Questions for Test #4

The material for the test will be found in chapters 5 and 6 (Paneck), Chapters 8 and 9 (Crowe) and the notes handed out during class

1. List three pieces of evidence that Harlow Shapley used to argue against the idea that spiral nebulae were external galaxies.
2. What were Curtis’ basic arguments in favor of the idea that spiral nebulae were external galaxies?
3. Explain how Shapley deduced that the sun is not the center of the Milky Way.
4. Explain how Cepheid variables were useful to Shapley in determining the distance to globular clusters. Why couldn’t he have used main sequence stars as “standard candles”?
5. How is the period of a Cepheid variable related to its absolute magnitude?
6. What is the “zone of avoidance”? How did the existence of the zone of avoidance seem to support the idea that spiral nebulae were part of the Milky Way?
7. How did Heber D. Curtis counter Shapley’s argument that the zone of avoidance implied that spiral nebulae were part of the Milky Way?
8. From today’s perspective of the “Great Debate”, in which ways was Shapley right and in which ways was he wrong?
9. From today’s perspective of the “Great Debate”, in which ways was Curtis right and in which ways was he wrong?
10. What key piece of evidence did Edwin Hubble find which effectively settled the “Great Debate”?
11. How did van Maanen’s rotation data for spiral nebula cast doubt on the idea that spiral nebulae were distant galaxies? How was the problem solved in favor of those who supported the external galaxy theory?
12. What three main things is Edwin Hubble remembered for?
13. Sketch and label Hubble’s “tuning fork” diagram for galaxies.
14. What did Hubble discover from studying the spectra of external galaxies?
15. The diagram below is a Hubble diagram which shows the relationship between the distances and recession velocities of galaxies. Label the x-axis and the y-axis and give the units. How did Hubble determine the y-axis value for each point? The x-axis value? How would you find the Hubble constant from this diagram?

16. Assuming a Hubble constant of 75, what is the distance in mpc of a galaxy receding at 10,000 kps?
17. Sketch and label the Bohr atom for hydrogen in the ground state.
18. What does it mean when we say that electron orbits (or energy levels) in atoms are quantized?
19. What problem presented by James Clerk Maxwell’s theory of electromagnetism was solved by quantizing the electron orbits of atoms?
20. What is meant by the term hydrostatic equilibrium?
21. How did Arthur Eddington use the fact that the sun is in hydrostatic equilibrium to show that the core of the sun must have a temperature of around 10 million K?
22. Briefly explain the source of the energy for the sun and stars. In other words, how do the sun and stars shine?
23. Why do the sun and stars produce energy at almost all wavelengths but planets do not?
24. Why was there no adequate theory of the sun’s energy source before the 20^th century? What was one popular explanation proposed by Hemholtz near the end of 19^th century?
25. Who was Cecilia Payne, in what era did she live, and what was her greatest contribution to astronomy?
26. Why do both very hot stars (type O) and very cool stars (type M) have very weak hydrogen lines in their spectra?
27. Why did Cecilia Payne come to the conclusion that about 90% of the atoms in the sun and stars are hydrogen?
28. Radio waves, microwaves, infrared, visible light, ultraviolet, x-rays and gamma rays are all part of the same phenomenon known as ________________. Where does this phenomenon originate? In what ways are microwaves different from visible light?
29. What led Vera Rubin to conclude that, although most of what we detect in the universe is hydrogen, there is an enormous amount of matter of an unknown nature that we don’t detect at any electromagnetic wavelength?
30. Large concentrations of neutral hydrogen in the Milky Way can’t be seen visually, but can be detected with radio telescopes. Since we can’t see it with our eyes, are these expanses of neutral hydrogen what we mean by dark matter? If not, how does it differ?
31. Why did Maxwell’s determination that electromagnetic waves always travel at a constant speed in a vacuum lead scientists to believe that there was way to determine the absolute frame of reference of the universe?
32. Einstein’s Special Theory of Relatively postulates that, for uniformly moving reference frames, the speed of light always come out the same regardless of where it is measured – the velocity of the source does not add to the speed of light. List the consequences of this theory for time, length, and mass for a body moving.
33. Why is “special” about the Special Theory of Relativity?
34. What is the principle of equivalence in the General Theory of Relativity?
35. What is gravity according to the General Theory of Relativity?
36. According to the General Theory of Relativity, what happens to time in a gravitational field?
37. In light of General Relativity, what exactly is expanding in the expanding universe discovered by Hubble?