• QUESTIONS BEFORE LECTURE 28

now think about these

• Why is it important to build different types of telescopes?
• Why is it important that some types of telescopes be above the atmosphere?
• Define open, closed, and just on the boundary universes in terms of expansion, curvature, mass density, and mass density parameter Omega.
• What is the total energy of the universe for open, closed, and just on the boundary?
• Which way do you want it to be: open, closed, or on the boundary? Why?
• What happens to a star which runs out of nuclear fuel? List the stages, then the three possible outcomes.
• Characterize a black hole by its mass density, curvature, time, path of light.
• Why is the force of gravity huge near a black hole?
• How do we observe black holes? After all, you can't see them!
• What is there about galaxies that makes us certain there is ten times as much matter in them as is visible, that is, 90 percent of the universe is made of dark matter?
• How do we observe dark matter? After all, we can't see it!
• Relate dark matter to the Copernican Revolution. (This is a serious question.)