CEN 511: Recent Discoveries in Astronomy

1. What are the major types of galaxies?
   1. What type of galaxy do we live in?
   2. What is the name of our galaxy?
   3. How many stars, roughly, are contained in our galaxy?
   4. What is the diameter of our galaxy?
   5. What is the thickness of the disc of our galaxy?
   6. What is the volume of the disc of our galaxy?
   7. What is the average density of stars in the disc of our galaxy?
2. Describe the three major pieces of observational evidence pointing to an expanding universe and a beginning from a Big Bang.
3. A galaxy located 100 Mpc away is moving away from us at what velocity? What redshift would it have? (HINT: you must select a value for Hubble's constant.)
4. Why is it suspected that most of the mass of the universe is not directly visible (the so-called dark matter)?
5. What is dark energy and what is the evidence for it?
6. Use the relation t = H₀^-1 to calculate the age of the Universe t in years, where H₀ = 65 km/s/Mpc is Hubble's Constant. This requires that you convert Mpc into km so the units match. We must also convert seconds into years. Since 1 Mpc = 3.1 x 10¹⁹ km, show that H₀ = 2.1 x 10^-18 s^-1 or about 6.6 x 10^-11 yr^-1. Now proceed to calculate t.