1.Liquid water is thought to be necessary for life. Where else in the solar system beyond Earth do we think there is liquid water? What keeps the water from freezing?

Europa at least, possibly the other Galilean satellites of Jupiter Callisto & Ganymede (NOT IO!). Tidal compression by the other satellites heat the interior. Although this isn’t strong enough to melt the ice originally, it is enough to keep it melted.

2.How long will the Sun have spent as a main sequence star when it finally begins to evolve toward the red giant phase? How long has it been on the main sequence to date?

About 9 billion yrs. Has been on MS 4.6 billion yrs, the same age of the Earth (which you should know, as informed people). I gave 0.5 partial credit for 2^nd if you got billions, no credit if you had Earth substantially younger (or older).

3.The mottled appearance of the whole solar surface is an indication of what physical process at work in the Sun? What other way can energy propagate outside the core of a star?

This granulation is formed by the top of convective cells. Heat is transported through most of the sun by radiation. Conduction is only appropriate for the sun’s core, once the C lattice forms.

4.There are two main types of supernovas. List which stars explode for each, the process that causes the explosion, and the results of the explosion.

Type Ia: WD accretes mass from binary star, pushing it over 1.4 Msun limit. C lattice melts & C ignites throughout core all at once, blasting star to bits w/o remnant.

Type II: massive star fuses elements all the way to iron, and then core catastrophically cools as iron fusion leads to gamma-photon release. Gamma photons destroy many elements lighter than iron, further absorbing energy. Energy loss leads to core collapse. High densities produce Weakons that convert protons+electrons to neutrons + neutrinos. Most luminosity goes out as neutrinos, cooling core further. Collapse ends when neutron star forms. Infalling star envelope bounces off neutron star, expands back into space. This shell is so hot that it fuses many elements beyond Fe. Neutron star may eventually appear to us as a pulsar if we are in its pulse beam, otherwise we see nothing.

5.The chemical composition of the surface layers of the Sun is determined primarily by what technique? How do we get information on the current physical conditions in the Sun's core?

Spectroscopy. Neutrinos

6.Any object will collapse under its own weight unless something stops it. In an ordinary star like the Sun, how is this collapse prevented today and how will it be prevented at the end of the Sun's life?

Today fusion reactions maintain interior heat & so pressure that resists gravity collapse. Later when these are done, the Sun collapses until the electron quantum effect pushes the C nuclei into an incompressible lattice.

7.Why is there such a thing as stellar parallax? What is it used for?

Because of the Earth’s orbit around the Sun, which gives us different vantage points on the stars during the year. Parallax allows us to measure distances of comparatively nearby stars.

8.Suppose that, at night, the brightness of a light bulb is measured from a certain distance and then moved to a distance twice as far away. How bright will it then appear, compared to the earlier measurement? 

1/2²=1/4.I gave only 1 point for this question. 0.5 point if you said that it was fainter farther away!

9.If the surface temperature of white dwarf stars is four times that of the Sun and energy output per unit area of a star depends on the 4th power of the temperature by the Stefan-Boltzmann relation, why then are white dwarfs intrinsically so faint?What is one way to make them MUCH brighter?

Luminosity depends on area (radius) of star as well as its temperature. You can make them brighter by dumping more mass on them, so that they nova (= fuse elements on their surfaces). Many of you said “bring them closer” which is technically correct but not really an answer!

10.What is the physical reason for the appearance of periodic splitting and recombining of spectral lines in the spectra of binary stars? What does this tell us about the stars?

Doppler effect. Their MASS!!(This is the ONLY way to get this info!)

11.In terms of nuclear reactions, what is the next stage of a star's life after the end of hydrogen burning in the core? What happens then to the outer layers of the star?

H shell fusion, which causes the star’s envelope to expand greatly.

12.Why does it require higher gas temperatures in the core of a star to produce nuclear fusion of helium compared to that required for hydrogen? What happens to the star if the core temperature increases in a short time?

He has +2 charge compared to +1 for H nuclei, so you higher collision speeds = T is required to overcome this electric repulsion. If the core T increases, the star’s thermostat kicks in to expand core, thereby reducing the fusion reaction rate, thereby loosing heat, thereby causing compression, etc.

13.What are the main byproducts of helium nuclear "burning" in red giant stars? How do these play a role in our lives?

C, O, … what we are largely made of or respire!

14.From observations of supernova explosions in distant galaxies, it is predicted that there should be four or five supernovae per century in our galaxy, whereas we have seen only about one every 300 years from Earth. Why is this? 

Not many of you got this, and I only took off 1 point for this question. The answer is in the reading, and it is that DUST along the line of sight scatters/absorbs the supernova light. Several of you pointed out that we should see a strong pulse of neutrinos!

15.A mass of about 2 solar masses is imploded inward by a supernova explosion. What will be the result of this implosion? What is the result if a mass of 8 solar masses is imploded?

WD is incorrect! Either a neutron star or nothing for 2 solar masses, black hole for 8. Note, I am giving you the CORE mass, not the mass of the whole star!

16.Suppose you are in a jet airliner traveling at a constant speed of 700 km/h in a constant direction. All windows are blocked so you cannot see outside, and there are no vibrations from the engines. What experiment can you do to determine that you are in fact moving relative to the earth's surface?

Actually, you are supposed to say that there is no way you can prove you are moving. However, several of you came up with ingenious techniques involving magnets that would do the job. Also, it is true that an EXTREMELY active atomic clock would show time dilation relative to one left on the ground.

17.In the LT diagram shown below, the brightest stars in the Pleiades cluster are not on the main sequence, but away from it toward the upper right. Why is this? What determines where a star sits on the main sequence? 

They are massive stars that have already evolved off the MS. Mass!!