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Chapter 23: Galaxies
1. It was not recognized until the mid 1920's that Galaxies were external to our own. Read about the Shapley-Curtis debate.
2. Hubble found Cepheid variable stars in nearby galaxies and was able to guess that these galaxies were far away.
3. Know the different kinds of galaxies?
4. What are elliptical galaxies? How do their shapes change as you go from E0 to E7?
5. How do the orbits of the stars in Elliptical galaxies differ from those in Spiral Galaxies?
6. What are dwarf elliptical galaxies? Are there any close to our own galaxy?
7. What is the range in size of elliptical galaxies?
8. What are the two major kinds of spiral galaxy? It is the gas, dust, and regions of young hot stars that make Spiral galaxies so beautiful.
9. Why do ellipticals and spirals differ in appearance?
10. Figure 17-10a is the LMC - the book calls it an Irregular galaxy but it does appear to be a barred spiral.
11. Read about the various distance methods for galaxies. The most used methods are Cepheid Variable stars for nearby galaxies and Type Ia Supernovae for very distant galaxies.
12. Know the definition of Look-Back time. It is the astronomer's "time machine".
13. What is Hubbles "law"? What did Slipher show and were did he do his work?
14. Know that Hubble's Law is related to the "age" of the universe -- the time since the Big Bang.
15. Galaxies show a large variation in size and brightness.
16. On pages 350-351 he shows some nice figures that illustrate galactic rotation curves. I have discussed this in earlier chapters to show that Dark Matter is found all over the universe.
17. He implies that measuring rotation curves is good only for nearby galaxies but doesn't define nearby. The larger the telescope the farther the galaxy that can be studied. What does the rotation curve of a galaxy show us?
18. Dark matter is not only found as part of galaxies but also is found in Clusters of Galaxies.
19. Galactic Cannibalism means that galaxies are colliding and merging into one larger galaxy. Our own galaxy will swallow the LMC and SMC.
20. How frequent are galaxy collisions? What part did collisions play in the formation of galaxies?
21. Remember that Galaxies come in groups.
22. What is the Local group? Roughly, how many galaxies are in the local group?
23. What and where is the Virgo Cluster?
24. Starburst galaxies are very bright because star formation is going on in them at a very high rate.
25. Superclusters are possibly clusters of galaxy clusters - or maybe not.
26. Figure 17-25 is a picture of the distribution of galaxies as measured by Margaret Geller. It shows Walls, Voids, and Filaments.
27. Read about the Origin and Evolution of Galaxies.
28. What is thought to have formed first - the galaxies or clusters of galaxies?
29. What is the local Supercluster?

Chapter 18: Active Galactic Nuclei
1. Galaxies with central Black Holes do strange and wonderful things.

Chapter 19: Cosmology
1. Read about Olber's Paradox. It is a question that has only recently been answered.
2. We assume that the Universe is Isotropic and Homogeneous: It will look the same from wherever we view it and on the largest scales matter is spread uniformly through out the Universe.
3. We also have evidence that the same physical laws hold throughout the universe.
4. The Cosmological Principle means that the Universe looks the same from wherever we are standing in the Universe.
5. The Universe is expanding and carrying the Galaxies along with it. Neither the Galaxies or clusters of Galaxies are expanding - local gravity overcomes the expansion of the Universe.
6. Read and try to understand the usefulness of the Raisin Bread Analogy.
7. The amount of mass in the universe shapes its curvature. Read about an Open, Flat, and Closed universe. It now looks like the Universe is Flat -- but that causes its own problems described later.
8. We live in a three dimensional universe (four including time) and there is no meaning to center or edge of the Universe.
9. We can use Hubbles Law and ask what happened to the Universe at the beginning. That is called the Big Bang. How do we know that it happened?
10. What is the 3 degree black body radiation? (Actually 2.7 degrees)
11. What is the Cosmic Background radiation? Who First proposed that it existed? What did Penzias and Wilson discover?
12. What happened in the first 200 seconds of the Big Bang? When did the Universe first become transparent to light?
13. When was most of the helium and deuterium in the universe formed?
14. If we ignore the latest developments - discovered since this textbook was written - then the amount of mass in the universe determines its ultimate fate.
15. What is meant by the critical density, what is the value given in class?
16. There is not enough Dark matter in the Universe to halt the expansion. (Dark matter doesn't matter)
17. We don't know what the Dark Matter is. Suggestions are WIMPS and MACHOS.
18. The Big Bang is a theory with a lot of supporting observational evidence. Nevertheless there are plenty of problems with our understanding.
19. For example, the latest observations of Type Ia Supernovae show that the speed of expansion of the Universe has changed over time. It is now accelerating and there must be some kind of energy producing this acceleration. Some people call it Dark Energy which produces a Dark Force. (Really!)
20. Skip The Quantum Universe.
21. What is the age of the Universe if H in Hubbles Law is: 70 km/sec/million parsecs?
22. Einstein introduced the Cosmological Constant. It now seems to be very important. Look at Figure 19- 18.
23. Skip the Origin of Structure. Some of the results are contradictory.
24. What is the ultimate fate of the Universe? As best we can tell!