Deck 10: Observing Properties of Distant Stars

Question 1

The most common type of star is a blue supergiant.

Answer 1

False

Question 2

White dwarfs are approximately the same size as Earth.

Answer 2

True

Question 3

A few rare stars are considerably bigger and brighter than typical giants,with up to 1000 solar radii,and are called supergiants.

Answer 3

True

Question 4

Blue stars are relatively hot,with high surface temperatures.

Question 5

The key to finding a star's radius from its luminosity and surface temperature is the Stefan-Boltzmann law.

Question 6

Red stars are relatively cool compared with other stars,with low surface temperatures.

Question 7

The H-R diagram plots the pressure of a star versus its gravity.

Question 8

How bright a star appears in the sky for an Earth-based observer is called its apparent magnitude.

Question 9

A star with a parallax angle of 1 second of arc is defined to have a distance of 1 light-year.

Question 10

Spectroscopic parallax is the process of finding the distance to a star by measuring its shift against the background stars over 6 months.

Question 11

If two stars of different luminosity have the same temperature,a luminosity class II star will be smaller than a luminosity class V star.

Question 12

A magnitude +4 star is twice as bright as a magnitude +2 star.

Question 13

If two stars of different luminosity have the same temperature,a luminosity class III star will be smaller than a luminosity class I star.

Question 14

Red stars are hot and blue stars are cold.

Question 15

A star that is spectral class A is hotter than a star of spectral class O.

Question 16

The smaller angle through which a star's apparent position changes due to the change in position of an observer,the greater the distance it is from the observer.

Question 17

Without a telescope,the brightest stars are magnitude 6 stars and the dimmest stars are magnitude 1 stars.

Question 18

By analyzing a star's spectra,the chemical composition,the spectral type,and the luminosity class can be determined.

Question 19

If you bring an object to half of the original distance,the apparent brightness will be 4 times as bright as before.

Question 20

If you triple the distance to a given star,the apparent brightness will be one-third as bright as before.

Question 21

Sirius,in Canis Major (the large hunting dog of Orion),is the brightest star in the winter night sky.It has a parallax angle of 0.38 seconds of arc.Orion's other hunting dog,Canis Minor,has as its brightest star Procyon,with a parallax angle of 0.29 seconds of arc.Vega,in Lyra the Lyre (Harp),is the brightest star in the summer night sky.It has a parallax angle of 0.13 seconds of arc.Which of these stars is farthest away?

A) Sirius
B) Procyon
C) Vega
D) It cannot be determined from this information alone.

Question 22

In order to measure the parallax angle of a star,it is necessary to know the direction to the star on two different days of the year and

A) nothing else.
B) the star's luminosity (total energy output per second).
C) the star's surface temperature.
D) the star's spectrum.

Question 23

Two stars in our sky have the same apparent brightness.If neither of them is hidden behind gas or dust clouds,then we know that they

A) may be at different distances,in which case the nearest one must have the greater luminosity.
B) may be at different distances,in which case the farther one must have the greater luminosity.
C) must have the same temperature.
D) must be at the same distance away from us.

Question 24

Stellar parallax exists because

A) Earth moves in space.
B) stars move in space.
C) Earth rotates about its own axis.
D) stars have size (they are not really just points of light).

Question 25

Light,leaving a point source,spreads out so that the apparent brightness,b,of light per unit area varies with distance d according to which law ( $\alpha$ means "proportional to")?

A) b $\alpha$ 1/d².
B) b = constant.
C) b $\alpha$ 1/d.
D) b $\alpha$ d².

Question 26

Suppose that two identical stars (having the same total light output or luminosity)are located such that star A is at a distance of 5 pc and star B is at a distance of 25 pc.How will star B appear,compared to star A?

A) 1/22 as bright
B) 1/25 as bright
C) 1/20 as bright
D) 1/5 as bright

Question 27

As you drive along a road,trees in the middle distance seem to shift in position relative to faraway hills.What name is given to this phenomenon?

A) Doppler effect
B) Inverse-square law
C) Perspective
D) Parallax

Question 28

If Star A has an apparent magnitude of +5,and Star B has an apparent magnitude of +10,then

A) Star A is twice as bright as Star B.
B) Star B is twice as bright as Star A.
C) Star A is 100 times as bright as Star B.
D) Star B is 100 times as bright as Star A.

Question 29

If stellar parallax can be measured to a precision of about 0.01 arcsec using telescopes on Earth to observe stars,to what distance does this correspond in space?

A) 500 pc
B) 200 pc
C) 100 pc
D) 0.01 pc

Question 30

What is the relationship between stellar parallax (p)measured in seconds of arc and distance (d)measured in parsecs?

A) d = 2p
B) d = p
C) 1/d = 2p
D) p = 1/d

Question 31

Star A has a luminosity L_A = 100 L and it is 1000 pc away.Star B has the same luminosity as the Sun,L,and it is 100 pc away.What can you say about the brightness of these two stars?

A) Star A is brighter than Star B.
B) Star B is brighter than Star A.
C) Star A and Star B have the same brightness.
D) It is not possible to determine the answer without knowing L,the luminosity of the Sun.

Question 32

The relative brightness of stars as we see them in our sky are represented on star charts in terms of their

A) surface temperatures.
B) absolute magnitudes.
C) apparent magnitudes.
D) luminosities.

Question 33

Which of the following is one of the facts that must be known in order to determine the distance to a star by parallax?

A) The star's spectral type
B) The star's apparent magnitude
C) The wavelength at which the star's spectrum is most intense
D) The distance between the Sun and Earth

Question 34

Luminosity is measured in

A) watts per square meter.
B) joules per second or watts.
C) parsecs.
D) arcseconds per year.

Question 35

Parallax of a nearby star is used to estimate its

A) distance from Earth.
B) apparent magnitude.
C) physical size or diameter.
D) surface temperature.

Question 36

The luminosity of a star is

A) another name for its color or surface temperature.
B) its brightness as seen by people on Earth.
C) its total energy output into all space over all wavelengths.
D) its brightness at a hypothetical distance of 10 parsecs (32.6 light-years)from Earth.

Question 37

If the Hipparcos satellite measures the parallax motion of a star against the background stars and concludes that the star has a parallax of 0.004 arcsec,how far is that star from Earth?

A) 250 pc or 800 ly
B) 0.004 pc or 0.013 ly
C) 25 pc or 81 ly
D) 400 pc or 1300 ly

Question 38

Parallax is the

A) distance to an object,measured in parsecs.
B) angle subtended by an object,as seen by us.
C) apparent shift in position of a nearby object as we move.
D) shift in position of an object as it moves.

Question 39

What does apparent magnitude tell us about a star?

A) Its size compared to the Sun
B) The intrinsic brightness of a star (the total light actually emitted by the star )
C) The brightness of a star as it appears in our sky
D) The brightness the star would appear to have if it were exactly 10 pc from Earth

Question 40

We can tell that some stars are relatively close to us in the sky because

A) they appear to move periodically back and forth against the background stars because of Earth's movement around the Sun.
B) they appear to be extremely bright.
C) they are occasionally occulted or eclipsed by our Moon.
D) the light from these stars shows only a very small redshift caused by the universal expansion of the universe.

Question 41

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

A) either larger or smaller than the absolute magnitude,depending on the temperature and diameter of the star.
B) a smaller number than the absolute magnitude.
C) a larger number than the absolute magnitude.
D) the same as the absolute magnitude because magnitude is independent of distance.

Question 42

What is the approximate ratio of the brightness of two stars whose apparent magnitudes differ by 1 magnitude?

A) 2.5
B) 10
C) 100
D) 2

Question 43

Which of the following atoms or ions will produce strong absorption lines in the spectra of stars with relatively cool surface temperatures?

A) TiO,molecules of titanium oxide
B) He I,neutral helium
C) Mg II,ionized magnesium
D) Ca II,ionized calcium

Question 44

In the spectral classification of stars,strong absorption lines of which of the following atomic or molecular constituents would indicate very low surface temperature?

A) He II
B) Fe II
C) Mg II
D) TiO

Question 45

The Sun's absolute magnitude is about +5.The brightest stars in our sky have absolute magnitudes of about -10.What is the luminosity of these stars compared to the Sun,assuming that they have similar spectral light distributions?

A) 1 million times larger
B) 5 times less
C) 1 million times smaller
D) 15 times greater

Question 46

Spectral classification determines a nearby star's surface temperature by examining the

A) peak wavelength of the star spectrum.
B) relative intensities of light measured through different wavelength band filters.
C) pattern of spectral "absorption" lines from various atoms.
D) the overall shape of the star's spectrum compared to a black body.

Question 47

The spectral class of the Sun is G2 and the star Enif is K2.From this information,we know that Enif is

A) farther away from the Sun.
B) cooler than the Sun.
C) intrinsically brighter than the Sun.
D) hotter than the Sun.

Question 48

The star Alderamin has an apparent magnitude of 2.4 and an absolute magnitude of 1.4.From this information (assuming that the starlight has not been dimmed by interstellar clouds),we can say for certain that Alderamin is

A) less than 10 AU away.
B) more than 10 parsecs away.
C) less than 10 light-years away.
D) less than 10 parsecs away.

Question 49

The star Alphard has an apparent magnitude of 2.0,and the star Megrez has an apparent magnitude of 3.3.The only thing that can be said with certainty about Alphard is that it

A) is brighter than Megrez,as seen in our sky.
B) has a greater luminosity than Megrez.
C) is closer than Megrez.
D) is fainter than Megrez,as seen in our sky.

Question 50

The spectral type of a star is most directly related to (and determines uniquely)its

A) size or radius.
B) absolute magnitude.
C) luminosity.
D) surface temperature.

Question 51

Stars of spectral type O,the hottest blue-white stars,have spectra characterized by

A) the strongest hydrogen lines of any spectral type.
B) spectra of complex molecules.
C) very few spectral lines.
D) very intense spectral lines all across the spectrum.

Question 52

The Sun's spectrum peaks in the green region of the spectrum (i.e. ,green is the most intense color in its spectrum).The spectrum of Rigel (the knee of Orion)peaks in the short wavelength end of the visible spectrum.Compared with the Sun,Rigel is

A) cooler and redder.
B) hotter and redder.
C) cooler and whiter.
D) hotter and whiter.

Question 53

Which of the following four spectral classifications represents the hottest stellar surface temperature?

A) K
B) A
C) G
D) B

Question 54

The spectral sequence of star surface temperature,as determined by relative spectral absorption line strengths,has been given which sequence of letters,in order of decreasing temperature?

A) MOFKGAB
B) OFMGABK
C) OBAFGKM
D) ABFGKMO

Question 55

What is "metal" to an astronomer?

A) Any element heavier than hydrogen
B) Any element heavier than hydrogen or helium
C) Any element in solid or liquid form that can conduct electricity easily
D) Any element

Question 56

A star of spectral class L is

A) a red star,intermediate between spectral classes K and M.
B) not a star at all,but a white dwarf.
C) a yellow star like the Sun.
D) not a star at all,but a brown dwarf.

Question 57

The chemical makeup of a star's surface is usually determined by

A) spectroscopy of the light emitted by the star.
B) examining the chemicals present in a meteorite.
C) theoretical methods,considering evolution of the star.
D) taking a sample of the star's surface with a probe.

Question 58

The Henry Draper Catalog of stellar classifications was developed beginning in the late nineteenth century.It originally classified stars according to the strengths of their hydrogen lines.By the 1920s,however,the sequence had been reorganized so that the stars were classified by surface temperature.What important scientific development made possible this reinterpretation?

A) The discovery of nuclear physics and how stars generate their energy
B) The discovery of blackbody radiation and the blackbody curve
C) The development of atomic physics and how atoms emit light
D) The development of radio astronomy and the detection of molecules in space

Question 59

At what distance are stars assumed to be from Earth when they are represented by their absolute (as opposed to their apparent)magnitude?

A) 10 ly
B) 10 parsecs
C) 10 AU
D) 1 ly

Question 60

In order of decreasing temperature,the complete spectral sequence for stars and brown dwarfs,as determined by relative spectral absorption line strengths,is

A) OFMGABKLT.
B) ABFGKLMOT.
C) OBAFGKMLT.
D) LMOFKGABT.

Question 61

Measurements indicate that a certain star has a very high intrinsic brightness (100,000 times as bright as our Sun),yet is relatively cool (3500 K).How can this be?

A) There must be an error in observation because no star can have this form.
B) The star must be quite small.
C) The star must belong to the main sequence.
D) The star must be very large.

Question 62

The spectral luminosity class of the star Spica is B1 V,and that of the star $\tau$ Ceti is G8 V.From this (with luminosity measured in solar luminosities),we know for sure that

A) " $\tau$ Ceti is hotter but has the same luminosity as Spica."
B) " $\tau$ Ceti is cooler but has the same luminosity as Spica."
C) " $\tau$ Ceti is cooler and has a lower luminosity than Spica."
D) " $\tau$ Ceti is hotter and has a lower luminosity than Spica."

Question 63

What is the difference between an optical double star and a visual binary star?

A) There is no difference: They are two names for the same thing.
B) Optical double stars can be seen as separate stars only through a telescope,whereas visual binaries can be seen with the unaided eye (e.g. ,the star Mizar in the Big Dipper's handle).
C) The stars in an optical double star are actually orbiting each other,whereas a visual binary is an illusion: The stars are at vast distances from each other and are not actually orbiting each other.
D) An optical double is an illusion: The stars are at vast distances from each other and are not actually orbiting each other,whereas in a visual binary,the stars are actually orbiting each other.

Question 64

Compared with a star in the middle left of the diagram,a star in the lower left part of the Hertzsprung-Russell diagram is

A) brighter.
B) smaller.
C) cooler.
D) larger.

Question 65

Spectroscopic parallax is the

A) apparent change in position of the absorption lines in a star's spectrum due to the Doppler shift,caused by Earth's motion around the Sun.
B) apparent change in position of a nearby star compared to distant background stars,due to the motion of Earth around the Sun.
C) change in position of the absorption lines in a star's spectrum due to the Doppler shift,caused by the star's motion around the center of mass in a binary star system.
D) distance to a star measured using the spectral luminosity class of the star and the inverse-square law.

Question 66

The Hertzsprung-Russell diagram is a plot of

A) apparent brightness versus intrinsic brightness or luminosity of a group of stars.
B) luminosity versus period of variation for variable stars.
C) apparent brightness versus distance for stars near the Sun.
D) intrinsic brightness or luminosity versus temperature of a group of stars.

Question 67

The point around which two stars of unequal mass in a binary system appear to revolve is

A) closest to the more massive star.
B) halfway between the two star centers.
C) at the center of the more massive star.
D) closest to the less massive star.

Question 68

As you move upward and to the left on the H-R diagram,the stars become

A) cooler and redder.
B) hotter and redder.
C) cooler and whiter.
D) hotter and whiter.

Question 69

How do two unequal mass stars move around each other in a binary system?

A) In a common elliptical orbit,always remaining diametrically opposite to each other through one of the foci of the ellipse
B) In straight lines,back and forth past each other
C) In elliptical orbits,about a common "center of mass"
D) The low-mass star moves in a circular orbit around the stationary high-mass star.

Question 70

An important aspect of binary star systems,as distinct from single stars,is that they allow a

A) verification of the Doppler shift.
B) measurement of the overall shapes of stars.
C) measurement of the universal gravitational constant.
D) measurement of the masses of stars.

Question 71

The star Arcturus is classified as K2 III,which means that it is a

A) hot giant.
B) cool giant.
C) cool main-sequence star.
D) cool supergiant.

Question 72

Two stars are found to have the same luminosity.However,one star has twice the surface temperature of the other.From this information,what can you determine about their radii?

A) The hotter star has half the radius of the cooler star.
B) The cooler star has half the radius of the hotter star.
C) The hotter star has a quarter the radius of the cooler star.
D) Nothing can be determined about the radii from this information.

Question 73

Barnard's star,one of our nearest neighbors,is classified as M5 V.This means that it is a

A) cool giant.
B) hot main-sequence star.
C) cool supergiant.
D) a cool main-sequence star.

Question 74

Which of the following four spectral luminosity classes would correspond to a red supergiant?

A) B7 I
B) G2 III
C) M3 V
D) M2 I

Question 75

A white dwarf is

A) an object intermediate between planets and stars that will never become a star.
B) a star at the end of its life,with a size close to that of Earth.
C) any main-sequence star with a surface temperature between about 9000 K and 15,000 K.
D) a star at the beginning of its life,with a size 2-10 times that of the Sun.

Question 76

What is the size of a star in the upper right part of the Hertzsprung-Russell diagram compared to one in the middle of the diagram?

A) It is fainter.
B) It is hotter.
C) There are no stars in the upper right part of the diagram.
D) It is larger.

Question 77

Which important stellar parameter can be determined by the study of binary stars?

A) The age of the stars
B) Stellar masses
C) Surface temperatures of the stars
D) The distance of the stars from Earth

Question 78

If you compare two stars,the one with the

A) larger radius must have the greater luminosity.
B) higher surface temperature must have the greater luminosity.
C) smaller absolute magnitude must have the greater luminosity.
D) larger surface area has the greater energy flux from its surface.

Question 79

Two stars,one classified A4 V and the other F8 V,have the same apparent magnitude.There is no significant amount of absorption of starlight by interstellar material.From this information we know that

A) the A4 V star is closer to the Sun than F8 V.
B) the A4 V star is smaller than F8 V.
C) the A4 V star is farther from the Sun than F8 V.
D) both stars are at the same distance from Sun.

Question 80

Where on the Hertzsprung-Russell diagram do most local stars in our universe congregate?

A) In the supergiant area,where the most massive stars spend a significant time
B) In the giants area,where most stars spend the longest time of their lives
C) In the white dwarf area,the "graveyard" of stars
D) On the main sequence where stars are generating energy by fusion reactions