Deck 13: Taking the Measure of Stars

Question 1

Two main-sequence stars have the same temperature.If star A is four times more luminous than star B, then

A) star B is two times farther away than star A.
B) star B is four times farther away than star A.
C) star B is eight times farther away than star A.
D) star B and star A lie at the same distance from us.
E) it is impossible to determine their relative distances from the information given.

Answer 1

star B is two times farther away than star A.

Question 2

A parsec is a measure of

A) time.
B) velocity.
C) distance.
D) luminosity.
E) brightness.

Answer 2

distance.

Question 3

Parallax is used to measure a star's

A) distance.
B) velocity.
C) luminosity.
D) mass.
E) radius.

Answer 3

distance.

Question 4

What is the difference between apparent brightness and luminosity?

A) These are different names for the same property.
B) Luminosity is how much light we see from a star; apparent brightness is how much light it emits.
C) Apparent brightness is how much light we see from a star; luminosity is how much light it emits.
D) Luminosity measures size; brightness measures temperature.
E) Apparent brightness measures size; luminosity measures temperature.

Question 5

Star A and star B appear equally bright, but star A is twice as far away from us as star B. Which of the following is true?

A) Star A is twice as luminous as star B.
B) Star A is four times as luminous as star B.
C) Star B is twice as luminous as star A.
D) Star B is four times as luminous as star B.
E) Star A and star B have the same luminosity because they have the same brightness.

Question 6

If a star's measured parallax is 0.2 arcsec, what is its distance?

A) 2 pc
B) 5 pc
C) 20 pc
D) 40 pc
E) 50 pc

Question 7

You observe two stars in a visual binary system using a blue filter that is centered at a wavelength of 550 nm and a red filter that is centered at a wavelength of 650 nm.Star A has a temperature of 10,000 K, while star B has a temperature of 4000 K, and you know that both stars are the same size.Which star will be brighter in each filter?

A) Star A is brighter in the blue filter, and star B is brighter in the red filter.
B) Star B is brighter in the blue filter, and star A is brighter in the red filter.
C) Star A is brighter in both filters.
D) Star B is brighter in both filters.
E) Both stars have the same brightness in each filter.

Question 8

Star A is a red star.Star B is a blue star.You are able to determine that both stars are the same size.Which star appears brighter in your sky?

A) Star A is brighter.
B) Star B is brighter.
C) They have the same brightness.
D) We also need to know the distance of the stars to determine their brightness.
E) Color is not related to brightness at all.

Question 9

How many arcseconds are there in 1 degree?

A) 60
B) 360
C) 3,600
D) 6,000
E) 36,000

Question 10

What advantage do you gain by having two eyes that are separated on your face, rather than being very close together?

A) better collecting area, which allows you to see dimmer objects
B) double vision, which allows you to see multiple objects at once
C) color vision, which allows you to determine temperatures
D) stereoscopic vision, which allows you to determine distances
E) better magnification, which allows you to see smaller objects

Question 11

Star A and star B both have the same temperature but different sizes and distances.Star A is more luminous than star B, but star B appears brighter than star A in our sky.Which of these statements about the absolute and apparent magnitudes of the two stars is correct?

A) Star A has a larger apparent magnitude and a larger absolute magnitude.
B) Star A has a larger apparent magnitude, while star B has a larger absolute magnitude.
C) Star B has a larger apparent magnitude and a larger absolute magnitude.
D) Star B has a larger apparent magnitude, while star A has a larger absolute magnitude.
E) Both stars have the same apparent and absolute magnitudes.

Question 12

What relationship exists between a star's distance and its parallax?

A) Distance is directly proportional to parallax.
B) Distance is inversely proportional to parallax.
C) Distance is directly proportional to parallax squared.
D) Distance is inversely proportional to parallax squared.
E) Distance and parallax are not related to each other at all.

Question 13

To measure the most accurate parallax possible from Earth's surface, we would make two measurements of a star's position on the sky separated by

A) 6 hours.
B) 12 hours.
C) 24 hours.
D) 6 months.
E) 12 months.

Question 14

The star named Capella has an apparent magnitude of 0, while the star named Polaris has an apparent magnitude of 2.This means that Capella appears ________ in our sky than Polaris.

A) 18 times fainter
B) 6 times fainter
C) 2 times fainter
D) 2 times brighter
E) 6 times brighter

Question 15

Star A is a red star.Star B is a blue star.Which star is hotter?

A) Star A is hotter.
B) Star B is hotter.
C) They are the same temperature.
D) We also need to know the luminosities of the stars to determine their temperatures.
E) Color is not related to temperature at all.

Question 16

If a star's distance is 10 pc, what is its parallax?

A) 0.01 arcsec
B) 0.05 arcsec
C) 0.1 arcsec
D) 0.5 arcsec
E) 1 arcsec

Question 17

The absolute magnitude of a star is a measure of its

A) luminosity.
B) composition.
C) distance.
D) color.
E) radius.

Question 18

If one star appears brighter than another in the night sky, then the brighter star

A) must be the closer star.
B) must be the bigger star.
C) must be the hotter star.
D) must be the redder star.
E) cannot be compared to a dimmer star without more information.

Question 19

The Hipparcos satellite was capable of measuring parallaxes to ________ stars.

A) all of the Milky Way galaxy's 400 billion
B) 200 million
C) 120,000
D) 1,500
E) 116

Question 20

Star A is a red star.Star B is a blue star.You are able to determine that both stars are the same size.Which star is more luminous?

A) Star A is more luminous.
B) Star B is more luminous.
C) They have the same luminosities.
D) We also need to know the distance of the stars to determine their luminosity.
E) We cannot tell because color is not related to luminosity.

Question 21

Why do O- and B-type stars have weaker hydrogen absorption lines than A-type stars?

A) O- and B-type stars are cooler than A-type stars.
B) O- and B-type stars are smaller than A-type stars.
C) A larger fraction of hydrogen atoms in O- and B-type stars is ionized.
D) O- and B-type stars have converted much more of their hydrogen into heavier elements.
E) A-type stars have a higher mass than O- and B-type stars, so they have more hydrogen.

Question 22

Which stars show the largest amount of absorption from molecules such as TiO and CN?

A) the least massive main-sequence stars
B) the most massive main-sequence stars
C) only main-sequence stars with masses close to 1 solar mass
D) only red giant stars
E) only A-type stars

Question 23

Star C is a red star.Star D is a blue star.Which has a larger radius?

A) Star C has a larger radius.
B) Star D has a larger radius.
C) Stars C and D have the same radius.
D) We also need to know the luminosities of the stars to determine their radii.
E) We also need to know the age of the stars to determine their radii.

Question 24

Star E is the same temperature as star F, but star E is four times as luminous as star F.How do the radii of the stars compare?

A) The radius of star E is twice that of star F.
B) The radius of star E is four times that of star F.
C) The radius of star F is twice that of star E.
D) The radius of star F is four times that of star E.
E) The radii are the same length.

Question 25

A type G star is always ________ when compared to a type A star.

A) larger in radius
B) bluer in color
C) lower in temperature
D) more luminous
E) composed of more hydrogen

Question 26

What spectral class is the Sun?

A) A0
B) B7
C) F5
D) M3
E) G2

Question 27

Two stars with similar temperatures but different sizes will have

A) similar spectral types but different luminosities.
B) similar luminosities but different brightnesses.
C) similar brightnesses but different distances.
D) similar distances but different masses.
E) similar masses but different spectral types.

Question 28

If star A has a temperature that is twice as hot as the Sun, but it has the same luminosity as the Sun, the diameter of star A must be ________ times the diameter of the Sun.

A) 16
B) 4
C) 2
D) 1/2
E) 1/4

Question 29

Which spectral type has the strongest hydrogen absorption lines?

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

Question 30

Stars are made mostly of

A) helium.
B) oxygen.
C) hydrogen.
D) nitrogen.
E) carbon.

Question 31

The bright star named Rigel has a luminosity of 66,000 L_SUN and a temperature of 11,000 K.What is its radius? Note that the temperature of the Sun is 5800 K.

A) 5 R_SUN
B) 30 R_SUN
C) 70 R_SUN
D) 135 R_SUN
E) 190 R_SUN

Question 32

If we know the temperature and luminosity of a star, we can also calculate its

A) radius.
B) mass.
C) chemical composition.
D) brightness.
E) all of the above

Question 33

The fraction of the Sun's mass that is made of heavy elements is

A) 0.5 percent.
B) 2 percent.
C) 10 percent.
D) 20 percent.
E) 50 percent.

Question 34

What property of light allows astronomers to measure the motions of spectroscopic binary stars?

A) quantization of energy
B) the varying speed of light
C) polarization
D) the Doppler effect
E) refraction

Question 35

Which sequence correctly lists the spectral classes of stars in order from hottest to coolest?

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

Question 36

The spectral class of a star is related to its

A) luminosity.
B) brightness.
C) radius.
D) mass.
E) temperature.

Question 37

Which of the following is directly measurable from the absorption lines of a star?

A) the luminosity of the star
B) the chemical composition of the star
C) the mass of the star
D) the distance to the star
E) the age of the star

Question 38

Stars that have spectral type B ________ in temperature compared with stars that have spectral type M.

A) are cooler
B) are hotter
C) are the same
D) usually hotter but sometimes cooler
E) usually cooler but sometimes hotter

Question 39

When astronomers refer to "heavy elements," which elements are they talking about?

A) all elements
B) all elements more massive than hydrogen
C) all elements more massive than helium
D) all elements more massive than carbon
E) all elements more massive than iron

Question 40

What type of spectrum do most stars produce?

A) an absorption spectrum on top of a blackbody spectrum
B) an emission spectrum on top of a blackbody spectrum
C) an absorption spectrum on top of an emission spectrum
D) a pure emission spectrum
E) a pure blackbody spectrum

Question 41

The figure below shows an H-R diagram, with five stars labeled A through E.Which star has the highest luminosity?

A) A
B) B
C) C
D) D
E) E

Question 42

Which properties can be plotted on the horizontal axis of an H-R diagram?

A) luminosity, apparent magnitude, and absolute magnitude
B) luminosity, color, and spectral class
C) temperature, color, and spectral class
D) temperature and luminosity
E) spectral class only

Question 43

For which type of binary system are astronomers able to resolve each of the two stars individually?

A) eclipsing binary
B) spectroscopic binary
C) visual binary
D) binaries in which the two stars have the same mass
E) binaries in which the two stars have the same luminosity

Question 44

On a typical H-R diagram, where are the stars with the largest radii located?

A) in the upper left corner
B) in the upper right corner
C) in the center
D) in the lower left corner
E) in the lower right corner

Question 45

A star's position in the H-R diagram is determined by its

A) temperature and size.
B) temperature and distance.
C) brightness and size.
D) mass and distance.
E) brightness and distance.

Question 46

Binary star systems are extremely useful in studying stars because they allow us to determine star

A) temperatures.
B) sizes.
C) masses.
D) distances.
E) spectral types.

Question 47

Astronomers can measure the speed of the stars in a binary system by measuring the ________ of the stars.

A) temperatures
B) luminosities
C) distances
D) sizes
E) spectra

Question 48

Roughly what percentage of stars in our galaxy are main-sequence stars?

A) 10 percent
B) 25 percent
C) 50 percent
D) 75 percent
E) 90 percent

Question 49

The figure below shows an H-R diagram, with five stars labeled A through E.Which star has the highest temperature?

A) A
B) B
C) C
D) D
E) E

Question 50

You discover a binary star system in which star A has a velocity of 10 km/s and star B has a velocity of 30 km/s.If you study the system further and find out that the orbital period is 30 days and the orbital separation is a constant 0.3 AU, then what are the masses of stars A and B?

A) Star A is 3M_SUN, and star B is 1M_SUN.
B) Star A is 1M_SUN, and star B is 0.3M_SUN.
C) Star A is 6M_SUN, and star B is 2M_SUN.
D) Star A is 2M_SUN, and star B is 0.5M_SUN.
E) Star A is 0.3M_SUN, and star B is 1M_SUN.

Question 51

Star X and star Y are 5 AU apart from each other.Star X is four times as massive as star Y.The center of mass of this system is ________ AU away from star X and ________ AU away from star Y.

A) 3; 2
B) 2; 3
C) 2.5; 2.5
D) 1; 4
E) 4; 1

Question 52

Main-sequence stars range in mass from approximately

A) 0.5 to 10 M_SUN.
B) 0.08 to 150 M_SUN.
C) 1 to 100 M_SUN.
D) 0.5 to 75 M_SUN.
E) 5 to 50 M_SUN.

Question 53

Eclipsing binary systems

A) orbit in the plane of the sky.
B) exhibit large radial velocity shifts.
C) contain stars of equal mass.
D) contain stars that pass in front of one another during their orbit.
E) contain stars that can be resolved as two separate stars.

Question 54

The figure below shows an H-R diagram, with five stars labeled A through E.Which of the main-sequence stars has the smallest mass?

A) A
B) B
C) C
D) D
E) E

Question 55

The faster-moving star in a binary is the

A) less massive star.
B) more massive star.
C) smaller-radius star.
D) larger-radius star.
E) lower-temperature star.

Question 56

The Hertzsprung-Russell diagram is a graph of ________ for stars.

A) mass versus brightness
B) size versus mass
C) luminosity versus temperature
D) mass versus spectral type
E) luminosity versus brightness

Question 57

What type of star is most common in the solar neighborhood?

A) subgiant
B) supergiant
C) white dwarf
D) giant
E) main-sequence

Question 58

The figure below shows an H-R diagram, with five stars labeled A through E.Which star has the smallest radius?

A) A
B) B
C) C
D) D
E) E

Question 59

In a binary star system that contains stars with 2M_SUN and 1M_SUN, the velocity of the 2M_SUN star will be ________ times the velocity of the 1M_SUN star.

A) 0.2
B) 0.5
C) 1
D) 2
E) 3

Question 60

Which stars are the most common?

A) stars with a mass and a radius larger than the Sun's
B) stars with a smaller mass and radius than the Sun's
C) stars with a mass larger than the Sun's and a radius smaller than the Sun's
D) stars with a mass smaller than the Sun's and a radius larger than the Sun's
E) All of these are equally common.

Question 61

The stars that have the largest radii are classified as

A) main-sequence stars.
B) blue supergiants.
C) red supergiants.
D) white dwarfs.
E) subgiants

Question 62

Explain how astronomers can use the blue and visible filters to determine the temperatures of stars.

Question 63

A star with a stellar parallax of 0.025 arcsecond has a distance of how many parsecs?

Question 64

The stars that have the largest radii are classified as

A) giants.
B) ultragiants.
C) supergiants.
D) megagiants.
E) supernovae.

Question 65

The blackbody spectra of a star with a temperature of 6000 K and a star with a temperature of 4000 K are shown in the figure below.An astronomer uses a telescope to observe each of these two stars in both the blue and red filters.The blue filter is centered at 450 nm, while the red filter is centered at 660 nm.For each of the two stars, indicate through which filter that star will be brighter.Explain your answer.

Question 66

If a star's parallax is measured using identical telescopes, one on Earth and the other on Mars, which planet's telescope would measure the bigger parallax? Explain your answer.

Question 67

The one property of a main-sequence star that determines all its other properties is its

A) luminosity.
B) mass.
C) temperature.
D) spectral type.
E) brightness.

Question 68

Spectroscopic parallax refers to

A) using a star's position on the H-R diagram to infer its distance.
B) using a star's spectrum to measure its radial velocity.
C) using a star's Doppler shift to infer its distance.
D) using Earth's motion to measure a star's apparent "wobble" to infer its distance.
E) measuring a star's physical "wobble" in the sky to determine its mass.

Question 69

How is the unit of length known as a parsec defined?

Question 70

The sequence of stellar spectral types is shown in the figure below.Explain why the hottest star (O5) has so little emission in the visible portion of the spectrum (450-700 nm), spectral types F-K show the most emission in the visible band, and still cooler stars (M type) once again show very little in the visible band.

Question 71

What is the approximate luminosity of a 5 M_SUN main-sequence star?

A) 0.2 L_SUN
B) 5.0 L_SUN
C) 30 L_SUN
D) 450 L_SUN
E) 10,000 L_SUN

Question 72

A star's location on the main sequence is determined entirely by its

A) mass.
B) composition.
C) distance.
D) size.
E) radial velocity.

Question 73

The brightest stars in the sky also tend to be

A) the oldest stars.
B) the reddest stars in the sky.
C) very near to us (within 5 parsecs).
D) very luminous.
E) the smallest stars.

Question 74

The habitable zone of a star is the region around that star where

A) life has been confirmed to exist.
B) Earth-sized planets are most likely to exist.
C) solar power will be the most efficient.
D) the temperature of a planet in this region may support liquid water.
E) oxygen atmospheres will be stable.

Question 75

If you want to use an Earth-based telescope to measure the distance to a star via measuring its parallax, how far apart should your observations of the star ideally be, and why?

Question 76

A star classified as a K0III star is

A) a giant that is cooler than the Sun.
B) a supergiant that is hotter than the Sun.
C) a main-sequence star that is hotter than the Sun.
D) a subgiant that is cooler than the Sun.
E) a dwarf that is hotter than the Sun.

Question 77

A star in the lower-left corner of the H-R diagram must be

A) large and hot.
B) large and cold.
C) small and cold.
D) small and hot.
E) none of these

Question 78

Rigel is a star with an apparent magnitude of +0.1, and Betelgeuse is a star with an apparent magnitude of +0.4.Which star appears brighter, and what is the ratio of their brightness?

Question 79

Star A is exactly the same color as star B and appears equally bright.Through stellar parallax measurements, we find that star B is twice as far away from us as star A.Determine which star has the larger radius and how much larger it is.

Question 80

If the Hubble Space Telescope can see stars as faint as magnitude 30, how much fainter are these stars than the faintest ones you can see in a very dark night sky, which have magnitude 6?