Question 1

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 brighter

Question 2

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.

Question 3

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 Earth

Question 4

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)  8.84

Question 5

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.

Question 6

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.

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 luminosity

Question 7

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.

Question 8

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

Accepted Answer

A)  10 
B)  100 
C)  1000 
D)  10,000

Question 9

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 area

Question 10

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.

Question 11

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.

Question 12

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 brighter

Question 13

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.

Question 14

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 au

Question 15

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 space

Question 16

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 period

Question 17

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.

Question 18

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)  A8

Question 19

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.

Question 20

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.

Exam 12: Characterizing Stars