some general Astronomy questions

1. What are the vernal and autumnal equinoxes?'What are the summer and winter solstices? How are these four events related to the ecliptic and the celestial equator? 2. How is an annular eclipse of the Sun different from a total eclipse of the Sun? what causes this difference? 3. How did Copernicus explain the retrograde motions of the planets? 4. why was the discovery of Neptune a major confirmation of Newton's universal law of gravitation? 5. Describe reflection and refraction. How do these processes enable astronomers to build telescopes? 6. Explain some of the advantages of reflecting telescopes over refracting telescopes. 7.What color will an interstellar gas cloud composed of hydrogen glow, and why? 8. Explain why the Doppler shift tells us only about the motion directly along the line of sight between a light source and an observer, but not about morion across the celestial sphere