1. Explain why the absorption lines of an element have the same wavelengths as the emission lines of that element.

2. Make up your own mnemonic to help you remember the sequence of spectral classes.

3. Why does convection develop about 70% of the way from the Sun's center to its surface?

4. What do we mean when we say that the Sun has a temperature of 5800K?

5. What evidence do we have that there is a relationship between sunspots and the temperature of the Earth?

6. What are radio and infrared radiation more useful than visible light in studying molecular clouds?

7. What evidence do we have that young stars are rounded by dusty disks rather than complete spherical shells of dust?

8. Why can't hydrogen fusion and helium fusion go on at the same time at the center of a star?

9. Suppose two single stars form at the same time. They have the same masses and chemical compositions. What can be said about the evolution of the two stars from that point forward?

10. In cluster 1, the main sequence extends from spectral class O to spectral class K. In cluster 2, there are no main sequence stars cooler than spectral class G. Which cluster is older and how do we know?