1) Astronomers use many different kinds of telescopes to observe stars. This question deal with some of the issues involving telescopes.

a) (4 pts) Most Astronomers observing stars in optical (visible) wavelengths tend to use reflecting rather than refracting telescopes. Briefly explain one reason why reflecting telescopes are preferable.

b) (5 pts) Radio telescopes are often used, despite their poor resolution, to observe regions in which new stars are being formed. Briefly explain one reason we use radio telescopes for this research instead of optical telescopes.

c) (5 pts) Describe how interferometry can be used to greatly improve the resolution of radio telescopes (why does the resolution increase with this method?).

2) The photosphere of the Sun represents the outermost layer of the envelope, from which light can finally escape the Sun.

a) (6 pts) Briefly describe the temperature structure of the photosphere (is it hotter near the base, near the top, constant temp throughout?, etc.), and explain how limb darkening shows us this structure.

b) (4 pts) Briefly explain the physical (observed) evidence that tells Astronomers that sunspots in the solar photosphere are correlated with strong magnetic fields.

c) (4 pts) Describe how the locations of sunspots change over the course of an 11-year sunspot cycle.

3) Suppose we are trying to find the distance to a star (Deneb) that is beyond the reach of parallax measurements.

a) (5 pts) Why is the parallax method of distance determination limited to only nearby stars? Explain.

b) (5 pts) Briefly describe how you could use the inverse square law to determine the distance to this star, assuming it has all of the same spectral characteristics as the Sun.

c) (4 pts) Suppose you see a star (Markab) that measuring techniques reveal is about half the distance to Deneb. The absolute luminosity of Markab is found to be about twice that of Deneb. Numerically, how does the apparent luminosity of Markab compare to that of Deneb. Justify your answer fully.

4) This question deals with our attempts to determine the properties of stars (such as temperature, size, radial velocity, distance and composition).

a) (4 pts) One satellite that gave us a lot of information about some stars was Hipparcos. What was the purpose of the Hipparcos satellite (what was it trying to measure)? No explanation needed here.

b) (10 pts) To determine the composition of this star, we would measure the strengths of its spectral lines, but sometimes spectral lines can be weak even when the abundance of an element is high. For example, Hydrogen lines are weak in very cool and very hot stars. Explain why in each case.

5) One important property of stars studied by Astronomers is the temperature. One way to determine the temperature is by studying the ionization species in the star's spectrum.

a) (8 pts) Explain why the ionization species of an element is related to the temperature of the gas.

b) (6 pts) Another way to determine the temperature is by observing the blackbody radiation coming from the star. Name and briefly explain the two changes that happen to a star's spectral curve as its temperature rises.

6) One of the prominent constellations in the night sky is Canis Major.

a) (7 pts) Name one of the bright stars in the constellation Canis Major and then give an altitude and azimuth (angle and direction along the horizon) for Canis Major that would tell someone where to find it from Fort Worth at about 10pm tonight.

b) (7 pts) Suppose we were to deduce that this star has spectral line widths identical to our own Sun, but observations of ionization species tell us that the Sun is only about half the temperature of the star in Canis Major. What could you then conclude about the relative sizes of the Sun and this other star? Justify your answer fully.

7) Three scientists who have made great contributions to Astronomy are Cecilia Payne, Hans Bethe and Ernest Rutherford. This question asks about their discoveries.

a) (4 pts) Briefly state something important that Cecilia Payne discovered about stars.

b) (5 pts) Briefly explain Hans Bethe's contribution to our understanding of the Sun.

c) (5 pts) Briefly describe what Ernest Rutherford discovered about the nature of atoms, and explain how he discovered it.

8) One big problem confronting the world today is energy production. Due to finite reserves of fossil fuels and problems with other energy sources, many scientists are trying to make nuclear fusion a practical reality. If they succeed, we could potentially have limitless energy with very little pollution associated. Unfortunately, fusion doesn't happen very easily in our labs here on Earth.

a) (8 pts) Explain why both high temperature and high density are needed in order for nuclear fusion to take place (whether in the Sun or in a nuclear fusion reactor).

b) (6 pts) Instead of using ordinary Hydrogen like the Sun uses, our fusion experiments involve Deuterium and Tritium. How are these ingredients different from ordinary Hydrogen, and what's the advantage to using these two ingredients as opposed to other options?