation. What is that problem feature?

10. Where in the Milky Way do we find the very oldest stars?

Ch. 17 Study Questions

1. What can you say about the size of the nucleus of a spiral galaxy, if the arms are very loosely wound?

2. What is the name of the mechanism believed to produce grand-design spirals?

3. What galaxy type is full of gas and dust? What type is not?

4. What galaxy type is mostly made of old stars?

5. What galaxy type is still undergoing star formation?

6. About how many galaxies are in our own “Local Group?”

7. How do giant ellipticals get so BIG?

8. In a typical cluster of galaxies, what percent of the matter present is luminous (visible)?

9. What is the best evidence that the universe is expanding?

10. In the expanding universe, what is expanding? Atoms? The Solar System? Stars? Galaxies? Something else?