1. In fact, the Earth would appear to move a small bit in the sky from the near side of the moon, oscillating steadily around a single point in the sky.This motion is called 'libration'.Hypothesize why the Earth undergoes these small, comparatively subtle motions in the lunar sky.

2. Let's say we find 3 planets orbiting the star Zeta Capricornus (a real star);they are called Arnold, Betty and Charlie.If Arnold moves fastest about its sun (the star Zeta Capricornus),and Betty is slowest, and Charlie is in between, which planet is closest to the star? Which is farthest? Explain your reasoning.

3. Given that we do not see stellar parallax with the naked eye and that the eye can only make out angle as small as 2-3 arcmin, why does this place a lower limit of about 2000 AU on the distances to the stars?
4. Imagine that we devise a human spacecraft that can go 100 times faster than the Apollo spacecraft (This spacecraft required three days to go 400,000 km). How long would such a spacecraft require to reach Proxima Cen from Earth?
5. The angular diameter of the Moon is half a degree in the sky as seen from Earth. It is located an average distance of about 240,000 miles from Earth. From this information and using the small-angle formula, what is the true diameterof the Moon in miles?
6. Why can solar panels be used to power spacecraft that explore the inner Solar System (out to Mars), but not for the outer Solar System (from Jupiter on out)?
7. Use the new and improved version of Kepler's Third Law to determine what the Earth's orbital period would be if it orbited a star of twice the mass of the Sun but still at a distance of 1 AU. What would the period of the Earth be if it orbited a star of half the mass of the Sun? What would the period of the Earth be around a star of one solar mass, but if it were 0.5 AU from that star? What if it were 2 AU from a one solar mass star?
8. We saw that He makes up 8.5% of the total number of atoms in a typical sample of interstellar gas. What fraction of the mass of the ISM is made up by He? Keep in mind that each He atom weighs on average four times as much as each H atom. You can ignore the contributions of all other elements apart from H when you do this problem.
9. Explain why one cannot produce an H III ion.
10. Prove or convincingly explain why the series of emission lines of Hydrogen that involves transitions to the n = 1 orbit-known as the Lyman series-all have shorter wavelengths than all of the Balmer emission lines.The latter are the ones that terminate at the n= 2 energy level.
11. Photons with wavelengths shorter than 91 nm can ionize H atoms.What is the ionization potential-an energy-of the H atom?
12. Imagine that you observed a round molecular cloud and you used the Doppler  Shift to measure the radial velocities of different parts of the cloud. Describe how the pattern of inferred radial velocities over the face of the cloud would appear in the case of (a) a rotating cloud, and (b) and expanding cloud.
13. From 51 Peg how would the flux from the Sun change if the Sun's luminosity increased by a factor of two while its distance is unchanged? How about if the Sun's distance increased by a factor of two while the luminosity was unchanged?
14. An ionized Helium atom is nearly identical to a neutral Hydrogen atom except that the nuclear force is greater since there are two protons instead of one. Explain why absorption lines of ionized Helium are seen in the hottest Main Sequence stars only.
15. How long will the faint red Pleiades member HZ1306 live? Assume that this star is on the Main Sequence and has a luminosity of 0.05 that of the Sun. Be sure to use the proper branch of the Mass-Luminosity relation to answer this question. You can also assume that the lifetime of the Sun is10 billion years.
16. What is the proper motion of the Galactic Center due the motion of the Sun in its orbit?
17. Describe in reasonable detail how the motions (both proper motions and radial velocities) of the stars would appear if it were only the Sun that was orbiting the Galactic Center and all other stars were standing still.
18. The Sun just became a black hole. Of course, it gets dark without the sunlight. But what happens to the Earth's orbit? In particular,how does the orbit of the Earth after the Sun's collapse compare to the orbit before the Sun turned into a black hole? Assume that the Sun simply collapsed; that is, no mass was lost and nothing else fell into it to initiate the collapse.
19. For many centuries, astronomers understood that we lived in a disk-like Galaxy. But they thought we lived at the center of that Galaxy. What do you think is the principal reason for this fundamental error?