Deck 18: The Stars: a Celestial Census

Question 1

I am measuring the spectrum of the stars in a spectroscopic binary system. When one of the stars is moving toward the Earth in its orbit, we observe

A) that the lines in its spectrum get brighter
B) that the lines in its spectrum merge with the lines of the other star
C) that it is no longer possible to learn what elements are in the star
D) that the lines in its spectrum show a blue-shift
E) none of the above

Answer 1

that the lines in its spectrum show a blue-shift

Question 2

An H-R Diagram plots the luminosity of stars against their:

A) mass
B) diameter
C) surface temperature
D) age
E) location in the sky

Answer 2

surface temperature

Question 3

Why can astronomers not measure the diameters of stars directly?

A) stars are so bright, their light burns out all the delicate instruments we would use to measure their diameters
B) all stars change their diameters regularly, growing alternately larger and smaller
C) stars are so far away, we cannot resolve (distinguish) their diameters
D) stars are all in binary systems, and we can only see the combined diameter of both stars
E) you can't fool me; measuring the diameter of any star is a relatively easy process

Answer 3

stars are so far away, we cannot resolve (distinguish) their diameters

Question 4

Which law do astronomers use to determine the masses of the stars in a spectroscopic binary system?

A) Wien's Law
B) Kepler's Third Law
C) Stefan-Boltzmann Law
D) Hubble's Law
E) Jenny Craig's Law

Question 5

Stars on the main sequence obey a mass-luminosity relation. According to this relation,

A) the lower the mass, the higher the luminosity
B) if you double the mass, you get double the luminosity
C) luminosity is proportional to mass to the fourth power (luminosity increases strongly with mass)
D) bright stars have more mass around them in the form of planets, comets, and asteroids
E) the brightest stars are made of such light materials they hardly have any mass at all
Section 18.3: Diameters of Stars

Question 6

Two stars that are physically associated (move together through space) are called

A) double stars
B) main sequence stars
C) brown dwarf pairs
D) first contact stars
E) binary stars

Question 7

The most common kinds of stars in the Galaxy have

A) low luminosity compared to the Sun
B) spectra that show they contain mostly carbon
C) enormous masses compared to the Sun
D) diameters thousands of times greater than the Sun's
E) a dozen or more stars in close orbit around them
Section 18.2: Measuring Stellar Masses

Question 8

Some "superstars" give off more than 50,000 times the energy of the Sun. Why are there no such stars among the stars that are close to the Sun?

A) because conditions in the "neighborhood" of the Sun only permit low-mass (low luminosity) stars to form
B) because such very luminous stars are extremely rare, and thus any small neighborhood in the Galaxy is unlikely to contain one of them
C) because all stars in the vicinity of the Sun have planets, and planets rob a star of its brightness
D) because such superstars only give off a lot of energy for a year or so, before they die
E) because such superstars are really several hundred stars blending their light together (but so far away we can't distinguish individual stars); nearby stars are easy to separate

Question 9

Which of the following statements about spectroscopic binary stars is FALSE?

A) visually we can only see one star
B) some of the lines in the spectrum are double, with the spacing changing over time
C) an analysis of the ways the lines in the spectrum change allows us to calculate the star's distance directly
D) we can use the spectrum to determine the sum of the masses of the two stars
E) we can often use the changes in the positions of the spectral lines to measure the radial velocity of the stars in the system

Question 10

Most of the stars we can see with the unaided eye from Earth are

A) intrinsically fainter than the Sun
B) very close to us (among the closest stars)
C) more luminous (intrinsically brighter) than the Sun
D) only visible to our eyes because they actually consist of three or more stars blending their light together
E) undergoing some sort of explosion which makes their outer layers unusually bright

Question 11

Which of the following characteristics of a single star (one that moves through space alone) is it difficult to measure directly?

A) its apparent brightness
B) its temperature
C) its chemical composition
D) its mass
E) you can't fool me, all of these are quite easy to measure directly

Question 12

For what type of star can astronomers measure the diameter with relative ease?

A) visual double stars
B) white dwarf stars
C) main sequence stars
D) eclipsing binary stars
E) any star that is not a brown dwarf
Section 18.4: The H-R Diagram

Question 13

Which of the following is a method for measuring the diameter of a star?

A) watching the body of the Moon go across the star
B) getting the light curve of an eclipsing binary star
C) comparing the color of a star seen high above our heads and then again when it's near the horizon
D) measuring the spectrum of a spectroscopic binary
E) more than one of the above

Question 14

Stars that do not have what it takes to succeed as a star (i.e. do not have enough mass to fuse hydrogen into helium at their centers) are called:

A) extras
B) red giants
C) spectroscopic stars
D) brown dwarfs
E) main sequence stars

Question 15

Ninety percent of all stars (if plotted on an H-R diagram) would fall into a region astronomers call:

A) the supergiant region
B) the main sequence
C) the white dwarf region
D) the visual region
E) the twilight zone

Question 16

Most of the really bright stars in our sky are NOT among the stars that are very close to us. Why then do they look so bright to us?

A) we see them in crowded regions of stars, which give us the impression that the stars there are brighter than they really are
B) all the brightest stars are red, and red color is much easier to see against the black night sky
C) these stars vary in brightness (flashing brighter and dimmer) and are thus easier to notice
D) these stars are intrinsically so luminous, that they can easily be seen even across great distances
E) actually, this is just an optical illusion; all stars are really the same brightness

Question 17

Which of the following has the smallest mass?

A) a brown dwarf
B) a planet
C) the Sun
D) the smallest mass star that can still have fusion of hydrogen to helium in its core
E) you can't fool me, all the above have roughly the same mass

Question 18

In an H-R diagram, where can you see the spectral type of a star (whether it is an O type star or a G type star, for example)?

A) along the right (vertical axis)
B) along the bottom (the horizontal axis)
C) only in the red giant region
D) only on the main sequence
E) H-R diagrams have nothing to say about spectral types

Question 19

Who was the astronomer who is the "H" in H-R diagram?

A) Hubble
B) Humason
C) Hertzsprung
D) Huggins
E) Hoyle

Question 20

What was the first evidence that gravity outside our solar system worked the same way as it does inside?

A) Galileo saw through his early telescope that the Milky Way consisted of many stars
B) Herschel measured the two stars that make up the Castor system moved around each other
C) Cannon measured different lines in the spectra of different types of stars
D) Comet Halley returned after a 76-year absence
E) You can't fool me, we still don't know whether gravity around other stars works the same way as it does here

Question 21

Stars that lie in different places on the main sequence of the H-R diagram differ from each other mainly by having different:

A) compositions
B) internal structure
C) masses
D) radial velocities
E) ways that they formed

Question 22

A star that is quite hot and has a very small radius compared to most stars is called

A) a main-sequence star
B) an O-type star
C) a red giant
D) a white dwarf
E) an M-type star

Question 23

Imagine that powerful telescopes in the future give us a truly representative sampling of all the stars in the Sun's cosmic neighborhood. Where on the H-R diagram would most of the stars in our immediate vicinity lie?

A) in the upper right, among the supergiants
B) in the upper left, among the bright main sequence stars
C) in the middle of the main sequence, roughly where the Sun is
D) in the lower left, among the white dwarfs
E) in the lower right, among the least luminous main sequence stars

Question 24

A team of astronomers discovers one of the most massive stars ever found. If this star is just settling down in that stage of its life where it will be peacefully converting hydrogen to helium in its core, where will we find it on the H-R diagram?

A) among the supergiants, in the upper right
B) a little bit below the Sun on the main sequence
C) among the most brilliant of the white dwarfs, in the lower left
D) near the very top of the main sequence, in the upper left
E) it could be anywhere on the diagram; we would need more information to determine its place

Question 25

One of your good friends who is on a diet asks you to point out the stars with the smallest mass on an H-R diagram that you are studying. Where are you sure to find the stars with the lowest mass on any H-R diagram?

A) among the white dwarfs
B) among the stars at the top left of the main sequence
C) among the stars at the bottom right of the main sequence
D) among the supergiants
E) stars with low mass can be located anywhere at all in the H-R diagram

Question 26

A white dwarf, compared to a main sequence star with the same mass, would always be:

A) larger in diameter
B) smaller in diameter
C) the same size in diameter
D) younger in age
E) less massive

Question 27

Where on the H-R Diagram would we find stars that look red when seen through a telescope?

A) only near the top of the diagram and never near the bottom
B) only near the left side of the diagram and never near the right
C) only on the right side of the diagram and never on the left
D) only near the bottom of the diagram and never near the top
E) anywhere in the diagram

Question 28

Measurements show a certain star has a very high luminosity (100,000 x the Sun's) while its temperature is quite cool (3500^o K). How can this be?

A) it must be a main sequence star
B) it must be quite small in size
C) it must be quite large in size
D) it must be brown dwarf and not a regular star
E) this must be an error in observations; no such star can exist

Question 29

Astronomers identify the main sequence on the H-R diagram with what activity in the course of a star's life?

A) forming from a reservoir of cosmic material
B) fusing hydrogen into helium in their cores
C) letting go of a huge outer layer
D) dying
E) you can't fool me; so many stars are on the main sequence that there is no special stage in a star's life that can be identified with it