stars

Some objects in space just don't have what it takes to be a star. Which of the following is a "failed star", an object with too little mass to qualify as a star? a) A brown dwarf b) an M type dwarf c) any star with high proper motion d) the Sun e) An O-type star

a) A brown dwarf

Which law do astronomers use to determine the masses of the stars in a spectroscopic binary system? a) Kepler's 3rd Law b) Stefan-Boltzmann Law c) Wien's Law d) Hubble's Law

a) Kepler's 3rd Law

After a lot of work, a group of graduate students has finally measured the wavelengths of many dozens of lines in the spectrum of a distant star. If a number of the lines come from molecules such as titanium oxide, the star is likely to be which spectral type: (Hint: see table 17.2 in textbook) a) M b) B c) A d) we need more information; lines from molecules can be found in stars of every spectral type e) O

a) M

Which of the following has the smallest mass? a) a planet b) the sun c) the smallest mass star that can still have fusion of hydrogen to helium in its core d) you can't fool me, all the above have roughly the same mass e) a brown dwarf

a) a planet

Which of the following looks the brightest in the sky? a) a star with magnitude -1 b) a star with magnitude 1 c) a star with magnitude 6 d) a star with magnitude 10 e) you can't fool me, all of the above look equally bright from Earth

a) a star with magnitude -1

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 bottom (the horizontal axis) b) only on the main sequence c) H-R diagrams have nothing to say about spectral types d) along the right (vertical axis) e) only in the red giant region

a) along the bottom (the horizontal axis)

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 such very luminous stars are extremely rare, and thus any small neighborhood in the Galaxy is unlikely to contain one of them b) because such superstars only give off a lot of energy for a year or so, before they die c) because conditions in the "neighborhood" of the Sun only permit low-mass (low luminosity) stars to form d) 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 e) because all stars in the vicinity of the Sun have planets, and planets rob a star of its brightness

a) because such very luminous stars are extremely rare, and thus any small neighborhood in the Galaxy is unlikely to contain one of them

Astronomers identify the main sequence on the H-R diagram with what activity in the course of a star's life? a) fusing hydrogen into helium in their cores b) dying c) 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 d) forming from a reservoir of cosmic material e) letting go of a huge outer layer

a) fusing hydrogen into helium in their cores

Which of the following characteristics of a single star (one that moves through space alone) is it difficult to measure directly? a) its mass b) its apparent brightness c) its temperature d) its chemical composition e) you can't fool me, all of these are quite easy to measure directly

a) its mass

Stars on the main sequence obey a mass-luminosity relation. According to this relation, a) luminosity is proportional to mass to the fourth power (luminosity increases strongly with mass) b) bright stars have more mass around them in the form of planets, comets, and asteroids c) if you double the mass, you get double the luminosity d) the brightest stars are made of such light materials they hardly have any mass at all e) the lower the mass, the higher the luminosity

a) luminosity is proportional to mass to the fourth power (luminosity increases strongly with mass)

An exhausted-looking astronomer comes off the mountain where her observatory is located and tells you she has been doing photometry all night. What has she been up to? a) measuring the brightness of different stars b) putting the light of stars through a spectrograph to measure what elements are present c) counting the number of stars in different star clusters (groups) d) measuring the positions of stars on photographic plates taken over many years e) taking photos through bedroom windows in the valley below

a) measuring the brightness of different stars

Where on the H-R Diagram would we find stars that look red when seen through a telescope? a) only on the right side of the diagram and never on the left b) anywhere in the diagram c) only near the top of the diagram and never near the bottom d) only near the bottom of the diagram and never near the top e) only near the left side of the diagram and never near the right

a) only on the right side of the diagram and never on the left

A white dwarf, compared to a main sequence star with the same mass, would always be: a) smaller in diameter b) less massive c) larger in diameter d) the same size in diameter e) younger in age

a) smaller in diameter

Which of the following can astronomers NOT learn from studying the spectrum of a star? a) you can't fool me, all of the above can be learned from studying the spectrum b) whether it is rotating slow or fast c) whether it is a star the size of the Sun or a giant star d) its surface temperature e) its motion toward or away from us

a) you can't fool me, all of the above can be learned from studying the spectrum

The first astronomer who did photometry in a systematic way (even though he did not have a telescope) was a) Ptolemy b) Hipparchus c) Hubble d) Galileo e) Kepler

b) Hipparchus

A star that is quite hot and has a very small radius compared to most stars is called a) a main-sequence star b) a white dwarf c) an O-type star d) a red giant e) an M-type star

b) a white dwarf

Why are astronomers much more interested in the luminosity of a star than its apparent brightness? a) because the luminosity also tells us what elements the star is made of, while apparent brightness cannot tell us a star's chemical make-up b) because the luminosity tells us how bright a star really is, while apparent brightness only tells us how bright it happens to look from Earth c) you can't fool me, there is no difference between luminosity and apparent brightness; they are merely different terms for the same property of a star d) because luminosity can tell us how bright it is inside the star's core, while apparent brightness only tells us about its outside layers e) because luminosity can be measured exactly, but apparent brightness can only be roughly estimated

b) because the luminosity tells us how bright a star really is, while apparent brightness only tells us how bright it happens to look from Earth

Which color star is likely to be the hottest? a) red b) blue-violet c) yellow d) green e) oranges

b) blue-violet

Using a good pair of binoculars, you observe a section of the sky where there are stars of many different apparent brightnesses. You find one star that appears especially dim. This star looks dim because it is: a) very far away b) it could be more than one of the above; there is no way to tell which answer is right by just looking at the star c) very low luminosity d) partly obscured by a cloud e) radiating most of its energy in the infrared region of the spectrum

b) it could be more than one of the above; there is no way to tell which answer is right by just looking at the star

Astronomers call the motion of a star across the sky (perpendicular to our line of sight) its a) spectral type b) proper motion c) doppler shift d) light travel time e) radial velocity

b) proper motion

A graduate student has done a careful analysis of the spectrum of a star. While she has found lines from many elements, there was not a trace of the element helium in the spectra she has been analyzing. From this she can now conclude: a) there is most likely no helium anywhere in the star b) since helium shows lines only in hot stars, this star must be relatively cool c) since helium is the kind of element that quickly bonds with others, all the helium in this star must be in the form of molecules d) all the helium must be in the core of the star; there is none of it in the outer regions e) the student was not surprised, because NO star ever shows any lines of helium

b) since helium shows lines only in hot stars, this star must be relatively cool

An astronomer whose secret hobby is riding merry-go-rounds has dedicated his career to finding the stars that rotate the most rapidly. But the stars are all very far away, so none of them can be seen to spin even when he looks through the largest telescopes. How then can he identify the stars that rotate rapidly? a) all stars that rotate show a huge Doppler shift toward the blue end of the spectrum b) stars that rotate have much wider lines in their spectra than stars that do not c) this astronomer better spend some more time enjoying his hobby, because he is not doing well at his job; there is no way we know about today to identify stars that rotate d) stars that rotate have a significantly lower luminosity than stars that do not rotate e) stars that rotate bring the light atoms (like hydrogen) spinning up to their surfaces; so they can be identified by the elements they contain

b) stars that rotate have much wider lines in their spectra than stars that do not

An H-R Diagram plots the luminosity of stars against their: a) location in the sky b) surface temperature c) age d) diameter e) mass

b) surface temperature

Ninety percent of all stars (if plotted on an H-R diagram) would fall into a region astronomers call: a) the twilight zone b) the main sequence c) the supergiant region d) the visual region e) the white dwarf region

b) the main sequence

A star moving toward the Sun will show: a) more and more helium lines as it approaches us b) a significant increase in its apparent brightness (magnitude) c) a shift in the spectral lines toward the blue end (as compared to the laboratory positions of these lines) d) no change that can be measured with our present-day instruments e) a shift in the spectral lines toward the red end (as compared to the laboratory positions of these lines)

c) a shift in the spectral lines toward the blue end (as compared to the laboratory positions of these lines)

Which of the following statements about spectroscopic binary stars is FALSE? a) we can often use the changes in the positions of the spectral lines to measure the radial velocity of the stars in the system b) visually we can only see one star 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) 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

One key difference that astronomers use to distinguish between brown dwarfs and high-mass planets is that: a) brown dwarfs shine quite brightly in visible light, while planets are only visible from the light they reflect b) brown dwarfs have a much lower luminosity than any planets c) brown dwarfs are able to do deuterium fusion in their cores, while planets can't d) brown dwarfs are much lower in mass than planets like Jupiter e) brown dwarfs are all much larger in diameter than any planets

c) brown dwarfs are able to do deuterium fusion in their cores, while planets can't

At an astronomical conference, an astronomer gives a report on a star that interests astronomers because of hints that it may have a planet around it. In his report the astronomer gives the average speed with which this star is moving away from the Sun. How did the astronomer measure this speed? a) by seeing the whole star become much redder than it used to be b) by seeing how the luminosity of the star has been decreasing as it moves farther and farther away c) by looking at the Doppler shift in the lines of the star's spectrum d) the astronomer must be making up stories to impress his colleagues; there is no way to measure the speed with which stars move away or toward us. e) by measuring the diameter of the star (which is easy to do) and noticing that it is getting smaller and smaller

c) by looking at the Doppler shift in the lines of the star's spectrum

Astronomers arrange the stars into groups called spectral classes (or types) according to the kinds of lines they find in their spectra. These spectral classes are arranged in order of: a) increasing mass b) decreasing distance from us increasing amount of hydrogen c) decreasing surface temperature d) you can't fool me, there is no order to the spectral types (that's why the letters are not in alphabetical order)

c) decreasing surface temperature

When an astronomer rambles on and on about the luminosity of a star she is studying, she is talking about: a) the total amount of mass in the star b) what color the star is c) how much energy the star gives off each second d) the elements she can see in the star's spectrum e) the star's apparent size (the size seen from Earth)

c) how much energy the star gives off each second

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 middle of the main sequence, roughly where the Sun is b) in the upper left, among the bright main sequence stars c) in the lower right, among the least luminous main sequence stars d) in the upper right, among the supergiants e) in the lower left, among the white dwarfs

c) in the lower right, among the least luminous main sequence stars

Stars that lie in different places on the main sequence of the H-R diagram differ from each other mainly by having different: a) internal structure b) radial velocities c) masses d) compositions e) ways that they formed

c) masses

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) comparing the color of a star seen high above our heads and then again when it's near the horizon c) more than one of the above d) getting the light curve of an eclipsing binary star e) measuring the spectrum of a spectroscopic binary

c) more than one of the above

Why can astronomers not measure the diameters of stars directly? a) stars are all in binary systems, and we can only see the combined diameter of both stars 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 so bright, their light burns out all the delicate instruments we would use to measure their diameters e) you can't fool me; measuring the diameter of any star is a relatively easy process

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

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) none of the above c) that the lines in its spectrum show a blue-shift d) that the lines in its spectrum merge with the lines of the other star e) that it is no longer possible to learn what elements are in the star

c) that the lines in its spectrum show a blue-shift

Who was the astronomer who is the "H" in H-R diagram? a) Humason b) Hoyle c) Huggins d) Hertzsprung e) Hubble

d) Hertzsprung

Which of the following types of star is the coolest (has the lowest surface temperature)? a) F b) G c) A d) M e) O

d) M

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) red giants b) extras c) spectroscopic stars d) brown dwarfs e) main sequence stars

d) brown dwarfs

Studies of the spectra of stars have revealed that the element that makes up the majority of the stars (75% by mass) is a) stellarium b) helium c) carbon d) hydrogen

d) hydrogen

Two stars have the same luminosity, but star B is three times farther away from us than star A. Compared to star A, star B will look a) three times brighter b) just as bright as A c) nine times brighter d) nine times fainter e) three times fainter

d) nine times fainter

Two stars have the exact same luminosity, but star Y is four times dimmer looking that star X. This means that a) we can't figure out the relative distance of the two stars from the information given b) star Y is half as far away as star X c) star Y is four times as far away as star X d) star Y is twice as far away as star X e) star Y is 16 times as far away as star X

d) star Y is twice as far away as star X

When an astronomer measures a color index for a star, what is she measuring? (be careful here, this question is tricky) a) the amount of hydrogen in the atmosphere of the star b) the total luminosity of the star in all parts of the electromagnetic spectrum c) what color the human eye sees when people look at that star d) the difference between how bright a star looks at two different wavelength regions e) how the color of the star is changed when its light passes through the Earth's atmosphere

d) the difference between how bright a star looks at two different wavelength regions

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) actually, this is just an optical illusion; all stars are really the same brightness b) all the brightest stars are red, and red color is much easier to see against the black night sky c) we see them in crowded regions of stars, which give us the impression that the stars there are brighter than they really are d) these stars are intrinsically so luminous, that they can easily be seen even across great distances e) 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

In recent decades, astronomers discovered stars even cooler than the traditional spectral type M stars recently. Astronomers gave these cool stars a new spectral type, L. If you wanted to go out and find more such type L stars, what kind of instrument would it be smart to use? a) a swimming-pool size vat of commercial cleaning fluid, deep in an abandoned mine b) an x-ray telescope, in orbit above the Earth's atmosphere c) a CCD camera attached to an ultra-violet telescope d) a small visible-light telescope (something even an amateur astronomer or small college might have) e) a sensitive infra-red telescope

e) a sensitive infra-red telescope

One of your good friends 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) stars with low mass can be located anywhere at all in the H-R diagram c) among the stars at the top left of the main sequence d) among the supergiants e) among the stars at the bottom right of the main sequence

e) among the stars at the bottom right of the main sequence

A team of astronomers takes spectra of thousands of different stars in different parts of the sky. The spectra show significant differences. The main reason the spectra of the stars do not all look alike is that the stars a) sometimes have atmospheres and sometimes do not b) are located in many different regions of the Milky Way c) change their spectra as they age, and so young stars have very different spectra from older ones d) have different temperatures e) are made of significantly different elements

e) are made of significantly different elements

Imagine that a brilliant but quirky scientist in the biology department manages to put you in a deep freeze and you wake up in a million years. Which of the following statements about the sky you would see in that future time is correct? a) if you could see them up close, almost all the stars in the sky today will have changed their color significantly in a million years b) at the present time, astronomers do not know enough about the universe to say what the sky might be like in a million years c) all the stars we can see in the sky today will have died in a million years d) all the stars and constellations would look exactly the same as they do now e) because of proper motion, a number of the familiar constellations will look somewhat different in a million years

e) because of proper motion, a number of the familiar constellations will look somewhat different in a million years

Two stars that are physically associated (move together through space) are called a) double stars b) main sequence stars c) brown dwarf stars d) first contact stars e) binary stars

e) binary stars

For what type of star can astronomers measure the diameter with relative ease? (Pick best answer) a) main sequence stars b) visual double stars c) any star that is not a brown dwarf d) white dwarf stars e) eclipsing binary stars

e) eclipsing binary stars

Measurements show a certain star has a very high luminosity (100,000 x the Sun's) while its temperature is quite cool (3500o K). How can this be? a) it must be brown dwarf and not a regular star b) this must be an error in observations; no such star can exist c) it must be a main sequence star d) it must be quite small in size e) it must be quite large in size

e) it must be quite large in size

The most common kinds of stars in the Galaxy have a) diameters thousands of times greater than the Sun's b) enormous masses compared to the Sun c) a dozen or more stars in close orbit around them d) spectra that show they contain mostly carbon e) low luminosity compared to the Sun

e) low luminosity compared to the Sun