Deck 12: Surveying the Stars

Question 1

The spectral sequence sorts stars according to

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

Answer 1

D

Question 2

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

A)A star with an apparent magnitude of 1 appears brighter than a star with an apparent magnitude of 2.
B)The absolute magnitude of a star is another measure of its luminosity.
C)A star's absolute magnitude is the apparent magnitude it would have if it were at a distance of 10 parsecs from Earth.
D)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.
E)All of the above are true.

Answer 2

E

Question 3

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

Answer 3

D

Question 4

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)color they are formed with
C)luminosity they are formed with
D)time they are formed
E)mass they are formed with

Question 5

The sketch above shows groups of stars on the H- R diagram, labeled (a)through (e); note that (a)represents the entire main sequence while (c)and (d)represent only small parts of the main sequence. Which group represents stars with the longest main- sequence lifetimes?

A)a
B)b
C)c
D)d
E)e

Question 6

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 7

The choices below each describe the appearance of an H- R diagram for a different star cluster. Which cluster is the youngest?

A)The diagram shows no main- sequence stars at all, but it has numerous supergiants and white dwarfs.
B)The diagram shows main- sequence stars of every spectral type except O, along with a few giants and supergiants.
C)The diagram shows main- sequence stars of all the spectral types except O and B, along with a few giants and supergiants.
D)The diagram shows main- sequence stars of spectral types G, K, and M, along with numerous giants and white dwarfs.

Question 8

If Star A is closer to us than Star B, then Star A's parallax angle is _ .

A)smaller than that of Star B
B)larger than that of Star B
C)fewer parsecs than that of Star B
D)hotter than that of Star B

Question 9

The sketch above shows groups of stars on the H- R diagram, labeled (a)through (e); note that (a)represents the entire main sequence while (c)and (d)represent only small parts of the main sequence. Which group represents stars of the largest radii?

A)a
B)b
C)c
D)d
E)e

Question 10

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 11

What is the approximate chemical composition (by mass)with which all stars are born?

A)98% hydrogen, 2% helium
B)95% hydrogen, 4% helium, no more than 1% heavier elements
C)Half hydrogen and half helium
D)Three quarters hydrogen, one quarter helium, no more than 2% heavier elements

Question 12

The sketch above shows groups of stars on the H- R diagram, labeled (a)through (e); note that (a)represents the entire main sequence while (c)and (d)represent only small parts of the main sequence. Which group represents the most common type of stars?

A)e
B)b
C)c
D)d

Question 13

Ten parsecs is about _.

A)150 million kilometers
B)10,000 seconds
C)10 parallax seconds of angle
D)32.6 light- years

Question 14

A star is observed with a surface temperature of 3,000 K and a luminosity of 10-2 solar. What is the approximate radius of this star?

A)1 solar radius
B)0)3 solar radius
C)0)1 solar radius
D)The radius cannot be determined.

Question 15

What are the standard units for apparent brightness?

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

Question 16

Which of the following statements about spectral types of stars is not generally true?

A)The spectral type of a star can be used to determine its distance.
B)The spectral type of a star can be used to determine its color.
C)The spectral type of a star can be used to determine its surface temperature.
D)The spectral type of a star can be determined by identifying lines in its spectrum.

Question 17

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

A)0)1 parsec.
B)10 parsecs.
C)0)1 light- year.
D)10 light- years.
E)impossible to determine.

Question 18

Assuming that we can measure the apparent brightness of a star, what does the inverse square law for light allow us to do?

A)determine both the star's distance and luminosity from its apparent brightness
B)calculate the star's surface temperature if we know either its luminosity or its distance
C)determine the distance to the star from its apparent brightness
D)calculate the star's luminosity if we know its distance, or calculate its distance if we know its luminosity

Question 19

Star X has an apparent magnitude of 3, and star Y has an apparent magnitude of 13. How do they compare in observed brightness?

A)Star Y is 10,000 times brighter than star X.
B)Star Y is 10 times brighter than star X.
C)Star X is 10,000 times brighter than star Y.
D)Star X is 10 times brighter than star Y.

Question 20

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

Question 21

What is the approximate age of a star cluster where the brightest main sequence stars are G stars?

A)10 million years
B)10 billion years
C)100 billion years

Question 22

Which star is the hottest star?

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

Question 23

Which main- sequence star has the lowest mass?

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

Question 24

What is the spectral type of a main sequence star with a luminosity 100 times greater than the sun?

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

Question 25

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

Question 26

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

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

Question 27

An O- star has a hotter surface temperature than the Sun. Therefore, compared to the Sun,

A)it emits at about the same wavelengths as the Sun (similar peak)but it is much fainter.
B)its emission peaks in the infrared part of the spectrum.
C)it emits at about the same wavelengths as the Sun (similar peak)but it is much brighter.
D)its emission peaks in the blue part of the spectrum.

Question 28

Astronomers can measure a star's mass in only certain cases. Which one of the following cases might allow astronomers to measure a star's mass?

A)We know the star's luminosity and distance.
B)The star is of spectral type G.
C)The star is of spectral type A.
D)The star is a member of a binary star system.

Question 29

On an H- R diagram, stellar masses _.

A)are greatest in the lower left and least in the upper right
B)are impossible to determine
C)can be determined for main sequence stars but not for other types of stars
D)decrease from upper left to lower right

Question 30

A star is observed with a surface temperature of 3,000 K and a lumi nosity of 105 solar. What is the approximate radius of this star?

A)103 solar radii
B)10 solar radii
C)102 solar radii
D)The radius cannot be determined.

Question 31

Star A is identical to Star B, except that Star A is twice as far from us as Star B. Therefore, _ .

A)both stars have the same luminosity, but the apparent brightness of Star B is four times that of Star A
B)both stars have the same luminosity, but the apparent brightness of Star A is four times that of Star B
C)both stars have the same luminosity, but the apparent brightness of Star B is twice that of Star A
D)both stars have the same apparent brightness, but the luminosity of Star B is four times that of Star A

Question 32

What can we infer, at least roughly, from a star's luminosity class?

A)its mass
B)its size (radius)
C)its age in years
D)its surface temperature

Question 33

Why do O stars exhibit weak hydrogen absorption lines?

A)At these high temperatures, nearly all the hydrogen is ionized, and is therefore unable to interact with light.
B)O stars contain very little hydrogen.
C)O stars are too cool to excite hydrogen atoms to the first energy level from which they can then absorb visible wavelengths of light.

Question 34

The star Vega has an absolute magnitude of about 4 and an apparent magnitude of about 0. Based on the definitions of absolute and apparent magnitude, we can conclude that .

A)Vega's surface temperature is cooler than the Sun
B)Vega's luminosity is less than that of our Sun
C)Vega has a parallax angle of 1/10 arcsecond
D)Vega is nearer than 10 parsecs from Earth

Question 35

To calculate the masses of stars in a binary system, we must measure their .

A)orbital period and average orbital distance
B)luminosities and distance from Earth
C)absolute magnitudes and luminosities
D)spectral types and distance from Earth

Question 36

What is the approximate surface temperature of a star with weak hydrogen absorption lines and strong absorption lines of ionized calcium?

A)4,500 K
B)6,500 K
C)5,500 K
D)3,500 K

Question 37

From hottest to coolest, the order of the spectral types of stars is .

A)OMKGFBA
B)OBAGFKM
C)ABCDEFG
D)ABFGKMO
E)OBAFGKM

Question 38

The axes on a Hertzsprung- Russell (H- R)diagram represent _ .

A)mass and luminosity
B)mass and radius
C)luminosity and surface temperature
D)luminosity and apparent brightness

Question 39

Star X has an apparent magnitude of 3, and star Y has an apparent magnitude of 8. How do they compare in observed brightness?

A)Star Y is 5 times brighter than star X.
B)Star Y is 100 times brighter than star X.
C)Star X is 5 times brighter than star Y.
D)Star X is 100 times brighter than star Y.

Question 40

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

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

Question 41

The brightest main- sequence star in a cluster has a temperature of 10,000 K and a luminosity about 100 times greater than the sun. What is the approximate age of the cluster?

A)About 107 years
B)About 1011 years
C)About 109 years
D)This cannot be answered using the HR diagram.

Question 42

What do we mean by the main- sequence turnoff point of a star cluster, and what does it tell us?

A)It is the spectral type of the hottest main- sequence star in a star cluster, and it tells us the cluster's age.
B)It is the point in a star cluster beyond which main sequence stars are not found, and it tells us the cluster's distance.
C)It is the mass of the most massive star in the star cluster, and it tells us the cluster's size.
D)It is the luminosity class of the largest star in a star cluster, and it tells us the cluster's age.

Question 43

A stars exhibit strong hydrogen absorption lines because the surface temperature of 10,000 K is high enough to place most hydrogen in an excited, but not yet ionized, state. The transitions from this excited state then correspond to visible light wavelengths. Which of the following statements is a plausible explanation for why G stars exhibit weak hydrogen absorption lines?

A)G stars are too cool to excite hydrogen atoms to the first energy level from which they can then absorb visible wavelengths of light.
B)At these high temperatures, nearly all the hydrogen is ionized, and unable to interact with light.
C)G stars contain very little hydrogen.

Question 44

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

A)1,000 parsecs away.
B)10,000 parsecs away.
C)in the Andromeda Galaxy.
D)halfway across the Milky Way Galaxy.
E)5 parsecs away.

Question 45

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

A)Low- mass stars are hotter and more luminous than high- mass stars.
B)Low- mass stars are cooler and less 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 46

Sirius is a star with spectral type A and Rigel is a star with spectral type B. What can we conclude?

A)Rigel has a higher surface temperature than Sirius.
B)Rigel has a higher core temperature than Sirius.
C)Sirius has a higher surface temperature than Rigel.
D)Sirius has a higher core temperature than Rigel.

Question 47

Which of the following statements about globular clusters is true?

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

Question 48

What is the approximate surface temperature of a B star?

A)40,000 K
B)6,000 K
C)20,000 K
D)8,000 K

Question 49

Which of the following statements comparing open and globular star clusters is not true?

A)Stars in open clusters are relatively young while stars in globular clusters are very old.
B)Open and globular clusters each typically contain a few hundred stars.
C)For both open and globular clusters, we can assume that all the stars in a particular cluster are about the same age.
D)Open clusters are found only in the disk of the galaxy while globular clusters may be found both in the disk and the halo of the galaxy.

Question 50

A star's luminosity is the

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

Question 51

Which main- sequence star will have the shortest lifetime?

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

Question 52

Each choice below lists a spectral type and luminosity class for a star. Which one is a red supergiant?

A)spectral type M2, luminosity class I
B)spectral type O9, luminosity class I
C)spectral type M1, luminosity class V
D)spectral type G2, luminosity class V

Question 53

What is the common trait of all main- sequence stars?

A)They are in the final stage of their lives.
B)They are all spectral type G.
C)They generate energy through hydrogen fusion in their core.
D)They all have approximately the same mass.

Question 54

On an H- R diagram, stellar radii .

A)are greatest in the lower left and least in the upper right
B)decrease from left to right
C)are impossible to determine
D)increase diagonally from the lower left to the upper right

Question 55

What is the approximate luminosity of a main- sequence star with weak hydrogen absorption lines and strong absorption lines of ionized calcium?

A)About 10-2 solar
B)About 0.1 solar
C)About 3 solar
D)About 1 solar

Question 56

Suppose our Sun were suddenly replaced by a supergiant star. Which of the following would be true?

A)The supergiant would appear as large as the full Moon in our sky.
B)Earth would be inside the supergiant.
C)Earth would fly off into interstellar space.
D)The supergiant's surface temperature would be much hotter than the surface temperature of our Sun.

Question 57

The age of stars in a cluster can be determined by

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

Question 58

Careful measurements reveal that a star maintains a steady apparent brightness at most times, except that at precise intervals of 73 hours the star becomes dimmer for about 2 hours. The change in brightness alternates between a small change and a large change. The most likely explanation is that .

A)the star is a white dwarf
B)the star is periodically ejecting gas into space, every 73 hours
C)the star is a member of an eclipsing binary star system
D)the star is a Cepheid variable

Question 59

On the main sequence, stars obtain their energy

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

Question 60

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

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

Question 61

If a star has a mass of 10 solar masses and a luminosity of 10,000 solar luminosities, how long is its lifetime? (The Sun's lifetime is 10 billion years.)

A)100 billion years
B)100 trillion years
C)1 million years
D)10 million years

Question 62

Two separate pairs of binary stars are observed. The separation of the pairs is identical, but the orbital period of Pair X is 4 times the orbital period of Pair Y. How does the total mass of the stars in Pair X compare to the total mass of the stars in Pair Y?

A)Pair Y has a total mass 2 times greater than Pair X.
B)Pair Y has a total mass 16 times greater than Pair X.
C)Pair X has a total mass 16 times greater than Pair Y.
D)Pair X has a total mass 2 times greater than Pair Y.

Question 63

How did astronomers discover the relationship between spectral type and mass for main sequence stars?

A)by using computer models of hydrogen fusion and stellar structure
B)by measuring stellar radii with very powerful telescopes
C)by measuring the masses and spectral types of main- sequence stars in binary systems
D)by comparing stars with the same spectral type but different luminosities

Question 64

What is the spectral type of a star with strong molecular absorption lines?

A)K
B)M
C)G
D)F

Question 65

All stars are born with the same basic composition, yet stars can look quite different from one another. Which two factors primarily determine the characteristics of a star?

A)its mass and its surface temperature
B)its mass and its stage of life
C)its apparent brightness and its distance
D)its apparent brightness and its luminosity
E)its age and its location in the galaxy

Question 66

How is the lifetime of a star related to its mass?

A)More massive stars live much shorter lives than less massive stars.
B)More massive stars live slightly longer lives than less massive stars.
C)More massive stars live slightly shorter lives than less massive stars.
D)More massive stars live much longer lives than less massive stars.

Question 67

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

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

Question 68

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

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

Question 69

Star A has an apparent magnitude of 3, and Star B has an apparent magnitude of 5. Which star is brighter in our sky?

A)Star A
B)Star B
C)The two stars have the same brightness in our sky, but Star A is closer to us than Star B.
D)There is not enough information to answer the question.

Question 70

Which of the following terms is given to a pair of stars that we can determine are orbiting each other only by measuring their periodic Doppler shifts?

A)spectroscopic binary
B)double star
C)visual binary
D)eclipsing binary

Question 71

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)100 billion years
C)4)6 billion years
D)10 billion years
E)You also need to know the luminosity class of the turn- off point to determine the age.

Question 72

The sketch above shows groups of stars on the H- R diagram, labeled (a)through (e); note that (a)represents the entire main sequence while (c)and (d)represent only small parts of the main sequence. Which group represents stars that are extremely bright and emit most of their radiation as ultraviolet light?

A)a
B)b
C)c
D)d
E)e

Question 73

Which of the following stars has a spectrum that peaks at the shortest wavelength?

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

Question 74

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 75

If the Sun- Earth separation were 10 AU instead of 1 AU, what would the flux of sunlight (energy per second per square meter)be at the Earth, compared to what it is today?

A)100 times more
B)10 times less
C)100 times less
D)10 times more
E)about 3.16 (or the square root of 10)times less

Question 76

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

A)5 light- years.
B)2 parsecs.
C)5 parsecs.
D)0)5 light- year.
E)0)5 parsec.

Question 77

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

Question 78

What is the spectral type of a star with very strong hydrogen absorption lines?

A)G
B)B
C)A
D)F

Question 79

The sketch above shows groups of stars on the H- R diagram, labeled (a)through (e); note that (a)represents the entire main sequence while (c)and (d)represent only small parts of the main sequence. Which group represents stars fusing hydrogen in their cores?

A)a
B)b
C)c
D)d
E)e

Question 80

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