Please give clear, specific, and unambiguous answers.

Partial credit will be given on Question 1, but not on the short-answer questions (unless indicated otherwise).

Each short-answer question is worth 4 points. Fill in the blank, circle the letter for the correct answer, etc., as indicated.

Newton's gravitational constant, speed of light

1. In this question, we ask you to outline the principal events in the birth, life, and death of stars. Credit will be given for clear, specific, and correct answers.

(a) (2) What precedes the birth of stars in a cluster?

(b) (2) What triggers the events that lead to the birth of these stars?

(c) (2) Why does the matter become dense enough to form a star?

(d) (2) Why does the matter become hot enough to form a star?

(e) (2) What is the primary set of nuclear reactions in a young star?

(f) (2) At higher temperatures, in an older star, a different fuel must be burned in a different process. What is this fuel, and into what is it transformed through nuclear reactions?

(g) (2) Why does a star tend to become larger and emit a planetary nebula as it gets older?

(h) (2) What prevents an ordinary star from collapsing under gravity?

(i) (2) What prevents a white dwarf from collapsing under gravity?

(j) (2) What prevents a neutron star from collapsing under gravity?

2. (4) Two stars revolve around each other in a binary system, with a period of one month. Their masses are respectively 3 solar masses and 2 solar masses. What is their separation in astronomical units?

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3. (4) Which of the following might be left after a supernova? Circle all correct answers.

(a) white hole

(b) white dwarf

(c) black hole

(d) red dwarf

(e) neutron star

(f) neutrino star

(g) nebula

4. (4) What is your approximate Schwarzschild radius? Use an estimate of your mass in kilograms, with 1 kg corresponding to 2.2 pounds.

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5. (4) The turnoff point for a cluster of stars in the H-R diagram is

(a) the point at which giants turn of

(b) the point at which supergiants turn off

(c) the point at which white dwarfs turn off

(d) the point above which main-sequence stars are missing.

(e) the point above which there are only supernova remnants

(f) the point above which there are only dwarfs

(g) none of the above

6. (4) For this question, circle all correct answers.

In the H-R diagram

(a) luminosity is plotted as a function of density

(b) H is plotted as a function of R

(c) R is plotted as a function of H

(d) luminosity is plotted as a function of temperature

(e) the vertical axis represents absolute magnitude and the horizontal axis spectral type

(f) apparent magnitude is plotted as a function of distance

7. (4) List the following types of electromagnetic radiation in order of wavelength, with the longest wavelength at the top and the shortest wavelength at the bottom. [one point per correct answer]

radio waves, x-rays, infrared radiation, visible light

longest ___________________________________

next longest _______________________________

next shortest ______________________________

shortest __________________________________

8. (4) Which two of these four forms of electromagnetic radiation, listed in question 6, have the best chance of penetrating nebulae?

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9. (4) Reflection nebulae tend to have the color of the visible light that is most scattered. This is

(a) yellow

(b) blue

(c) green

(d) red

(e) brown

10. (4) The highest-velocity stars that an astronomer might observe have velocities of about 400 km/sec. What change in wavelength would this cause in the Balmer gamma line, which has an unshifted wavelength of 434 nm?

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11. (4) The sun has a surface temperature of about 6000 K, and it has a characteristic wavelength of about 500 nm. (This is the wavelength at which the intensity of the light it emits has a peak, when plotted as a function of wavelength.) What is the characteristic wavelength for a star with a surface temperature of 18000 K?

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12. (4) Light from the sun is yellow (or in the green part of the spectrum before allowance is made for atmospheric absorption). What is the color of a star with a surface temperature of 18000 K? [Just consider the visible part of the spectrum.]

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13. (4) There is a peak in sunspot activity on the sun every

(a) 80 years

(b) 132 years

(c) 3 years

(d) 450 years

(e) 11 years

14. (4) According to the Babcock model, the sunspot cycle is due to

(a) entangling of electric lines of force caused by the sun's rotation

(b) entangling of magnetic lines of force caused by the sun's rotation

(c) sudden convective upheavals in the photosphere

(d) sudden convective upheavals in the solar carona

(e) sudden inversions in the solar wind

15. (4) Which of the following are thought to be due to magnetic field events near the sun's surface? Circle all correct answers.

(a) fusion reactions

(b) radiative transfer

(c) solar flares

(d) solar prominences

(e) sunspots

16. (4) The dark matter makes up about what fraction of all matter?

(a) 2%

(b) 5%

(c) 10%

(d) 20%

(e) 30%

(f) 50%

(g) 90%

17. (4) What is the name of the whirling matter which forms a disk around a black hole, and which emits the detectable x-rays?

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18. (a) (3) What is the Chandrasekhar limit? I.e., what does this term mean?

_______________________________________________________________________________

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(b) (1) What is the value of the Chandrasekhar limit in solar masses?

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19. (4) What is the life expectancy of a star with a mass of 16 solar masses?

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20. (4) A solar flare can release joules of energy. How many one-megaton hydrogen bombs is this equivalent to? (One megaton corresponds to about joules.)

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21. (4) The pulsar in the Crab Nebula

(a) was left by supernova 1987A and rotates once every 33 seconds

(b) was left by supernova 1987A and rotates 33 times per second

(c) was left by the supernova of 1054 A.D. and rotates once every 33 seconds

(c) was left by the supernova of 1054 A.D. and rotates 33 times per second

(c) was left by Kepler's supernova and rotates once every 33 seconds

(d) was left by Kepler's supernova and rotates 33 times per second

22. (extra 4) As compared to the air in this room, the photosphere is

(a) thousands of times more dense

(a) about a hundred times more dense

(b) slightly more dense

(c) slightly less dense

(e) about a hundred times less dense

(d) thousands of times less dense

(e) none of the above