1) One important property of stars studied by Astronomers is the temperature. One way to determine the temperature is by studying the blackbody radiation coming from the star.

a) (6 pts) Name and briefly explain the two changes that happen to a star's spectral curve as its temperature rises.

b) (8 pts) Another way to determine temperature is by observing the ionization species present in a star's spectrum. Explain why the ionization species of an element is related to the temperature of the gas.

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

a) (3 pts) What are Fraunhofer lines? No explanation is needed here.

b) (6 pts) Briefly explain how Ernest Rutherford discovered the nature of the atom (what did he discover about atoms?). 1-2 sentences should be fine.

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

3) One of the prominent constellations in our night sky is Leo.

a) (7 pts) Name one of the bright stars in the constellation Leo and then give an altitude and azimuth (angle and direction along the horizon) for Leo that would tell someone where to find it from Fort Worth at about 10pm tonight. No explanation needed here.

b) (7 pts) Suppose you observe the spectral lines of Hydrogen in this star, and you find the lines to be very weak. How could you try to determine whether this weakness is due to a lack of Hydrogen in the star or something else?

4) The star Antares is located 150 light years from the Earth. Another star, Capella, is located 300 light years from the Earth. Neither star is moving relative to us here on the Earth.

a) (5 pts) Which of these two stars would you expect to have a larger parallax angle, assuming both are observed with the same baseline distance (Earth's orbit)? Justify your answer (a simple diagram may help).

b) (5 pts) Will the light from these stars be Doppler shifted? If not, why not? If yes, will the light be redshifted or blueshifted (and which one will be shifted more). Explain.

c) (4 pts) If Capella has four times the absolute luminosity of Antares, how will the apparent luminosities of the two stars compare numerically? Justify your answer fully.

5) An important energy source that we've studied in the first part of the course is nuclear energy, both fusion and fission.

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

b) (6 pts) We use nuclear fission on Earth to generate power. One isotope of Uranium, U-235 is very useful in nuclear power planets while Uranium-238 is not so useful. What's the difference between these two that makes U-235 more useful for power plants (and weapons)?

6) According to our theory, the interior of the Sun has a central core in which nuclear fusion takes place, a radiative zone just outside the core in which energy is transported outward from the core in the form of light (electromagnetic radiation), and a convective zone in which energy is transported outward mechanically.

a) (8 pts) Explain why energy is transported in different ways in the radiative and the convective zones.

b) (6 pts) Our fusion theory for the Sun's core was tested by observations of neutrinos here on Earth. We only observed about 1/3 of the expected number based on our calculations of the nuclear reactions that should be taking place in the core. What are two possible solutions to the "solar neutrino problem"? Explain both briefly.

7) This question deals with the Sun's corona.

a) (5 pts) Why is the corona so hot? Use conservation of energy to help explain why the corona is so much hotter than the Sun's photosphere.

b) (4 pts) What sort of spectrum would you expect to see if you were to observe the solar corona during a solar eclipse? Briefly explain your answer.

c) (4 pts) When Astronomers first observed the solar corona, they saw spectral line fingerprints they hadn't seen before, so they called this "new element" coronium. Later, we discovered that coronium is actually just an ordinary element from the periodic table observed under unusual conditions. What element is coronium (one example is fine)? No explanation needed here.

8) The star Pollux is four times more massive than the star Terebellum, and Pollux has a size (radius) that is twice that of Terebellum.

a) (6 pts) Determine numerically how the density of Pollux compares to the density of Terebellum. Justify your answer (show work).

b) (8 pts) Suppose the two stars have equal spectral line widths. What can you therefore conclude about the relative temperature of Pollux and Terebellum (which one is hotter)? Explain your answer fully.