PH109 Exploring the Universe, Test #3, Fall, 1999
NAME______
Please indicate the best answer to the following questions on the answer sheet provided. Please answer the essay questions directly on this handout. All questions are worth 2 points unless noted otherwise.
1. A measurement of the parallax of a star allows us directly to determine the star's
a) rotation rate, b) temperature, c) distance, d) age
2. By what factor would the brightness of a star increase if an observer moved from 3 parsecs to 1 parsec from the star?
a) 3 times, b) 9 times, c) 27 times, d) 81 times
3. The absolute magnitude of a star is a measure of its
a) distance, b) temperature, c) mass, d) luminosity
4. The difference between the apparent magnitude and absolute magnitude of a star is a measure of the star's
a) luminosity, b) temperature , c) brightness as we perceive it, d) distance
5. How do the Sun, a white dwarf, and a red giant rank in descending order of luminosity?
a) Sun, white dwarf, red giant, b) red giant, white dwarf, Sun
c) red giant, Sun, white dwarf, d) white dwarf, Sun, red giant
6. Which of the following can produce a continuous spectrum?
a) a cold gas at low density, b) a hot gas at low density
c) a gas consisting entirely of molecules, d) a hot solid
7. What will be the spectrum of a cool, tenuous gas with a hotter 'black body' behind it.
a) absorption lines only
b) continuous radiation only
c) continuous radiation with emission lines superimposed
d) continuous radiation with absorption lines superimposed
8. Suppose the electron in an atom is in an excited orbit. What will happen to the electron if nothing disturbs the atom?
a) it will remain in the same excited orbit
b) it will fly away from the atom, ionizing the atom
c) it will move to the lowest energy orbit
d) it will move to another excited orbit which has higher energy
9. The property of a star which determines its spectral class is its
a) chemical composition, b) temperature, c) radial velocity, d) rate of rotation
10. The spectral classification scheme, OBAFGKM, is correctly interpreted as a sequence in stellar
a) distance, b) size, c) age, d) temperature
11. An HR diagram for a group of stars can be produced by plotting their
a) masses versus ages, b) magnitudes versus spectral types
c) temperatures versus colors, d) distances versus luminosities
12. Why are there more main sequence stars than giant stars?
a) the main sequence stage for a star is longer than the giant stage
b) giants are dim and hard to see
c) most giant stars are drawn to the core of the galaxy
d) few stars first form as giants rather than main sequence stars
13. Hydrostatic equilibrium describes the balance between
a) mass and luminosity, b) pressure and gravity
c) temperature and density, d) radius and luminosity
14. The four hydrogen nuclei which are fused together are more massive than the helium nucleus which they make. What happens to the missing mass?
a) it is converted to energy, b) it is ejected from the star in flare activity
c) it reappears later as neutrinos, d) it is resupplied to the Sun by meteoroid impacts
15. Approximately how long is the main sequence lifetime of the Sun?
a) 10 billion years, b) 1 billion years, c) 100 million years, d) 10 million years
16. The Sun will run out of fuel in about
a) 5 trillion years, b) 5 billion years, c) 5 million years, d) 5 thousand years
17. The two most abundant elements in the Sun are
a)hydrogen and helium, b) iron and silicon
c) nitrogen and oxygen d) hydrogen and oxygen
18. The temperature at the surface (photosphere) of the Sun is about
a) 1000K, b) 5000K, c) 10,000K, d) 50,000K
19. Why do sunspots appear dark?
a) they emit no light
b) they are transparent and let us see deeper, darker layers
c) they are cooler than their surroundings
d) they are shadows
20. The least massive stars in which nuclear fusion occurs have masses of about 8 percent that of the Sun. Why don't less massive objects ever experience nuclear fusion?
a) they explode before fusion can begin
b) they collide with other objects and increase their masses
c) they never become hot enough for fusion to occur
d) they become black holes before fusion can begin
21. What is the general name for stars which are converting hydrogen into helium in their cores?
a) main sequence stars, b) red giant stars, c) white dwarf stars, d) protostars
22. The most important factor affecting a star's main-sequence lifetime is
a) radius, b) mass, c) percentage of metals, d) hydrogen to helium ratio
23. The main sequence lifetime of an O star compared with an M star is
a) much longer because there is more fuel available
b) much shorter because the O star 'burns' fuel at a much faster rate
c) about the same because all stars live about 10 billion years
d) trick question - lifetime depends on other parameters
24. Which of the following cannot be assumed about the stars in a given cluster?
a) they all have nearly the same distance from us
b) they all had the same initial chemical composition
c) they all have the same age
d) they all have the same mass
25. The main sequence turn-off of a cluster of stars is a good indicator of which of the following properties of the cluster?
a) age, b) number of stars in the cluster, c) chemical composition, d) distance
26. Carbon, hydrogen, and helium can all be used as fuels during the career of a massive star. Which of the following gives these elements in the correct order in which they will be consumed in the star?
a) hydrogen, helium, carbon, b) helium, carbon, hydrogen
c) carbon, hydrogen, helium, d) hydrogen, carbon, helium
27. As soon as its core hydrogen is exhausted, a star like the Sun begins to evolve
a) toward the red giant stage, b) toward the zero age main sequence stage
c) up the main sequence to become an O star, d) to become a binary star system
28. When a superwind strips away the outer layers of a star, the resulting shell of expanding gas becomes visible as
a) a planetary nebula, b) an HII region, c) a reflection nebula, d) a dark nebula
29. A planetary nebula is produced by
a) a supernova explosion
b) the dust left over when a cluster of stars forms
c) the gradual loss of its outer layers by a dying star
d) a nova explosion
30. Elements heavier than iron are produced
a) in stars during hydrogen burning
b) in interstellar space
c) during supernova outbursts
d) during carbon burning in massive stars
31. What type of star is supported by the pressure produced by its degenerate electrons?
a) a white dwarf. b) a neutron star, c) a main sequence star, d) a pulsar
32. Which of the following objects can rotate a thousand times per second without being torn apart?
a) white dwarf, b) main sequence star, c) red giant, d) neutron star
33. A pulsar spins rapidly because
a) it conserved angular momentum when it shrank
b) it has been struck a glancing blow by another star
c) it has formed from a very rapidly rotating gas cloud
d) it has been accelerated by explosions on its surface
34. Which of the following is an essential part of Einstein's explanation of gravity?
a) matter causes curvature of space
b) the gravity of a moving object varies with time
c) gravitational forces exist only over a limited distance
d) anti-matter has negative gravity
35. What happens to the light from a star which has contracted within its event horizon?
a) it cannot escape from the region around the star
b) it begins to travel faster than the speed of light
c) it has a strong blue shift
d) there is no longer any relationship between wavelength and energy
36. If the Sun were replaced by a black hole having a mass of one solar mass, what would happen to the Earth's orbit?
a) the Earth would spiral inward
b) the Earth would jump to a smaller orbit
c) the size of the Earth's orbit would increase rapidly
d) the Earth's orbit would remain the same
37. The bright star (not counting the Sun) seen by Chinese astronomers during daylight in the year 1054 AD was
a) the first appearance of Comet Halley
b) the Crab supernova
c) the formation of a massive black hole in the galactic center
d) Alpha centauri reaching the main sequence
38. A star which is discovered to be a binary system on the basis of the Doppler shifts of the spectral lines of its two stars is called a
a) spectroscopic binary, b) astrometric binary, c) visual binary, d) eclipsing binary
39. A light curve is a plot showing
a) luminosity versus spectral type, b) brightness versus time
c) radial velocity versus magnitude, d) mass versus luminosity
40. Which type of binary star is revealed by periodic decreases in brightness?
a) spectroscopic binaries, b) eclipsing binaries
c) visual binaries, d) astrometric binaries
41. (10 points) Explain (with drawings if necessary) what a recurrent nova is and how it works.
42. (10 points) Starting with the main sequence, explain the evolutionary chain of events our Sun will undergo until it is no longer visible to the rest of the universe.