One of the most important discoveries in this century is that the galaxies all appear to be moving away from each other. Astronomers take this observation as evidence that the universe is expanding. 
Explain the scale on which the universe is expanding. 
Is your home, the Earth, or our Solar System expanding? Why or why not?

In the late 1990s, observations of a specific type of supernovae (Type Ia supernovae, to be exact) made a significant change in our understanding of the expansion of the universe. 
Given what you know about supernovae and what is discussed in your textbook, can you say what properties of the supernovae allow them to serve as unique tracers of the distant universe? 
What surprising discovery was made based on observations of these supernovae, and how did it change our understanding of the universe? 

The Big Bang theory of the universe, which explains the expansion of the universe, also implies that the universe had a beginning in time. 
How do we estimate the age of the universe? What was the old controversy among astronomers about the age of the universe, and how was it resolved?