Question 1

Absolute magnitude is defined as the apparent magnitude that a star would have if

Accepted Answer

A)   all the energy from the star were concentrated in the visual region.
B)   it were located at exactly 10 ly from Earth.
C)   it were located at exactly 10 pc from Earth.
D)   it were located at exactly 10 au from Earth.E) A) and B)
F) A) and C)

Question 2

The absolute magnitude of a star is the brightness the star would appear to have if it were placed at what distance from Earth?

Accepted Answer

A)   32.6 ly
B)   distance to the galactic center
C)   10 ly
D)   1 auE) None of the above
F) A) and D)

Question 3

A particular star appears approximately equally bright when viewed through a blue filter and through a yellow filter. What is the approximate surface temperature of this star?

Accepted Answer

A)   6000 K
B)   12,000 K
C)   3000 K
D)   It is not possible for a star to be equally bright at two different wavelengths.E) A) and C)
F) All of the above

Question 4

For MOST stars, the

Accepted Answer

A)   absolute magnitude is a larger number than the apparent magnitude.
B)   apparent magnitude is a larger number than the absolute magnitude.
C)   absolute magnitude and the apparent magnitude are numerically equal.
D)   chances are about even of the apparent magnitude being larger or the absolute magnitude being larger.E) B) and C)
F) A) and C)

Question 5

Which important property of stars can be BEST determined by observations of binary stars systems?

Accepted Answer

A)   stellar mass
B)   surface temperature
C)   distance from Earth
D)   pulsation periodE) A) and B)
F) None of the above

Question 6

In the spectral classification scheme, what designation is given to a star just a little hotter than an F8 star?

Accepted Answer

A)   F7
B)   F9
C)   G8
D)   A8E) B) and D)
F) None of the above

Question 7

If the intrinsically brightest stars in Earth's sky have absolute magnitudes of -10, how bright (in terms of total energy output per second)  are these stars compared with the Sun, whose absolute magnitude is +4.8?

Accepted Answer

A)   about 14.8 times brighter
B)   about 800,000 times brighter
C)   about 8000 times brighter
D)   about 1015, or 1,000,000,000,000,000, times brighterE) A) and B)
F) C) and D)

Question 8

A particular star is at a distance of 20 pc from Earth. For this star, the apparent magnitude will have

Accepted Answer

A)   a larger value than its absolute magnitude.
B)   a smaller value than its absolute magnitude.
C)   the same value as its absolute magnitude, since magnitude is independent of distance.
D)   a larger or a smaller value than the absolute magnitude, depending on the temperature and diameter of the star.E) A) and C)
F) B) and C)

Question 9

How many times brighter than a magnitude +4.0 star is a magnitude +3.0 star?

Accepted Answer

A)   100 times brighter
B)   twice as bright
C)   a factor of 4/3, or 1.333 times, brighter
D)   2.512 times brighterE) B) and D)
F) A) and D)

Question 10

How many eleventh magnitude stars are required to equal the brightness of one first magnitude?

Accepted Answer

A)   10
B)   100
C)   1000
D)   10,000E) C) and D)
F) A) and D)

Question 11

Which of these MOST plausibly explains why the star Bellatrix in Orion looks bluish to the naked eye?

Accepted Answer

A)   The spectrum of light emitted from Bellatrix peaks in the blue region of the spectrum, with almost all its light concentrated in the blue region of the spectrum.
B)   The spectrum of light emitted from Bellatrix peaks in the ultraviolet region of the spectrum. Within the visible part of the spectrum, there is more emission in the blue than in any other color.
C)   Bellatrix is moving toward Earth rapidly enough that its light appears appreciably blueshifted.
D)   Bellatrix is made of blue material.E) B) and D)
F) B) and C)

Question 12

The Hipparcos satellite was able to measure parallax for stars out to about 150 pc. This distance includes roughly 2.5 million stars. What is the average number of stars in 1 cubic parsec?

Accepted Answer

A)   5.1 × 10-3
B)   0.18
C)   5.65
D)   8.84E) B) and D)
F) A) and D)

Question 13

Astronomers originally classified the spectra of stars according to the strengths of their hydrogen lines. What new physical insight enabled a reinterpretation of these patterns in terms of surface temperature during the 1920s?

Accepted Answer

A)   discovery of nuclear physics and how stars generate their energy
B)   discovery of blackbody radiation and the blackbody curve
C)   development of atomic physics and how atoms emit light
D)   development of radio astronomy and the detection of molecules in spaceE) None of the above
F) A) and B)

Question 14

What is a star's luminosity?

Accepted Answer

A)   amount of energy received per second on 1 m2 of a planet's surface exactly 1 au from the star
B)   total energy emitted by the star into all space per second, measured in watts
C)   apparent magnitude the star would have if it were located exactly 10 ly from Earth
D)   apparent magnitude the star would have if it were located exactly 10 pc from EarthE) A) and D)
F) A) and C)

Question 15

Which of these statements can be used to define stellar parallax?

Accepted Answer

A)   Stellar parallax is the angle taken up by the diameter of a star as seen from Earth.
B)   Stellar parallax is the angle subtended by the radius of Earth's orbit as seen from the star.
C)   Stellar parallax is the angle subtended by the diameter of Earth's orbit as seen from the star.
D)   Stellar parallax is the angle through which a star moves in the sky over the course of 1 year due to the motion of both the star and Earth.E) C) and D)
F) B) and C)

Question 16

What will be the intrinsic brightness or luminosity of a white dwarf star that has the same temperature as the Sun? See Figure 12-7 in the text. -2 of the Sun's luminosity D)  10-4 of the Sun's luminosity" class="answers-bank-image d-inline" rel="preload" >

Accepted Answer

A)   4 times the Sun's luminosity
B)   Because it has the same surface temperature, the white dwarf will have the same brightness.
C)   10-2 of the Sun's luminosity
D)   10-4 of the Sun's luminosityE) B) and D)
F) None of the above

Question 17

Why are Balmer absorption lines very weak in the spectra of stars with low surface temperatures-significantly below 10,000 K, for example?

Accepted Answer

A)   The hydrogen atoms have to be hot enough to be ionized in order to show Balmer absorption.
B)   There is no emitted continuum radiation at Balmer-line wavelengths when the gas is so cool, so absorption will not be seen.
C)   Atoms need electrons that have been excited by high temperatures to the n = 2 level to undergo Balmer absorption.
D)   Hydrogen atoms have no electrons in any energy levels at these temperatures.E) A) and D)
F) None of the above

Question 18

What condition is necessary on Earth to see eclipses of stars in binary star systems?

Accepted Answer

A)   The stars must have very similar surface temperatures, whatever the inclination of their orbital plane to the line of sight, to see a significant eclipse.
B)   The line of sight from Earth to the star system must be very close to perpendicular to the orbital plane of the stars.
C)   The line of sight from Earth to the star system must be in or very close to the orbital plane of the stars.
D)   One of the stars must be much bigger than the other so that it can hide its smaller companion when the orbital plane is at a large angle to the line of sight.E) A) and C)
F) None of the above

Question 19

When comparing two stars, the one with the _____ must have the greater luminosity.

Accepted Answer

A)   larger radius
B)   higher surface temperature
C)   smaller absolute magnitude
D)   larger surface areaE) A) and B)
F) A) and C)

Question 20

Suppose the distance between an observer and a lightbulb is doubled. How does its final brightness compare with its initial brightness?

Accepted Answer

A)   The lightbulb appears 1/16 as bright.
B)   The lightbulb appears 4 times brighter.
C)   The lightbulb appears 1/2 as bright.
D)   The lightbulb appears 1/4 as bright.E) C) and D)
F) A) and B)

Exam 12: Characterizing Stars

Suppose the distance between an observer and a lightbulb is doubled. How does its final brightness compare with its initial brightness?

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Which important property of stars can be BEST determined by observations of binary stars systems?

Correct AnswerverifiedShow Answer

Astronomers originally classified the spectra of stars according to the strengths of their hydrogen lines. What new physical insight enabled a reinterpretation of these patterns in terms of surface temperature during the 1920s?

Correct AnswerverifiedShow Answer

When comparing two stars, the one with the _____ must have the greater luminosity.

Correct AnswerverifiedShow Answer

A particular star is at a distance of 20 pc from Earth. For this star, the apparent magnitude will have

Correct AnswerverifiedShow Answer

What condition is necessary on Earth to see eclipses of stars in binary star systems?

Correct AnswerverifiedShow Answer

Why are Balmer absorption lines very weak in the spectra of stars with low surface temperatures-significantly below 10,000 K, for example?

Correct AnswerverifiedShow Answer

The Hipparcos satellite was able to measure parallax for stars out to about 150 pc. This distance includes roughly 2.5 million stars. What is the average number of stars in 1 cubic parsec?

Correct AnswerverifiedShow Answer

For MOST stars, the

Correct AnswerverifiedShow Answer

A particular star appears approximately equally bright when viewed through a blue filter and through a yellow filter. What is the approximate surface temperature of this star?

Correct AnswerverifiedShow Answer

If the intrinsically brightest stars in Earth's sky have absolute magnitudes of -10, how bright (in terms of total energy output per second) are these stars compared with the Sun, whose absolute magnitude is +4.8?

Correct AnswerverifiedShow Answer

How many eleventh magnitude stars are required to equal the brightness of one first magnitude?

Correct AnswerverifiedShow Answer

Absolute magnitude is defined as the apparent magnitude that a star would have if

Correct AnswerverifiedShow Answer

Which of these statements can be used to define stellar parallax?

Correct AnswerverifiedShow Answer

Which of these MOST plausibly explains why the star Bellatrix in Orion looks bluish to the naked eye?

Correct AnswerverifiedShow Answer

The absolute magnitude of a star is the brightness the star would appear to have if it were placed at what distance from Earth?

Correct AnswerverifiedShow Answer

What is a star's luminosity?

Correct AnswerverifiedShow Answer

In the spectral classification scheme, what designation is given to a star just a little hotter than an F8 star?

Correct AnswerverifiedShow Answer

How many times brighter than a magnitude +4.0 star is a magnitude +3.0 star?

Correct AnswerverifiedShow Answer

What will be the intrinsic brightness or luminosity of a white dwarf star that has the same temperature as the Sun? See Figure 12-7 in the text.

Correct AnswerverifiedShow Answer

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