Provide comprehensive answers to the following questions. Remember to support your arguments where necessary by websites and pictures.

1. How do long-exposure photos of two selected area of the sky reveal that galaxies are very common?

2. What is the difference between a Sa and a Sb galaxy? Between a So and-and Sa? Between a Sb and an SBb galaxy? Between an E7 and So galaxy?

3. How can collisions affect the shape of galaxies?

4. What evidence can you cite that galactic cannibalism happens?

5. What does evidence suggest that Sifter galaxies have suffered recent interactions with other galaxies?

6. How does the darkness of the night sky tell you something important about the universe?

7. How can Earth be located at the center of the observable universe if you accept cosmological principle?

8. Why can’t the universe have a center?

9. Why evidence shows that the universe is expanding?

10. Why couldn’t atomic nuclei exist when the age of the universe was less than 2 minutes old?