Test Bank for Astronomy The Universe at a Glance 1st
Edition Chaisson McMillan 0321799763 9780321799760
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Astronomy: The Universe at a Glance (Chaisson/McMillan)
Chapter 9 Measuring the Stars
1) The nearest naked- eye star to our Sun, Alpha Centauri, is still over a parsec distant.
Answer: TRUE
Diff: 1
Section Ref: 9.1
2) The proper motion of a star is its true velocity through space.
Answer: FALSE
Diff: 1
Section Ref: 9.1
3) The proper motion of a star, its distance, and Doppler shift can give us its space velocity.
Answer: TRUE
Diff: 2
Section Ref: 9.1
4) First magnitude Spica appears 2.5 times brighter than second magnitude Polaris.
Answer: TRUE
Diff: 2
Section Ref: 9.2
5) Star A and star B have the same apparent magnitude. Star A is twice as distant as star B. Therefore, star A has twice the luminosity as star B.
Answer: FALSE
Diff: 3
Section Ref: 9.2
6) If a star were moved 10 times farther away, its absolute magnitude would drop five magnitudes.
Answer: FALSE
Diff: 3
Section Ref: 9.2
7) If a star were moved 10 times farther away, its apparent magnitude would drop by five magnitudes.
Answer: TRUE
Diff: 3
Section Ref: 9.2
8) A type B9 star is hotter than a type A0.
Answer: TRUE
Diff: 1
Section Ref: 9.3
9) Hydrogen lines are weaker in both very hot and very cool stars.
Answer: TRUE
Diff: 2
Section Ref: 9.3
10) A star of the Sun's diameter, but twice as hot, must be 16X more luminous than the Sun.
Answer: TRUE
Diff: 3
Section Ref: 9.4
11) On the main sequence, almost all stars have radii between about 0.1 and 10 times the Sun.
Answer: TRUE
Diff: 3
Section Ref: 9.5
12) The vast majority of stars near us would fall to the bottom right on the H-R diagram.
Answer: TRUE
Diff: 3
Section Ref: 9.5
13) For luminosity classification, fat stars have skinny spectral lines.
Answer: TRUE
Diff: 1
Section Ref: 9.6
14) In a spectroscopic binary, the star whose lines shift the most weighs the most.
Answer: FALSE
Diff: 1
Section Ref: 9.7
15) Eclipsing binaries are the most useful, giving us sizes as well as masses of the pair.
Answer: TRUE
Diff: 2
Section Ref: 9.7
16) In a binary system, the more massive stars always stay closer to the center of mass and move slower.
Answer: TRUE
Diff: 2
Section Ref: 9.7
17) A nearby star has a parallax of 0.2 arc seconds. What is its distance?
A) .1 parsec
B) .2 parsec
C) .5 parsec
D) 5 parsecs
E) 50 parsecs
Answer: D
Diff: 2
Section Ref: 9.1
18) What is proper motion?
A) It is the true, not apparent, motion of a star in space.
B) It is the apparent shift as we go to opposite sides of our orbit every six months.
C) It is the annual apparent motion of a star across the sky.
D) It is the motion of a star towards or away from us, revealed by Doppler shifts.
E) It is the orbital motion of a star around the Galaxy.
Answer: C
Diff: 1
Section Ref: 9.1
19) Which statement about stellar motion is incorrect?
A) In general, the closer a star is, the more its proper motion.
B) The radial velocity is measured by the Doppler shift.
C) The transverse velocity is measured by the proper motion and the distance.
D) Like parallax, proper motion is measured over intervals of exactly six months.
E) The Pythagorean theorem relates space, transverse, and radial velocities.
Answer: D
Diff: 2
Section Ref: 9.1
20) Which of the following best describes the size and distance relationship of our Sun and the nearest star?
A) A tennis ball here, another on the Moon
B) Two beach balls separated by 100 city blocks
C) Two grains of sand separated by 100 light-years
D) Two golf balls separated by 300 kilometers
E) Two baseballs separated by 100 yards
Answer: D
Diff: 2
Section Ref: 9.1
21) If a star has a parallax of 0.05", then its distance in light-years is about
A) 6.4 light-years.
B) 12.7 light-years.
C) 20 light-years.
D) 65 light-years.
E) 100 light-years.
Answer: D
Diff: 2
Section Ref: 9.1
22) If a star is found by spectroscopic observations to be about 500 parsecs distant, its parallax is
A) .2".
B) .5".
C) .02".
D) .002".
E) .005".
Answer: D
Diff: 2
Section Ref: 9.1
23) Procyon lies about 13 light-years distant, thus its parallax is about
A) 0.01".
B) 0.25".
C) 0.40".
D) 0.65".
E) 1.3".
Answer: B
Diff: 3
Section Ref: 9.1
24) In order to turn a star's proper motion into its space velocity, we must also know
A) its mass and spectral type.
B) its temperature and age.
C) its distance and radial velocity.
D) its distance and mass.
E) its spectral type and period of rotation.
Answer: C
Diff: 3
Section Ref: 9.1
Copyright © 2016 Pearson Education, Inc.
25) If a star appears to move back and forth relative to other stars over a six-month period, this motion is due to the star's
A) transverse motion.
B) radial motion.
C) parallax shift.
D) Doppler shift.
E) true space motion.
Answer: C
Diff: 3
Section Ref: 9.1
26) If a star appears to move relative to other stars over a one-year period, this motion is due to the star's
A) transverse motion.
B) radial motion.
C) parallax shift.
D) Doppler shift.
E) true space motion.
Answer: E
Diff: 3
Section Ref: 9.1
27) Roughly how many stars are within 4 parsecs of the solar system?
A) 3
B) 30
C) 3000
D) 300,000
E) 200 billion
Answer: B
Diff: 1
Section Ref: 9.1
28) What is the absolute magnitude of our Sun?
A) -23.0
B) -4.6
C) -1.4
D) +4.8
E) +9.4
Answer: D
Diff: 2
Section Ref: 9.2
29) The absolute magnitude of a star is its brightness as seen from a distance of
A) one million kilometers.
B) one astronomical unit.
C) one light-year.
D) ten parsecs.
E) 10 light-years.
Answer: D
Diff: 2
Section Ref: 9.2
30) Perhaps the greatest of the Greek astronomers, ________ compiled the first catalog of stars, accurately measured their positions, and defined the basic system of stellar brightnesses.
A) Erastothenes
B) Aristotle
C) Ptolemy
D) Hipparchus
E) Aristarchus
Answer: D
Diff: 2
Section Ref: 9.2
31) In comparing first magnitude Deneb with second magnitude Polaris, we find that
A) Polaris is in reality much more luminous.
B) Deneb must be much hotter than Polaris.
C) Deneb appears 2.5 times brighter to us than does Polaris.
D) Polaris is really 100 times brighter than nearby Deneb.
E) Deneb is really much closer than Polaris.
Answer: C
Diff: 2
Section Ref: 9.2
32) At the distance of Jupiter (6 times further away from the Sun than Earth) the amount of sunlight received per square centimeter different by what factor?
A) 6 times less
B) 12 times less
C) 36 times less
D) 6 times more
E) 12 times more
Answer: C
Diff: 3
Section Ref: 9.2
33) Star A and star B both have an apparent magnitude of 4.0, but star A has an absolute magnitude of 1.0 and star B has an absolute magnitude of 7.0. Which statement below is correct?
A) Star A appears brighter than star B, but star B and star A have the same intrinsic brightness.
B) Star B appears brighter than star A, but star B and star A have the same intrinsic brightness.
C) Star A and star B appear to have the same brightness, but star B is intrinsically brighter than star A.
D) Star A and star B appear to have the same brightness, but star A is intrinsically brighter than star B.
E) It is impossible to determine how bright these stars are or appear to be relative to one another, given the information above.
Answer: D
Diff: 3
Section Ref: 9.2
34) Star A and star B both have an apparent magnitude of 7.0, but star A is at a distance of 15 pc and star B is at a distance of 30 pc. Which statement below is correct?
A) Star A appears brighter than star B, but star B and star A have the same intrinsic brightness.
B) Star B appears brighter than star A, but star B and star A have the same intrinsic brightness.
C) Star A and star B appear to have the same brightness, but star B is intrinsically brighter than star A.
D) Star A and star B appear to have the same brightness, but star A is intrinsically brighter than star B.
E) It is impossible to determine how bright these stars are or appear to be relative to one another, given the information above.
Answer: C
Diff: 3
Section Ref: 9.2
35) Star A and star B both have an absolute magnitude of 2.0, but star A is at a distance of 50 pc and star B is at a distance of 20 pc. Which statement below is correct?
A) Star A appears brighter than star B, but star B and star A have the same intrinsic brightness.
B) Star B appears brighter than star A, but star B and star A have the same intrinsic brightness.
C) Star A and star B appear to have the same brightness, but star B is intrinsically brighter than star A.
D) Star A and star B appear to have the same brightness, but star A is intrinsically brighter than star B.
E) It is impossible to determine how bright these stars are or appear to be relative to one another, given the information above.
Answer: B
Diff: 3
Section Ref: 9.2
Copyright © 2016 Pearson Education, Inc.
36) Star A and star B both have an absolute magnitude of 2.0, but star A has an apparent magnitude of 5.0 and star B has an apparent magnitude of 7.0. Which statement below is correct?
A) Star A appears brighter than star B, but star B and star A have the same intrinsic brightness.
B) Star B appears brighter than star A, but star B and star A have the same intrinsic brightness.
C) Star A and star B appear to have the same brightness, but star B is intrinsically brighter than star A.
D) Star A and star B appear to have the same brightness, but star A is intrinsically brighter than star B.
E) It is impossible to determine how bright these stars are or appear to be relative to one another, given the information above.
Answer: A
Diff: 3
Section Ref: 9.2
37) Star A has an absolute magnitude of 2.5 and star B has an apparent magnitude of 2.5, but star A is a main sequence star and star B is a red giant. Which statement below is correct?
A) Star A appears brighter than star B, but star B and star A have the same intrinsic brightness.
B) Star B appears brighter than star A, but star B and star A have the same intrinsic brightness.
C) Star A and star B appear to have the same brightness, but star B is intrinsically brighter than star A.
D) Star A and star B appear to have the same brightness, but star A is intrinsically brighter than star B.
E) It is impossible to determine how bright these stars are or appear to be relative to one another, given the information above.
Answer: E
Diff: 3
Section Ref: 9.2
38) What physical property of a star does the spectral type measure?
A) Density
B) Luminosity
C) Temperature
D) Mass
E) Composition
Answer: C
Diff: 1
Section Ref: 9.3
39) Star A is a main sequence star of spectral type F2 and star B is a white dwarf of spectral type B4. Which statement below is correct?
A) Star A appears brighter than star B.
B) Star B appears brighter than star A.
C) Star A is hotter than star B.
D) Star B is hotter than star A.
E) None of the above can be said about these two stars.
Answer: D
Diff: 3
Section Ref: 9.3
40) Star A is a main sequence star of spectral type G5 and star B is a red giant of spectral type K2. Which statement below is correct?
A) Star A appears brighter than star B.
B) Star B appears brighter than star A.
C) Star A is hotter than star B.
D) Star B is hotter than star A.
E) None of the above can be said about these two stars.
Answer: C
Diff: 3
Section Ref: 9.3
41) Two red stars have surface temperatures of 3000 K, but Star A's luminosity is about 5% of the Sun's and Star B's luminosity is about 32,000 times the luminosity of the Sun. How much bigger is star B than star A?
A) They are the same size.
B) Star B's radius is about 16 times larger than star A's radius.
C) Star B's radius is about 800 times larger than star A's radius.
D) Star B's radius is about 640,000 times larger than star A's radius.
E) This cannot be determined from the information given.
Answer: C
Diff: 3
Section Ref: 9.4
42) Stars that have masses similar to the Sun's, and sizes similar to the Earth are
A) main sequence stars.
B) white dwarfs.
C) red giants.
D) red dwarfs.
E) brown dwarfs.
Answer: B
Diff: 1
Section Ref: 9.4
43) Compared to the size of the Sun, in what range of sizes are nearly all stars found?
A) .5 to 2 solar radii
B) 0.1 to 1.0 solar radii
C) 0.5 to 50 solar radii
D) 1 to 100 solar radii
E) 0.01 to 100 solar radii
Answer: E
Diff: 2
Section Ref: 9.5
44) On the H-R diagram, the Sun lies
A) at the top left.
B) at the bottom left.
C) at the bottom right.
D) about the middle of the main sequence.
E) at the top right.
Answer: D
Diff: 1
Section Ref: 9.5
45) Which of the following is the most common type of star?
A) High mass main sequence
B) Low mass main sequence
C) White dwarfs
D) Red giants
E) Blue supergiants
Answer: B
Diff: 1
Section Ref: 9.5
46) The Hertzsprung-Russell Diagram plots ________ against the spectral type or temperature.
A) distance
B) luminosity or absolute magnitude
C) brightness or apparent magnitude
D) size or density
E) mass
Answer: B
Diff: 1
Section Ref: 9.5
47) How might the most common occurring stars be described, based on our stellar neighborhood?
A) White dwarfs
B) K giants
C) G main sequence
D) A main sequence
E) M main sequence
Answer: E
Diff: 2
Section Ref: 9.5
48) On the H-R diagram, red supergiants like Betelgeuse lie
A) at the bottom left.
B) at the bottom right.
C) at the top left.
D) at the top right.
E) They can't be plotted, for they are not main sequence.
Answer: D
Diff: 2
Section Ref: 9.5
49) On the H-R diagram, white dwarfs lie Sirius B and Procyon B lie
A) at the top left.
B) at the top right.
C) close to the Sun, near the center.
D) at the lower left.
E) at the lower right.
Answer: D
Diff: 2
Section Ref: 9.5
50) In the H-R diagram, the bright blue-white stars that dominate the naked eye sky lie to the
A) top left.
B) top right.
C) middle of the main sequence.
D) top center.
E) bottom left.
Answer: A
Diff: 2
Section Ref: 9.5
51) What are the two most important intrinsic properties used to classify stars?
A) Mass and age
B) Luminosity and surface temperature
C) Distance and luminosity
D) Distance and surface temperature
E) Distance and color
Answer: B
Diff: 1
Section Ref: 9.5
52) Having nothing to do with trigonometry, ________ parallaxes use the width of absorption lines to estimate the star's luminosity and size and distance.
A) bolometric
B) photometric
C) spectroscopic
D) holographic
E) videometric
Answer: C
Diff: 1
Section Ref: 9.6
53) In general, the narrower the spectral line of a star
A) the hotter the star is.
B) the bigger the star is.
C) the denser the star is.
D) the smaller the star is.
E) the cooler the star is.
Answer: B
Diff: 2
Section Ref: 9.6
54) Upon what data do measurements of sizes of eclipsing binaries depend?
A) Their orbital periods and separations
B) Their masses and luminosities
C) Their Doppler shifts and durations of stages of their eclipses
D) Their temperatures and speeds
E) Their temperatures and masses
Answer: C
Diff: 2
Section Ref: 9.7
55) Which type of binary can have their sizes measured directly by photometry?
A) Virtual
B) Visual
C) Eclipsing
D) Spectroscopic
E) Astrometric
Answer: C
Diff: 2
Section Ref: 9.7
56) In what range of masses are most stars found?
A) .1 to 2 solar masses
B) 1 to 3 solar masses
C) .1 to 100 solar masses
D) .01 to 100 solar masses
E) Stars can have any mass.
Answer: C
Diff: 2
Section Ref: 9.7
57) In a visual binary system with circular orbits, if in 20 years the two stars' position angles have shifted by 30 degrees, the pair's period must be
A) 60 years.
B) 90 years.
C) 120 years.
D) 240 years.
E) 360 years.
Answer: D
Diff: 2
Section Ref: 9.7
58) In a spectroscopic binary system, the star showing the larger blue shift is
A) cooler and receding the fastest.
B) less massive of the pair and receding slower.
C) more massive and approaching us.
D) less massive and approaching us at this moment.
E) hotter and receding faster.
Answer: D
Diff: 3
Section Ref: 9.7
59) In a spectroscopic binary, if a pair shows a combined set of lines tonight, but a maximum split two nights later, its orbital period must be
A) one day.
B) two days.
C) four days.
D) eight days.
E) twelve days.
Answer: D
Diff: 3
Section Ref: 9.7
60) A star with a parallax of 1 second of arc is at a distance of ________ by definition.
Answer: one parsec
Diff: 1
Section Ref: 9.1
61) A star's motion across the sky is its ________ motion.
Answer: proper
Diff: 2
Section Ref: 9.1
62) The ________ magnitude of a star depends directly upon its luminosity and distance.
Answer: apparent
Diff: 1
Section Ref: 9.2
63) From hottest to coolest, the seven letters for the star types are ________.
Answer: OBAFGKM
Diff: 1
Section Ref: 9.3
64) If two stars are the same size and one is twice the temperature of the other, how much more luminous is the hotter one?
Answer: 16 times
Diff: 2
Section Ref: 9.4
65) Capella is the same temperature as our Sun, but about ten times the Sun's diameter; it must be about ________ times as luminous as our star.
Answer: 100
Diff: 3
Section Ref: 9.4
66) Knowledge of a star's temperature and ________ enables us to calculate its radius, surface area, and volume from the appropriate radiation law.
Answer: luminosity or absolute magnitude
Diff: 2
Section Ref: 9.4
67) On the H-R diagram, most bright naked eye stars would lie at the ________.
Answer: top left
Diff: 2
Section Ref: 9.5
68) On the main sequence on an H-R diagram, our Sun lies at about ________.
Answer: the center
Diff: 2
Section Ref: 9.5
69) All classes of binary stars yield the basic information on stellar ________.
Answer: masses
Diff: 1
Section Ref: 9.7
70) In an eclipsing binary, the longer the stages of the eclipse take, the ________ the star.
Answer: larger
Diff: 2
Section Ref: 9.7
71) How is proper motion measured?
Answer: It is the apparent motion of the star, in seconds of arc, over an interval of exactly one year, after the Earth returns to the same place in its orbit, and all parallax is negated.
Diff: 2
Section Ref: 9.1
72) Why must both parallax and proper motion be known to give transverse velocity?
Answer: To turn the star's apparent motion across our line of sight into its real velocity in that direction, we also need to know the actual distance from parallax data.
Diff: 2
Section Ref: 9.1
73) The apparent magnitude of the Sun is -26, while Sirius has an apparent magnitude of -1; how much brighter does the Sun appear than Sirius?
Answer: This is a difference of 25 magnitudes. As each 5 magnitudes is a brightness factor of 100X, then 100 to the fifth power is 10 billion times brighter.
Diff: 2
Section Ref: 9.2
74) What role does hydrogen play in spectral classification?
Answer: Its spectral lines are most obvious in mid-temperature stars and least obvious in both very hot and very cool stars.
Diff: 2
Section Ref: 9.3
75) How can a white dwarf be hotter than our Sun, yet much less luminous?
Answer: They are only about as big as Earth, so their surface area is about 10,000X less than the Sun's.
Diff: 2
Section Ref: 9.4
76) Contrast main sequence stars of type B and G.
Answer: The B star will be hotter, larger, more massive and more luminous.
Diff: 2
Section Ref: 9.5
77) Why is the main sequence main? Why are these stars so common?
Answer: While their masses, luminosities, and temperatures vary greatly, like the Sun, all of them are relatively young, with plenty of hydrogen still left to turn into helium in their cores. Hydrogen is still the most common element in the universe.
Diff: 3
Section Ref: 9.5
78) How is distance determined to the nearest stars? How far out can this technique be applied? How many stars can be measured in this way?
Answer: The distance to the nearest stars is measured using parallax. The star is observed when the Earth is on either side of its orbit, six months apart. From the slight motion of the star, resulting from the Earth's change in perspective, and knowing the size of the Earth's orbit, the distance to the star can be calculated. The GAIA mission should be able to measure the distance to billions of stars (10,000 or more parsecs distant).
Diff: 2
Section Ref: 9.1
79) What is proper motion? How is it related to transverse velocity?
Answer: Annual apparent motion of a star across the sky, in arc seconds per year. If we also know the star's distance, this angular motion can be turned into the transverse velocity in km/sec.
Diff: 2
Section Ref: 9.1
80) What types of observations are necessary to determine the motion of a star through space?
Answer: To determine the true space motion of a star both the radial velocity and transverse velocities must be determined. The radial velocity can be determined directly from observing the spectrum and measuring the Doppler shift of the absorption lines. The transverse velocity is calculated from observations of a star's proper motion and distance. The proper motion is the angular motion per year of the star. Once the radial velocity and transverse velocities are known, the space motion of the star is calculated using the Pythagorean theorem (square root of the sum of the squares of the velocities).
Diff: 3
Section Ref: 9.1
81) Two stars have apparent magnitudes of 0 and 5. If both stars are 117 parsecs away, which star is intrinsically brighter and by what factor is it brighter than the other?
Answer: Since both stars are at the same distance (it does not matter what the distance is), the magnitude 0 star is the brightest. It is intrinsically 100 times brighter than the magnitude 5 star because 5 magnitudes is always a factor of 100 in intrinsic brightness.
Diff: 3
Section Ref: 9.2
82) What types of observations are necessary to determine the absolute luminosity of a star?
Answer: The absolute luminosity of a star, or absolute magnitude, is determined from the apparent magnitude and distance. The apparent magnitude is rather easily measured using a telescope and a photometer. The distance can be much harder to determine. If the star is nearby then its parallax can be measured. If more distant, some other method will have to be used, such as spectroscopic parallax. Spectroscopic parallax will give the absolute magnitude of the star without having to compute distance.
Diff: 3
Section Ref: 9.2
83) Why are spectra of stars different?
Answer: Spectra of stars differ primarily because of differences in their temperatures. Smaller differences occur because of luminosity differences and even smaller differences occur because of slightly different compositions.
Diff: 3
Section Ref: 9.3
84) A star similar to Sirius A has a temperature of about 10,000 K, and a luminosity of around 25 times that of the Sun. Approximately what is its radius?
Answer: Using T in units of 5000 K, that gives T=2, L = 25, so R = sqrt(25) / 2 = 2.5 times the radius of the Sun, consistent with the value of 2.8 times the radius of the Sun for Sirius A.
Diff: 3
Section Ref: 9.4
85) In a large sampling of stars, the largest group represented in the H-R diagram will be the main sequence stars. Why are they so common?
Answer: Like the Sun, they are young enough to have most of their initial hydrogen still not fused into helium; they will not evolve off the main sequence until the helium builds up a lot. Since hydrogen is by far the most abundant element and the easiest to fuse, most stars are going to use it as their major fuel, as long as the supply lasts. Stars spend the vast majority of their life spans on the main sequence.
Diff: 2
Section Ref: 9.5
86) Explain how the shifting spectral lines of spectroscopic binaries let us find their periods.
Answer: When aligned in our line of sight, there is no radial velocity, and all lines appear single. A quarter of a period later, one is approaching us with its line blue shifted, and the other is receding. Multiply this time span by four, and the two stars are back in the original positions.
Diff: 2
Section Ref: 9.7