Deck 11: Surveying the Stars

Question 1

The spectral sequence, in order of decreasing temperature, is

A) OFBAGKM.
B) OBAGFKM.
C) OBAFGKM.
D) ABFGKMO.
E) BAGFKMO.

Answer 1

C

Question 2

Which of the following correctly states the relationship between the apparent brightness, luminosity, and distance of a star?

A) luminosity =
B) apparent brightness =
C) apparent brightness = luminosity × 4π × (distance) ²
D) distance =

Answer 2

B

Question 3

Which o the following stars are brightest at ultraviolet wavelengths?

A) O and B stars
B) A and F stars
C) G and K stars
D) M stars
E) none, all stars are brightest at optical wavelengths

Answer 3

A

Question 4

On a Hertzsprung-Russell diagram, where would you find stars that are cool and dim?

A) upper right
B) lower right
C) upper left
D) lower left

Question 5

What are the standard units for apparent brightness?

A) Watts
B) Joules
C) Newtons
D) Watts per second
E) Watts per square meter

Question 6

You see two main-sequence stars with the same spectral type. Star 1 is dimmer in apparent brightness than Star 2 by a factor of 100. What can you conclude, assuming there is no absorption of either star's light by interstellar gas or dust?

A) Without first knowing the distances to these stars, you cannot draw any conclusions about how their true luminosities compare to each other.
B) The luminosity of Star 1 is a factor of 100 less than the luminosity of Star 2.
C) Star 1 is 100 times more distant than Star 2.
D) Star 1 is 100 times nearer than Star 2.
E) Star 1 is 10 times more distant than Star 2.

Question 7

Which of the following statements about apparent and absolute magnitudes is true?

A) The magnitude system that we use now is based on a system used by the ancient Greeks over 2,000 years ago that classified stars by how bright they appeared.
B) A star with an apparent magnitude of 1 appears brighter than a star with an apparent magnitude of 2.
C) The absolute magnitude of a star is another measure of its luminosity.
D) A star's absolute magnitude is the apparent magnitude it would have if it were at a distance of 10 parsecs from Earth.
E) All of the above are true.

Question 8

You measure the parallax angle for a star to be 0.5 arcseconds. The distance to this star is

A) 0.5 light-year.
B) 0.5 parsec.
C) 5 light-years.
D) 5 parsecs.
E) 2 parsecs.

Question 9

What are the standard units for luminosity?

A) Watts
B) Joules
C) Newtons
D) kilograms
E) Watts per second

Question 10

Which of the following statements about spectral types of stars is true?

A) The spectral type of a star can be used to determine its surface temperature.
B) The spectral type of a star can be used to determine its color.
C) A star with spectral type A is cooler than a star with spectral type B.
D) A star with spectral type F2 is hotter than a star with spectral type F3.
E) All of the above are true.

Question 11

A star's luminosity is the

A) apparent brightness of the star in our sky.
B) surface temperature of the star.
C) lifetime of the star.
D) total amount of energy that the star will radiate over its entire lifetime.
E) total amount of energy that the star radiates each second.

Question 12

The spectral sequence sorts stars according to

A) mass.
B) surface temperature.
C) luminosity.
D) core temperature.
E) radius.

Question 13

Which stellar spectral type has strong molecular absorption lines in its optical spectrum?

A) O
B) B
C) G
D) K
E) M

Question 14

The most distant stars we can measure stellar parallax for are approximately

A) 5 parsecs away.
B) 100 parsecs away.
C) 10,000 parsecs away.
D) halfway across the Milky Way Galaxy.
E) in the Andromeda Galaxy.

Question 15

You measure the parallax angle for a star to be 0.1 arcseconds. The distance to this star is

A) 10 light-years.
B) 10 parsecs.
C) 0.1 light-year.
D) 0.1 parsec.
E) impossible to determine.

Question 16

Since all stars begin their lives with the same basic composition, what characteristic most determines how they will differ?

A) location where they are formed
B) time they are formed
C) luminosity they are formed with
D) mass they are formed with
E) color they are formed with

Question 17

Which of the following terms is given to a pair of stars that appear to change position in the sky, indicating that they are orbiting one another?

A) visual binary
B) eclipsing binary
C) spectroscopic binary
D) double star
E) none of the above

Question 18

Which of the following best describes the axes of a Hertzsprung-Russell (H-R) diagram?

A) surface temperature on the horizontal axis and luminosity on the vertical axis
B) mass on the horizontal axis and luminosity on the vertical axis
C) surface temperature on the horizontal axis and radius on the vertical axis
D) mass on the horizontal axis and stellar age on the vertical axis
E) interior temperature on the horizontal axis and mass on the vertical axis

Question 19

If the distance between us and a star is doubled, with everything else remaining the same, its luminosity

A) is decreased by a factor of four, and its apparent brightness is decreased by a factor of four.
B) is decreased by a factor of two, and its apparent brightness is decreased by a factor of two.
C) remains the same, but its apparent brightness is decreased by a factor of two.
D) remains the same, but its apparent brightness is decreased by a factor of four.
E) is decreased by a factor of four, but its apparent brightness remains the same.

Question 20

The faintest star visible to the naked eye has an apparent magnitude of about

A) 10.
B) 6.
C) 1.
D) 0.
E) 6.

Question 21

A star of spectral type G lives approximately how long on the main sequence?

A) 1,000 years
B) 10,000 years
C) 10 million years
D) 1 billion years
E) 10 billion years

Question 22

Which of the following is the most numerous type of main-sequence star?

A) an O star
B) an A star
C) an F star
D) a G star
E) an M star

Question 23

You observe a star cluster with a main-sequence turn-off point at spectral type G2 (the same spectral type as the Sun). What is the age of this star cluster?

A) 10,000 years.
B) 4.6 billion years.
C) 10 billion years.
D) 100 billion years.
E) You also need to know the luminosity class of the turn-off point to determine the age.

Question 24

On a Hertzsprung-Russell diagram, where would you find stars that have the largest radii?

A) upper right
B) lower right
C) upper left
D) lower left

Question 25

On a Hertzsprung-Russell diagram, where would you find white dwarfs?

A) upper right
B) lower right
C) upper left
D) lower left

Question 26

The more distant a star, the smaller its parallax.

Question 27

The age of stars in a cluster can be determined by

A) fitting the position of the main sequence to the Sun.
B) determining the main sequence turnoff point.
C) finding pulsating variable stars in the cluster.
D) finding spectroscopic binaries in the cluster.
E) counting the number of stars in each spectral class.

Question 28

On a Hertzsprung-Russell diagram, where would you find red giant stars?

A) upper right
B) lower right
C) upper left
D) lower left

Question 29

On the main sequence, stars obtain their energy

A) from chemical reactions.
B) from gravitational contraction.
C) by converting hydrogen to helium.
D) by converting helium to carbon, nitrogen, and oxygen.
E) from nuclear fission.

Question 30

Which of the following stellar properties has the greatest range in values?

A) mass
B) radius
C) core temperature
D) surface temperature
E) luminosity

Question 31

A star of spectral type B with a mass of 10 times the mass of the Sun lives approximately how long on the main sequence?

A) 1,000 years
B) 10,000 years
C) 10 million years
D) 1 billion years
E) 10 billion years

Question 32

The apparent brightness of a star depends only on its luminosity.

Question 33

If the distance between us and a star is doubled, its apparent brightness will decrease by a factor of four.

Question 34

On a Hertzsprung-Russell diagram, where would you find stars that are cool and luminous?

A) upper right
B) lower right
C) upper left
D) lower left

Question 35

On a Hertzsprung-Russell diagram, where on the main sequence would you find stars that have the greatest mass?

A) upper right
B) lower right
C) upper left
D) lower left

Question 36

Which of the following statements about globular clusters is true?

A) All stars in the cluster are approximately at the same stage in their evolution.
B) Most of the stars in the cluster are younger than 10 billion years.
C) Most stars in the cluster are yellow or reddish in color.
D) All stars in the cluster have approximately the same mass.
E) There is an approximately equal number of all types of stars in the cluster.

Question 37

Which of the following luminosity classes refers to stars on the main sequence?

A) I
B) II
C) III
D) IV
E) V

Question 38

We can measure the parallax of most stars in our galaxy.

Question 39

Which of the following comparisons between low-mass stars and high-mass stars is true?

A) Low-mass stars are cooler and less luminous than high-mass stars.
B) Low-mass stars are hotter and more luminous than high-mass stars.
C) Low-mass stars are cooler but more luminous than high-mass stars.
D) Low-mass stars are hotter but less luminous than high-mass stars.
E) Low-mass stars have the same temperature and luminosity as high-mass stars.

Question 40

Which of the following statements about open clusters is true?

A) All stars in the cluster are approximately the same color.
B) All stars in the cluster are approximately the same age.
C) All stars in the cluster have approximately the same mass.
D) All stars in the cluster will evolve similarly.
E) There is an approximately equal number of all types of stars in the cluster.

Question 41

The Earth is about 150 million km from the Sun, and the apparent brightness of the Sun in our sky is about 1,300 watts per square meter. Determine the apparent brightness we would measure for the Sun if we were located five times the earth's distance from the Sun.

Question 42

Two stars have the same spectral type. Star X is in luminosity class III, while Star Y is in luminosity class V. Star X must be larger in radius than Star Y.

Question 43

We can measure the radii of stars in eclipsing binary systems.

Question 44

Two stars have the same luminosity. Star X is spectral type F, while Star Y is spectral type K. Star X must be larger in radius than Star Y.

Question 45

The Earth is about 150 million km from the Sun, and the apparent brightness of the Sun in our sky is about 1,300 watts per square meter. Determine the apparent brightness we would measure for the Sun if we were located one-third of the earth's distance from the Sun.

Question 46

Observing Stellar Evolution: Stars evolve on timescales of millions to billions of years, making it impossible for astronomers to follow the life-cycle of any individual star. Explain how astronomers overcome this limitation. Be sure to discuss the important role that observations of star clusters play in revealing the evolution of stars.

Question 47

The faintest visible stars to the naked eye have an apparent magnitude of about 6

Question 48

It is impossible for a star to have a negative apparent magnitude, such as -1.

Question 49

Confusing Terminology in Science: Scientists' love of jargon and acronyms often confounds the public and makes it impossible for them to read scientific literature. Use the example of spectral types introduced in this chapter (i.e. the Sun is a "G2" star) as a case study in jargon. What is the historical origin of the spectral types? Why are the letters in a confusing, non-alphabetical order? Why do you think astronomers persist in using spectral types? Do you think astronomers should drop this notation, and, if so, what should replace it?

Question 50

A star with an apparent magnitude of 10 appears fainter than a star with an apparent magnitude of 9.

Question 51

Two stars both lie on the main sequence. Star X is spectral type A, while Star Y is spectral type G. Star X must be more massive than Star Y.

Question 52

Some stars are cool enough to have molecules in their atmosphere.

Question 53

All stars spend approximately the same amount of time on the main sequence.

Question 54

The size of the Earth's orbit is doubled. This will allow the parallaxes of more distant stars to be measured.

Question 55

The Earth is about 150 million km from the Sun, and the apparent brightness of the Sun in our sky is about 1,300 watts per square meter. Determine the apparent brightness we would measure for the Sun if we were located half the earth's distance from the Sun.

Question 56

Spectral type, surface temperature, and color all describe the same basic characteristic of a star.

Question 57

Blue stars are always more luminous than red stars

Question 58

Our Sun, An Average Star: Often in science it is helpful to talk about a representative example of the objects or phenomena being studied. However, you must always keep in mind that the average case is not always representative. For example, our Sun is often described as an "average" star in the Milky Way. In what sense is this statement true? In what sense is this statement seriously misleading? Do you think it is useful to characterize the stars in the Milky Way by simply citing our "average" Sun?

Question 59

A 10 solar mass star is about ten times more luminous than a 1 solar mass star.

Question 60

Most stars on the main sequence fuse hydrogen into helium in their cores, but some do not.

Question 61

Two stars, Fred and Barney, are of the same size. Fred has spectral type F, while Barney has spectral type B. Which one is more luminous?

Question 62

Which cluster is 10 billion years old?

Question 63

Which group includes the Sun?

Question 64

Which group represents stars that are hot but dim?

Question 65

Which group represents stars that are hot and very bright?

Question 66

Which of the following stars has a spectrum that peaks at the highest frequency?

A) A yellow star
B) A red star
C) A blue star

Question 67

Which group includes stars that are burning elements besides hydrogen in their cores?

Question 68

Which group represents hydrogen-burning stars with the shortest lifetimes?

Question 69

Two stars, Betty and Wilma, are both on the main sequence. Betty is more luminous than Wilma. Which one has a hotter surface temperature? Which one is more massive? Which one is bigger? If they both formed at the same time, which one will evolve off the main sequence first?

Question 70

Which group includes stars that are burning helium in their cores?

Question 71

Which star cluster is the youngest star cluster? The one where the brightest main sequence stars are . . .

A) O stars.
B) A stars.
C) G stars.
D) M stars.
E) B stars.

Question 72

Two stars, Tom and Jerry, have the same spectral type. Tom is luminosity class V and Jerry is luminosity class I. Which star is bigger? Which star is more luminous? Which star has a hotter surface temperature? Explain your answers.

Question 73

Which star is the hottest star?

A) G
B) A
C) O
D) M
E) Can't tell from information provided.

Question 74

Explain why stars more massive than the Sun live shorter main sequence lives than stars less massive than the Sun, despite having more fuel available for nuclear reactions.

Question 75

Explain why stars displaying spectral lines of molecules must be relatively cool.

Question 76

Which is brighter in our sky, a star with apparent magnitude 2 or a star with apparent magnitude 7?

Question 77

Which group represents stars of the smallest radii?

Question 78

A scientist claims that all red main sequence stars are 1 billion years old. Which of the following, if true, would prove that this claim is false?

A) The discovery of a red main sequence star in a star cluster where all the other stars are red giants or red supergiants.
B) Stellar evolution theory predicts that the main sequence lifetime of red stars can be as long as 100 billion years.
C) The minimum lifespan of a red main sequence star is estimated to be 10 billion years.
D) The discovery of a red main sequence star in a star cluster where the main sequence turnoff is about that of the Sun.

Question 79

Which cluster is the youngest?

Question 80

Which cluster is the oldest?