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PH109 Exploring the Universe Test 3, Fall 2003
Please indicate the best answer to the following question on the answer sheet provided.
1. Of all the stars that are currently on the main sequence, which spectral type would be least abundant?
a. A, b. B, c. K, d. M
2. What mechanism is responsible for the twisting of the Sun's magnetic filed lines?
a. differential rotation, b. convection, c. proton-proton cycle, d. tidal forces
3. Synchrotron radiation is produced by
a. objects with temperature below 10,000 K.
b. high-velocity electrons moving through a magnetic field.
c. cold hydrogen atoms in space.
d. the collapsing cores of massive stars.
4. 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
5. A neutron star is expected to spin rapidly because
a. they conserved angular momentum when they collapsed.
b. they have high orbital velocities.
c. they have high densities.
d. they have high temperatures.
6. What is the correct sequence of spectral types of stars according to temperature
a) OBAFGKM, b) OFGBGMA, c) FABOGKM, d) ABFGKMO
7. What is the single most important characteristic in determining the course of a star's evolution?
a) Absolute brightness., b) Distance., c) Surface temperature., d) Mass.
8. Sunspots appear dark because
a) they are cooler regions, b) they are concentrations of carbon,
c) their spectrum has been Doppler shifted, d) impurities in the Sun
9. When the electron and proton go from aligned spins to opposite spins in the Hydrogen atom. What happens?
a) nuclear fusion, b) nuclear fission, c) 21 cm radiation, d) E=MC 2
10. A star which is discovered to be a binary system on the basis of the Doppler shifts of the spectral
of its two stars is called a
(a) spectroscopic binary, (b) astrometric binary, (c) visual binary, (d) eclipsing binary
11. The fact that convection is occurring in the outer layers of the Sun is demonstrated by
a. solar eruptions, b. sunspots, c. granules, d. solar wind
12. What is the approximate age of the star cluster in the diagram below?
a. 2 million years, b. 2 billion years, c. 10 billion years, d. 100 billion years
e. The age of the cluster can not be estimated from an HR diagram of the cluster
lines
13. 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
14. 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
15. The centers of granules
a. are hot material rising to the photosphere from below.
b. are cool material falling from the photosphere to the regions below.
c. are fainter and hotter than their surroundings.
d. are brighter and cooler than their surroundings.
e. show strong Zeeman effects.
16. A star's luminosity depends only on the star's
a. distance and diameter,
b. temperature and distance,
d. temperature and diameter, e. apparent magnitude.
c. distance.
17. We know that giant stars are larger in diameter than the sun because
a. they are more luminous but have about the same temperature.
b. they are less luminous but have about the same temperature.
c. they are hotter but have about the same luminosity.
d. they are cooler but have about the same luminosity.
e. they have a larger absolute magnitude than the sun.
18. Stars on the main sequence with the greatest mass
a. are spectral type M stars.
b. are spectral type O stars.
c. are located at the bottom of the main sequence in the HR diagram.
d. have masses very similar to the sun.
19. The main sequence has a limit at the lower end because
a. low mass stars form from the interstellar medium very rarely.
b. low mass objects are composed primarily of solids, not gases.
c. pressure does not depend on temperature in degenerate matter.
d. there is a minimum temperature for hydrogen fusion.
20. Which of the following nuclear fuels does a one solar mass star use over the course of its entire evolution?
a. hydrogen, b. hydrogen and helium, c. hydrogen, helium and carbon
d. hydrogen, helium, carbon, and neon, e. hydrogen, helium, carbon, neon, and oxygen.
21. A planetary nebula is
a. the expelled outer envelope of a medium mass star.
b. produced by a supernova explosion.
c. produced by a nova explosion.
d. a nebula within which planets are forming.
e. a cloud of hot gas surrounding a planet.
22. Massive stars cannot generate energy through iron fusion because
a. iron fusion requires very high density.
b. stars contain very little iron.
c. no star can get hot enough for iron fusion.
d. iron is the most tightly bound of all nuclei.
e. massive stars supernova before they create an iron core.
23. Synchrotron radiation is produced by
a. objects with temperature below 10,000 K.
b. high-velocity electrons moving through a magnetic field.
c. cold hydrogen atoms in space.
d. the collapsing cores of massive stars.
24. When material expanding away from a star in a binary system reaches the Roche surface
a. the material will start to fall back toward the star.
b. all of the material will accrete on to the companion.
c. the material is no longer gravitationally bound to the system.
d. the material will increase in temperature an eventually undergo thermonuclear fusion.
25. Pulsars cannot be spinning white dwarfs because
a. white dwarfs are not that common.
b. white dwarfs are not dense enough.
c. white dwarfs do not have magnetic fields.
d. a white dwarf spinning that fast would fly apart
26. The primary reason for the 22 year sunspot cycle is
a. Orbit of Jupiter, b. Alignment of the planets every 22 years.
c. magnetic field reversal d. enhanced synchrotron radiation
27. Sunspots usually occur
a. as single regions, b. in pairs,
c. in groups of three or more, d. as continuous regions around the sun's equator
28. Which element is the Sun currently fusing
a. Hydrogen, b. Helium, c. Carbon, d. Oxygen
29. What will be the last element that the Sun will be able to "burn"
a. Hydrogen, b. Helium, c. Carbon, d. Oxygen
30. A plot of the continuous spectra of five different stars are shown in the figure below. Based on these spectra,
which of the stars is the hottest?
a. Star A, b. Star B, c. Star C, d. Star D, e. Star E
31. The total mass of a binary system can be calculated from
a. the ratio of the angular separation from the center of mass of each of the stars.
b. the distance to the binary and its radial velocity.
c. the semi major axis and period of the orbit.
d. the radial velocities of the two stars.
e. the time required for the small star to eclipse the larger star.
32. Red stars are _____ than blue stars
a. hotter b. cooler c. larger d. smaller
33. When stars evolve they
a. move up the main sequence b. move off the main sequence c. stay the same d. explode
34. What will be the end result of a star like our Sun.
a. white dwarf b. neutron star c. pulsar d. black hole
35. About how old is our Sun?
a. 10 million years b. 5 billion years c. 10 billion years d. 1 million years
36. Why do stars explode?
a. their cores collapse b. nuclear fusion takes place c. starquakes d. E=MC 2
37. Why do neutron stars spin so fast?
a. neutrons move faster than protons b. neutrons are more massive than protons
c. conservation of angular momentum d. they are left over from an explosion
38. Which spectral type of star has not yet lived long enough to have evolved?
a. O b. B c. M d. G
39. How do astronomers determine the mass of stars?
a. by their color, b. by their brightness, c. in binary systems, d. by computer modeling
40. What is the main way astronomers discover black holes?
a. they see them in front of other stars, b. their black body curve is blue shifted,
c. they are in binary systems, d. they are not on the main sequence.