Quiz
Astronomy 180
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Questions in this quiz (180)
1The hydrogen in the outer layers of the Sun cannot undergo fusion because
- Athe temperature in the outer layers is too low to allow the hydrogen nuclei to come close enough together to undergo fusion.
- Bthe hydrogen in the outer layers is fundamentally different from the hydrogen in the core.
- Cthe hydrogen atoms in the surface layers are not ionized, as they are in the core, and ionization is one requirement for nuclear fusion.
- Dthe hydrogen in the outer layers is pure, and hydrogen must be mixed with helium, as it is in the core, in order to undergo fusion.
2Mira variables are not as useful as other variable stars in making astronomical calculations because.
- Atheir periods are too long to be measured easily..
- Bthere are relatively few of them..
- Ctheir periods are not always regular..
- Dno Mira variables are close enough for a parallax measurement
3How do astronomers know that globular clusters are old?.
- ATheir stars have a high abundance of heavy elements..
- BThey do not contain any red giant stars..
- CThere are no massive main-sequence stars in globular clusters..
- DThere are no main-sequence stars in globular clusters.,
4 Which factor, more than any other, modifies the evolutionary tracks of stars in binary combinations compared to their single star counterparts?
- Aradiation from one star heating the surface of the second star
- Btidal distortion of the shapes of the stars
- Cmass exchange between the stars
- Dreduction of the quantum mechanical limitation on continued shrinking of one star by the gravitational field of the second star
5A globular cluster is a group of stars that has
- Amany thousands of members, all very old, with very few elements heavier than helium.
- Bmany thousands of members, mostly binary, of different ages.
- Cmany thousands of members of different ages but with the same chemical composition
- Da few hundred members, often still embedded in the gas from which they were formed
6What is a Roche lobe?
- Ato that star
the imaginary boundary around each star in a close binary system which marks the limit outside of which planets cannot form - Bthe imaginary boundary around each star in a close binary system which marks the limit inside of which planets cannot form because they would be torn apart by the star's gravity
- Cthe imaginary boundary around each star in a close binary system which marks the limit of each star's gravitational pull; as long as each star is within its own Roche limit the stars will have no effect on each other
- Dthe imaginary boundary around each star in a close binary system encompassing the mass gravitationally bound to that star
- Ato that star
7In which phase of a star's life are thermonuclear reactions converting hydrogen into helium in the core of a star?
- Athe main-sequence phase
- Bthe horizontal branch phase
- Cas the star moves up the red giant branch for the first time
- Dthe protostar phase
8The helium flash is another name for
- Aa sudden onset of helium fusion reactions in the core of a low-mass red giant star.
- Ba sudden release of energy at the end of helium burning, due to core contraction.
- Cthe sudden appearance of helium during a supernova explosion (explosion of a star at the end of its life)
- Da sudden onset of helium fusion reactions in red giant and supergiant stars of any mass.
9The study of stars in clusters has helped astronomers to understand
- Athe reason for differences in surface temperatures of stars.
- Bstellar evolution—the development of stars with time.
- Cthe mechanism of mass loss in stars.
- Dthe action of nuclear fusion in stars.
10The end of the life of a red dwarf star is predicted to be a sphere of almost pure helium. But we have not detected any of these. What do we believe is the reason?
- AHelium is a relatively light material, so these helium spheres are expected to dissipate in a short time.
- BThere are very few red dwarfs, so their end products are expected to be rare.
- CThese helium stars are very dim and consequently hard to detect.
- DThe evolution rate for red dwarfs is so slow that none has yet evolved to its end stage.
11Stars are formed from interstellar matter. Why are stars in open clusters metal-rich, whereas stars in globular clusters are metal-poor?
- ASupernova explosions have blasted away the heavy elements in older globular cluster stars, leaving behind the metal-poor cores.
- BGlobular clusters have “burned” their heavy elements over their longer lifetime.
- COpen clusters are young, and stars have been formed from material in which stellar evolution and supernova explosions in earlier stars have enriched heavy metal concentrations steadily with time.
- DGlobular clusters have “burned” their heavy elements over their longer lifetime.
Globular cluster stars are so widely spaced, that they have not interacted and collided to produce the supernova explosions that generate metals.
12What “safety valve” operates in the gas of normal (nondegenerate) stars?
- AIf the stellar gas is suddenly heated, it will expand and cool.
- BIf the pressure gets too high, electrons will combine with protons to relieve the pressure.
- CIf the star gets too big, it will collapse into a black hole.
- DIf thermonuclear reactions proceed too quickly, the star will run out of fuel before anything drastic happens.
13Which of the following stars would you classify as a population II star?
- Aa star with a much higher abundance of heavy elements than the Sun
- Ba star with very low abundance of heavy elements
- Ca star with approximately the same abundance of heavy elements as the Sun
- Dany member of an open star cluster
14What is the minimum mass necessary in a protostar for it to begin nuclear reactions and become a main sequence star?
- A0.08 M?
- B1.0 M?
- C0.4 M?
- D1.4 M
15At which phase of a star's life will nuclear fusion reactions that convert helium into carbon and oxygen in the central core of a star occur?
- Aduring and immediately after the (first) red giant or supergiant stage
- Bin the red giant stage, before the helium flash
- Cduring the protostar stage, before the main sequence
- Dafter the main-sequence phase, before the star becomes a red giant
16Of the following astronomical objects or systems, which is likely to be the oldest?
- Aglobular cluster
- Bthe Sun
- Ca T Tauri star
- Dthe Pleiades
17What causes the core of a star to contract during the main-sequence phase of the star's life?
- AConvection in the outer layers carries energy out of the core more efficiently as the star ages.
- BThe rate of core hydrogen burning decreases as the hydrogen is used up, reducing the rate of energy generation.
- CHelium has a larger atomic weight than hydrogen and exerts a stronger gravitational pull on the core
- DThe conversion of hydrogen into helium reduces the number of particles in the core.
18What are the main general features that make clusters of stars useful to astronomers?
- AThe stars are at the same distance from Earth, were formed at approximately the same time, and were made from same chemical mix.
- BThe stars all have the same apparent magnitude, the same surface temperatures, and the same sizes.
- CThe stars all have the same intrinsic brightness but differ in size and surface temperature.
- DThe stars are all at the same distance from Earth, have the same surface temperature, and joined the cluster at various times.
19What is happening in the interior of a star that is on the main sequence on the Hertzsprung-Russell diagram?
- AThe star is generating internal energy by hydrogen fusion.
- BStars that have reached the main sequence have ceased nuclear “burning” and are simply cooling down by emitting radiation.
- CThe star is slowly shrinking as it slides down the main sequence from top left to bottom right.
- DThe star is generating energy by helium fusion, having stopped hydrogen “burning.”
20The main-sequence lifetime of a star with half the mass of the Sun
- Acould be longer or shorter than that of the Sun; it is not possible to tell from the information given.
- Bis longer than that of the Sun.
- Cis the same as that of the Sun, because mass does not affect the lifetime of a star.
- Dis shorter than that of the Sun.
21What scientific method is used to observe the pulsation in size of a Cepheid variable star?
- Aobservation of perturbations in the orbits of planets around these stars
- BThis behavior has only been predicted theoretically; it has never been detected
- Cobservation of the increase and decrease in the size of the star's image
- DDoppler shift of absorption lines in its spectrum
22What will be the diameter of the Sun when core helium burning begins?
- Aabout the size of Earth's orbit
- Bthe size of Earth
- Ctwice its present size
- Dhalf its present size
23When a protostar evolves to the point where it begins steady hydrogen fusion in its core and first achieves hydrostatic equilibrium, it is called
- Aa zero-age main sequence star.
- Ba T Tauri star.
- Ca proplyd.
- Da first-form main sequence star.
24Which of the following statements about the mass and lifetime of a star is true?
- AThe more massive the star, the faster it will evolve through its life.
- BThe less massive the star, the shorter its life, because it has less hydrogen “fuel” to burn.
- CThe mass of a star has no bearing on the length of a star's life or the speed of its evolution.
- DStars of about one solar mass have the shortest lives; less massive stars evolve slowly and live a longer time, whereas more massive stars have long lives because of the large amount of fuel they contain.
25After the helium flash in a low mass star
- Ahelium burning begins in the core and hydrogen burning ceases in the layers around the core.
- Bhelium burning begins in the core and hydrogen burning continues in the layers around the core.
- Call nuclear reactions cease.
- Dhelium burning ceases in the core but hydrogen burning continues in the layers around the core.
26What places a limit on the lifetime of a star?
- Aamount of available nuclear fuel it contains
- Bloss of the mass, and therefore of nuclear fuel, of the star into space by stellar winds
- Ccollisions between stars in a galaxy are sufficiently frequent that all stars will eventually be destroyed in this way.
- Dbuildup of spin as it evolves and contracts means that the star will eventually spin apart
27Degeneracy occurs when
- Aelectrons inside a star resist being pushed closer together than a certain limit.
- Bsolar wind particles ionize atoms in Earth's upper atmosphere.
- Cthermonuclear reactions halt the contraction of a protostar.
- Dmagnetic fields inhibit the motion of charged particles in sunspots.
28In a semidetached binary star system,
- Athe stars share the same outer atmosphere, but the cores of the two stars do not touch.
- Bboth stars fill their Roche lobes.
- Cone star fills its Roche lobe, while the other does not.
- Done star orbits the center of mass, while the other moves freely through space.
29The Hertzsprung-Russell diagram of a globular cluster does not contain any stars with high luminosity and high temperature on the main sequence because
- Athis type of cluster contains only low-mass stars and has never had such stars on its main sequence.
- Bthe stars that were in this position on the main sequence have undergone the usual splitting into binary stars, and hence appear lower down on the diagram.
- Cthese high-mass stars evolved away from the main sequence long ago.
- Dstars that will occupy this position on the main sequence have not yet evolved there from the protostar stage.
30If you make a list of the 100 brightest stars in the sky you will find that most of them are
- Agiants and supergiants.
- Bwhite dwarfs.
- Cbrown dwarfs.
- Dmain sequence stars
31What makes a red giant star so large?
- AThe hydrogen-burning shell is heating the envelope and making it expand.
- BThe star has many times more mass than the Sun.
- CThe helium-rich core has expanded, pushing the outer layers of the star outward.
- DRed giants are rapid rotators, and centrifugal force pushes the surface of the star outward.
32What kind of star is our Sun?
- Ametal rich Population I
- Bmetal poor Population I
- Cmetal poor Population II
- Dnone of these
33The 12C and 16O, which now form part of living matter, were part of the cold, dark nebula from which the Sun formed. How did they get there?
- AThey were formed in an earlier supernova explosion and dissipated through space.
- BThey were formed by earlier generations of stars while they were on the main sequence.
- CThey were part of the original Big Bang and thus part of everything formed since then.
- DThey were formed by earlier generations of stars while they were in their red giant phase.
34How long is the lifetime of a star with three times the Sun's mass compared to the lifetime of the Sun? (See Table 19-1, Freedman and Kaufmann, Universe, 10th ed.)
- Aabout 1/3 as long
- Babout 1/500 as long
- Cabout 1/15 as long
- Dabout 3 times as long
35The age of a cluster can be found by
- Ameasuring its speed of motion relative to the Sun.
- Bdetermining the turnoff point on the main sequence of its HR diagram.
- Ccarrying out a number count of the stars in the cluster.
- Dobserving its position in the sky with respect to the Sun.
36The temperature at which thermonuclear reactions begin to convert helium into carbon (helium burning) is
- A100 million K.
- B15 million K.
- C1 million K.
- D1 billion K.
37What is a Cepheid variable star?
- Aa high-mass star that pulsates regularly in brightness
- Ba star that normally remains constant in brightness but occasionally flares up in brightness by several magnitudes
- Cone of several classes of stars that pulsate randomly in brightness
- Da low-mass, horizontal-branch star that pulsates regularly in brightness
38The Pauli exclusion principle, describing the quantum states of particles, stipulates that no two identical particles (such as electrons) can have the same
- Abe in the same quantum state.
- Bhave the same speed.
- Chave the same electrical charge.
- Dhave the same position in space.
39What unusual process is involved in the helium flash?
- AAn increase in temperature causes an increase in the nuclear reaction rate but has no effect on pressure.
- BAn increase in the nuclear reaction rate causes an increase in the temperature and the pressure.
- CAn increase in temperature causes an increase in the pressure with no increase in the nuclear reaction rate
- DAn increase in the pressure causes a decrease in the temperature and the nuclear reaction rate.
40The event which marks the end of the main sequence lifetime of a star is
- Athe helium flash.
- Bthe formation of a nova.
- Cthe end of hydrogen fusion in the core.
- Dthe formation of a planetary nebula.
41Stars in a binary system are useful in studying mass transfers because we know the two stars have the same
- Aradius
- Bspectral type
- Cage
- Dmass
42If you were to look at one kilogram of material taken from the surface of the Sun and 1 kilogram taken from the center, which of the following statements would be true of these two 1 kilogram masses?
- ANeither of them would contain any hydrogen.
- BThe kilogram from the surface would contain less hydrogen than the one from the center.
- CThe kilogram from the surface would contain more hydrogen than the one from the center.
- DThey both would contain the same amount of hydrogen.
43If you make a list of the 100 nearest stars in the sky you will find that most of them are
- Abrown dwarfs.
- Bgiants and supergiants.
- Cwhite dwarfs.
- Dmain sequence stars.
44In the helium burning stage of a star's later life, the major chemical element produced in this process is
- Athe light isotope of helium—3He.
- Bcarbon—12C.
- Cberyllium—8Be.
- Dheavy hydrogen—2H.
45The evolution of a star is controlled mostly by its
- Ainitial mass.
- Bsurface temperature.
- Clocation in the galaxy.
- Dchemical composition.
46In comparing a young red giant star to the main sequence star from which it evolved, three of the following statements are true. Which one is not true?
- AThe red giant star has the cooler surface temperature.
- BThe core of the main sequence star is hotter.
- CThe red giant star has a larger diameter.
- DHydrogen fusion occurs in the core of the main sequence star and in a shell around the core in the red giant star.
47What would you expect to be the overall color of a globular cluster of stars?
- Ared, because of the older population of stars in the cluster
- Bblue, because of the scattering of starlight from the dust surrounding the stars in the cluster
- Cred, because of the emission of light by the hydrogen gas surrounding the stars in the cluster
- Dblue, because of the contribution from young and very hot stars in the cluster
48What is a red giant?
- Aa large emission nebula
- Ba large, red star burning hydrogen into helium in its cor
- Ca star burning hydrogen into helium in a shell around the core
- Da protostar in the “upper right” part of the Hertzsprung-Russell diagram
49What is the expected main-sequence lifetime of a star with a mass of 15 solar masses?
- A3 million years
- Bless than 1 million years
- C10 billion years
- D15 million years
50RR-Lyrae stars are
- Aeclipsing binary stars.
- Bpulsating stars that vary irregularly, all with periods of several hundred days.
- Cpulsating stars that vary regularly, all with periods of less than one day.
- Dpulsars, with very rapid and regular brightness fluctuations caused by rapid rotation of stars with active regions on their surfaces.
51A star with an apparent magnitude of m = + 2.5 is at 100 pc from Earth. What is its absolute magnitude, M?
- A–7.5
- B+7.5
- C–2.5
- D–47.5
52The point around which two stars of unequal mass in a binary system appear to revolve is
- Aclosest to the more massive star.
- Bhalfway between the two star centers
- Cat the center of the more massive star.
- Dclosest to the less massive star.
53The absolute magnitude of the Sun is +4.8 and its luminosity is 3.9 × 10^26 watts. The luminosity of a star whose absolute magnitude is +3.8 is
- A1.6 × 10^26 watts.
- B3.9 × 10^27 watts.
- C9.8 × 10^26 watts
- D2.9 × 10^26 watts.
54Suppose 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?
- A1/25 as bright
- B1/5 as bright
- C1/20 as bright
- D1/2.2 as bright
55What condition is necessary for us to see eclipses of stars in binary star systems?
- AThe line of sight from Earth to the star system must be very close to the perpendicular to the orbital plane of the stars.
- BThe stars must have very similar surface temperatures whatever the inclination of their orbital plane to the line of sight, for us to see a significant eclipse.
- COne of the stars must be much bigger than the other so that it can hide its smaller companion when the orbital plane is at a large angle to the line of sight.
- DThe line of sight from Earth to the star system must be in or very close to the orbital plane of the stars.
56The star Bellatrix in Orion looks bluish to the naked eye. Why is this?
- ABellatrix is made of blue material.
- BThe spectrum of light emitted from Bellatrix peaks in the blue region of the spectrum, and in fact, almost all of its light is concentrated in the blue region of the spectrum.
- CThe spectrum of light emitted from Bellatrix peaks in the ultraviolet region of the spectrum. Within the visible part of the spectrum, there is more emission in the blue than in any other color.
- DBellatrix is moving toward us rapidly enough that its light is appreciably blueshifted.
57Suppose that, at night, the brightness of a light bulb is measured from a certain distance and then the light bulb is moved to a distance twice as far away. How bright will the light appear compared to the earlier measurement?
- A1/8 as bright
- B1/16 as bright
- C1/4 as bright
- D1/2 as bright
58A star of spectral class L is
- Aa red star, intermediate between spectral classes K and M
- Bnot a star at all, but a brown dwarf.
- Ca yellow star like the Sun.
- Dnot a star at all, but a white dwarf.
59Luminosity is measured in
- AWatts per square meter.
- BJoules per second.
- Cparsecs.
- Darcseconds per year.
60Parallax is the
- Ashift in position of an object as it moves.
- Bapparent shift in position of a nearby object as we move.
- Cangle subtended by an object, as seen by us.
- Ddistance to an object, measured in parsecs.
61All of the statements comparing the Sun to the Giant stars are true except which of the following?
- AThe Giant stars are more luminous than the Sun.
- BThe Giant stars are larger than the Sun.
- CThe Giant stars have smaller absolute magnitudes than the Sun.
- DThe Giant stars are hotter than the Sun.
62Where on the Hertzsprung-Russell diagram do most local stars in our universe congregate?
- An the white dwarf area, the “graveyard” of stars
- Bin the supergiant area, where the most massive stars spend a significant time
- Con the main sequence where stars are generating energy by fusion reactions
- Din the giants area, where most stars spend the longest time of their lives
63What is the relationship between stellar parallax (p) measured in seconds of arc and distance (d) measured in parsecs?
- Ap = 1/d
- Bd = 2 p
- C1/d = 2 p
- Dd = p
64The luminosity of a star is
- Aits brightness at a hypothetical distance of 10 parsecs (32.6 light-years) from Earth.
- BAnother name for its color or surface temperature.
- CIts total energy output into all space over all wavelengths.
- Dits brightness as seen by people on Earth.
65If 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?
- A500 pc
- B100 pc
- C200 pc
- D0.01 pc
66Stellar parallax is the
- Aelliptical motion of a star in a binary system, as the two stars orbit around each other.
- Bapparent shift in the position of a nearby star because of Earth's motion.
- Cassumed change in the distance to a star when it dims, as it passes through an interstellar cloud.
- Difference between the apparent magnitude and the absolute magnitude of a star.
67If Star A has an apparent magnitude of +5, and Star B has an apparent magnitude of +10, then
- AStar B is 100 times as bright as Star A.
- BStar A is 100 times as bright as Star B.
- CStar B is twice as bright as Star A.
- DStar A is twice as bright as Star B.
68If the Hipparchos satellite measures the parallax motion of a star against the background stars and concludes that the star has a parallax of 0.004 arcseconds, how far is that star from Earth?
- A25 pc or 81 ly
- B250 pc or 800 ly
- C0.004 pc or 0.013 ly
- D400 pc or 1300 ly
69In a particular binary star system, only one star is visible because the other star is too faint to see at that distance. An astronomer measures the size (semimajor axis) and period of the orbit of the visible star. From this information the astronomer can calculate
- Athe sum of the masses of the two stars but not the mass of each star separately.
- Bthe mass of each star.
- Cthe mass of the visible star but not that of the unseen star.
- Dnothing about the mass—both stars have to be visible to do so.
70 On the basis of the graph of absorption line strengths in spectra of stars presented, what is the spectral type of a star with the following spectral pattern: very strong H, weaker Mg II and Si II, and no He I or Ca II lines?
- AG
- BA
- CB
- DK
71A white dwarf is
- Aany main sequence star with a surface temperature between about 9000 K and 15,000 K.
- Ban object intermediate between planets and stars, that will never become a star.
- Ca star at the end of its life, with a size close to that of Earth.
- Da star at the beginning of its life, with a size two to ten times that of the Sun.
72An eclipsing binary system is
- Aa star that is periodically eclipsed by the Moon.
- Btwo stars that are clearly seen as separate but associated in the sky.
- Ctwo stars whose combined light output when measured from Earth appears to vary periodically as the two stars move in front of one another.
- Dtwo stars whose spectral lines move back and forth, indicating relative motion.
73In the spectral sequence of star types, each category has been divided into ten intervals. The Sun is classified as
- AG2.
- BM9.
- CA1.
- DO1.
74A particular star has a radius half that of the Sun and a luminosity equal to 60% of that of the Sun. What is the star's surface temperature? The surface temperature of the Sun is 5800 K.
- A7220 K
- B6650 K
- C3610 K
- D4660 K
75Where are brown dwarfs located on the HR diagram?
- Aupper right
- Bupper left
- Clower left
- Dlower right
76Absorption lines in the spectra of some binary stars are seen to change periodically from single to double lines and back again. Why is this?
- AOscillations on the surfaces of the stars leads to Doppler-shifted lines.
- BMotion toward and away from Earth during their orbital motion results in Doppler shift of light from these stars at times and no shift when the stars are moving perpendicular to the line of sight.
- CThe effect of the gravitational field of one star on the atoms of the second star produces spectral line shifts periodically.
- DPeriodically, the magnetic field of one star produces Zeeman splitting of spectral lines in atoms of the second star.
77Star A has a luminosity LA = 100 LSUN and it is 1000 pc away. Star B has the same luminosity as the Sun, LSUN, and it is 100 pc away. What can you say about the brightnesses of these two stars?
- AStar A and Star B have the same brightness.
- BStar A is brighter than Star B.
- CIt is not possible to determine the answer without knowing LSUN, the luminosity of the Sun.
- DStar B is brighter than Star A.
78What 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?
- AIt is fainter.
- BThere are no stars in the upper right part of the diagram.
- CIt is larger.
- DIt is hotter.
79Two 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?
- AThe hotter star has a quarter the radius of the cooler star.
- BNothing can be determined about the radii from this information.
- CThe cooler star has half the radius of the hotter star.
- DThe hotter star has half the radius of the cooler star.
80The relationship between the luminosity of a star, L, its surface temperature, T, and its radius, R, is given (with s = Stefan-Boltzmann constant) by
- AL = 4psRT^2.
- BL = 4psR^2T^4.
- CL = 4psR^4T^2.
- DL = 4psR^2T^2.
81The relationship between mass and luminosity of stars on the main sequence is that
- Athe greater the stellar mass, the less the luminosity.
- Bthe luminosity of stars rises to a peak at around a mass of 1 solar mass and decreases as mass increases beyond this limit.
- CThe greater the stellar mass, the larger the luminosity.
- Dluminosity is independent of the stellar mass.
82If you compare two stars,
- Athe one with the larger radius must have the greater luminosity.
- Bthe one with the higher surface temperature must have the greater luminosity.
- CThe one with the smaller absolute magnitude must have the greater luminosity.
- Dthe one with the larger surface area has the greater energy flux from its surface
83The absolute magnitude of a star is the brightness the star would appear to have if it were placed at what distance from Earth?
- A32.6 ly
- B10 ly
- C1 AU
- Dthe distance to the galactic center
84A star whose ratio of visual and blue apparent brightnesses is bV/bB = 5 (see Figure 17-9, Section 17-4, Freedman and Kaufmann, Universe, 10th ed.) has a surface temperature of
- AIt is not possible to determine the star's temperature with this information alone, because the value of either bV or bB is also needed.
- B3000 K.
- C12,000 K.
- D6000 K.
85Which of the following four spectral classifications represents the coolest stellar surface temperature?
- AK
- BA
- CG
- DB
86How bright is a magnitude +3.0 star compared to a magnitude +4.0 star?
- A4/3 (1.333) times brighter
- B10 times brighter
- C2.512 times brighter
- D1/2.512 times as bright
87The radial-velocity curve of a star in a binary star system is a plot against time of the
- Aposition of the star in celestial coordinates.
- BTemperature of the star as determined from the movement of the peak wavelength of its spectrum.
- Cspeed of the star in a direction perpendicular to the line of sight to the star.
- Dvariation of Doppler shift of its spectral lines and hence of its speed toward or away from us.
88How do two stars in a binary system orbit each other?
- AThey both move on the same elliptical orbit around one of its foci.
- BThey both follow elliptical orbits around a common point between the stars.
- CThe lower mass star orbits in an ellipse around the center of the larger mass star.
- DThe larger mass star orbits around the center of the smaller mass star.
89The technique called photometry in stellar astronomy is the measurement o
- Athe arrival times of photons from variable and pulsating stars, to determine accurately the pulsation or rotation periods of these stars.
- Bthe relative absorption of light by different atoms and molecules in high resolution spectra of starlight, from which stellar temperatures can be estimated.
- Cthe precise positions and relative motions of stars in the galaxy, from which galactic structure and overall rotation can be determined.
- Dthe intensity of light from stars through several limited-bandpass filters from which surface temperature, variability, luminosity, etc. of stars can be determined.
90If a nearby star shows a parallax of 0.5 arcseconds when Earth moves through 1 AU, at what distance is it from Earth in light-years?
- A2 ly
- B6.52 ly
- C1.83 ly
- D3.26 ly
91Which of the following spectral classifications of stars is in correct order of increasing temperature?
- AMKGFABO
- BABFGKMO
- COBAFGKM
- DKMGFABO
92The star Elnath is classified as B7 III, and the star Al Na'ir is classified as B7 IV. This tells us that compared to Al Na'ir, Elnath is
- Aabout the same intrinsic brightness, but considerably hotter.
- Babout the same intrinsic brightness, but considerably cooler.
- Cabout the same temperature, but intrinsically much brighter.
- Dabout the same temperature, but intrinsically much fainter.
93Proper motion of a star is defined as its
- Aapparent motion against the background stars as a consequence of Earth's orbital motion around the Sun.
- Breal motion in three-dimensional space.
- Capparent motion toward or away from us, measured by the Doppler shift of its spectral lines.
- Dapparent motion across our sky against the background stars.
94What is the physical reason that astronomers can find the luminosity class (I, II, III, IV, or V) of a star using the star's spectrum?
- AThe absorption lines in the spectrum are affected by the star's surface temperature.
- BThe relative amounts of hydrogen, helium, and other elements are different for stars of different luminosity classes.
- CThe absorption lines in the spectrum are affected by the density and pressure of the star's atmosphere.
- DThe wavelength of maximum emission (given by Wien's law) is affected by the size of the star.
95 Capella is 180 times more luminous than the Sun, whereas Aldebaran is 370 times more luminous than the Sun. Capella has an apparent brightness of 3.5 × 10^–8 Watts/m^2. How far away is Aldebaran compared to Capella?
- AAldebaran is 0.65 times as far away as Capella.
- BAldebaran is 2.4 times as far away as Capella.
- CAldebaran is 1.55 times as far away as Capella.
- DAldebaran is 0.42 times as far away as Capella.
96What proportion of visible stars in the night sky are multiple-star systems?
- Aabout 50%, or 1/2
- Bnearly 100%
- Cabout 25%, or 1/4
- Dless than 1%
97On the basis of the graph of absorption line strengths, what is the spectral type of a star with the following spectral pattern: very strong He I lines, moderately strong H lines, weak Si III lines, and no Ca II, Fe II, or He II lines?
- AF
- BB
- CA
- DM
98A particular star in a binary star system orbits the other in an elliptical orbit with a semimajor axis of 3 AU and a period of 5 years. What is the sum of the masses of the two stars in the system?
- A0.9 M.
- B13.9 M.
- C1.1 M.
- D0.07 M.
99Where do we find the most massive stars on the main sequence in a Hertzsprung-Russell diagram?
- Aupper left
- Blower right
- Ccenter, with lower mass stars on either side
- DThey all have approximately the same mass, because this is what defines the main sequence.
100Spectroscopic parallax is the
- Achange 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.
- Bapparent change in position of a nearby star compared to distant background stars, due to the motion of Earth around the Sun.
- Cdistance to a star measured using the spectral-luminosity class of the star and the inverse square law.
- Dapparent 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.
101Why is there a limited range of stellar surface temperatures around 10,000 K, at which neutral hydrogen gas absorbs visible light in the Balmer series?
- AThere must be sufficient continuum radiation from the stellar surface in the visible region to be absorbed by the hydrogen gas.
- BThere must be electrons at the n = 3 energy level for Balmer absorption to occur. If the gas is too cold, electrons are only in the n = 1 and 2 levels, whereas if the gas is too hot, the gas is ionized, and no electrons are left in the hydrogen atoms.
- CElectrons in hydrogen have to be at the n = 2 energy level to produce absorption in this series. If the gas is too cold, most atoms are in the n = 1 state, and if it is too hot, most atoms are ionized.
- DElectrons must be in the ground state n = 1 to undergo Balmer absorption. If the gas is too cold, electrons cannot be excited from this level, whereas if it is too hot, there are no electrons left in the n = 1 level.
102In the Hertzsprung-Russell diagram of Fig. 17-15a of Freedman and Kaufmann, Universe, 10th ed., which of the following is the correct sequence of stars in order of increasing intrinsic brightness?
- AProcyon B, Sirius B, the Sun, Deneb
- BDeneb, the Sun, Sirius B, Procyon B
- CThe Sun, Procyon B, Deneb, Sirius B
- DSirius B, Deneb, Procyon B, the Sun
103 Two stars have the same spectral classification, say M2, but one of them is a Red Giant while the other is a Main Sequence star. To determine which is which, we look at their spectra because
- Athe absorption lines in the Giant will be narrower because of the temperature difference between the two luminosity classes.
- Bthe absorption lines in the Giant will be narrower because of the pressure broadening effect.
- Che absorption lines in the Giant will be broader because of the temperature difference between the two luminosity classes.
- Dthe absorption lines in the Giant will be broader because of the pressure broadening effect.
104In 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
- Anothing else.
- Bthe star's spectrum.
- Cthe star's luminosity (total energy output per second).
- Dthe star's surface temperature.
105The spectrum of an ordinary main sequence star is a
- Acontinuum of colors crossed by brighter lines caused by emission of hot atoms and molecules on the surface.
- Bsmooth continuum of color, peaking at a specific wavelength whose position is dependent on the surface temperature.
- Cseries of emission lines, mostly from hydrogen, the major constituent of stellar surfaces, that occasionally overlap to produce sections of continuous color.
- Dcontinuum of colors crossed by dark absorption lines, caused by absorption of cooler atoms and molecules at the surface.
106Which of the following observations would not be an indication of a binary star system?
- Aspectral lines from the “star” appearing to move back and forth periodically in position
- Bobservation of the “star” image separating into two distinct images periodically
- Cmotion of the “star” in a straight line against the background field of stars
- DThe “star” appears to become periodically dimmer for a few hours at a time.
107A particular star is at a distance of 20 pc from Earth. For this star, the apparent magnitude would be
- Aa smaller number than the absolute magnitude.
- Ba larger number than the absolute magnitude.
- Cthe same as the absolute magnitude, because magnitude is independent of distance.
- Deither larger or smaller than the absolute magnitude, depending on the temperature and diameter of the star.
108Which of the following atoms or ions will produce the strongest absorption lines in the spectra of stars with the highest surface temperatures?
- AFe I, neutral iron
- BHe II, ionized helium
- CH I, neutral hydrogen
- DCa II, singly ionized calcium
109The spectral type of a star is most directly related to (and determines uniquely) its
- Asurface temperature.
- Babsolute magnitude.
- Cluminosity.
- Dsize or radius.
110The spectral-luminosity class of the star a Arae is B2 V, and that of p Herculi is K3 II. Using ONLY this information and not looking anything up in tables or diagrams, we know for sure
- Aonly that a Arae is hotter than p Herculi.
- Bthat a Arae is hotter but intrinsically fainter than p Herculi.
- Cthat a Arae is cooler and intrinsically fainter than p Herculi.
- Donly that a Arae is cooler than p Herculi.
111The absolute magnitude of the Sun is +4.8 and its luminosity is 3.9 × 10^26 watts. The absolute magnitude of the star ? (Nu) Hydrae is –0.What is the luminosity of ? Hydrae?
- A7.8 × 10^25 watts
- B2.0 × 10^27 watts
- C3.9 × 10^28 watts
- D3.9 × 10^24 watts
112Two 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
- Amust be at the same distance away from us.
- Bmust have the same temperature.
- Cmay be at different distances, in which case the farther one must have the greater luminosity.
- Dmay be at different distances, in which case the nearest one must have the greater luminosity.
113What is the color of a star whose ratio of visual and blue apparent brightnesses, bV/bB, is 1.8?
- Ablue-white
- Byellow-white, similar to that of the Sun
- Cred
- Dwhite
114We can tell that some stars are relatively close to us in the sky because
- Athey are occasionally occulted or eclipsed by our Moon.
- Bthe light from these stars shows only a very small redshift caused by the universal expansion of the universe.
- Cthey appear to move periodically back and forth against the background stars because of Earth's movement around the Sun.
- Dthey appear to be extremely bright.
115The Hertzsprung-Russell diagram is a statistical plot of which of the following two stellar parameters?
- Amass and surface temperature
- Bluminosity and mass
- Cluminosity and surface temperature
- Dradius and mass
116Apparent magnitude is a measure of the
- Atemperature of a star.
- Bbrightness of a star, as seen from Earth.
- Csize (diameter) of a star.
- Dintrinsic brightness (actual light output) of a star.
117An astronomer plots the H-R diagram of a star cluster and finds that it contains hot B-type stars on the main sequence and cooler G- and K-type stars noticeably above the main sequence. This cluster is
- Aold, because the G and K stars are already evolving off (away from) the main sequence.
- Bimpossible, because one cannot have cool stars above the main sequence when hotter stars are on the main sequence.
- Cvery young, because the G and K stars are still evolving toward the main sequence.
- Dof indeterminate age, because one cannot estimate the age of the cluster from the information given.
118What is happening in a star that is on the main sequence on the Hertzsprung-Russell diagram?
- AThe star is generating internal energy by hydrogen fusion, creating helium.
- BThe star is slowly shrinking and heating up as it slides up the main sequence from bottom right to top left in the H-R diagram.
- CThe star is generating internal energy by helium fusion, creating carbon.
- DNuclear reactions have ceased, and the star is simply cooling down.
119Evidence for the interstellar medium has been provided by all of the following except one. Which is the exception?
- Aunshifted spectral lines observed when examining a binary star system
- Bthe neutrino flux
- Cinterstellar reddening
- Dthe existence of interstellar clouds like the Horsehead Nebula in Orion
120How large was the Sun when it first formed as a protostar, perhaps 1000 years after formation?
- Aabout 100 times its present diameter
- Babout 1000 times its present diameter
- Cabout 20 times its present diameter
- Dthe same diameter as it is now
121A particular giant molecular cloud has a mass of 400,000 solar masses. What is the mass of helium in this cloud?
- A300,000 solar masses
- B100,000 solar masses
- C392,000 solar masses
- D4000 solar masses
122Astronomers use the symbol H II to mean
- Aneutral hydrogen.
- Bionized hydrogen.
- Cmolecular hydrogen (with two atoms)
- Ddeuterium (hydrogen with a nucleus of two particles: one neutron and one proton)
123How can an O-type star trigger the formation of other stars? Three of the following statements are correct, and one is incorrect. Which is incorrect?
- AThe shock wave produced when an O-type star forms a supernova can compress the ISM and cause it to collapse.
- BO-type stars are massive. When they form stellar nebulae, as the Sun did, small stars form instead of planets
- CO-type stars are massive and thus have short lifetimes. After such a star erupts in a supernova, the material it ejects into space can eventually condense to form a new generation of stars.
- DThe H II region surrounding an O-type star expands into the giant molecular cloud, producing a shock wave which can compress the un-ionized material and cause it to collapse.
124A brown dwarf is
- Aa general name for objects similar to the planet Jupiter.
- Ba star of less than about 1.5 solar masses at the very end of its life, after it has cooled to near-invisibility.
- Cany star whose blackbody spectrum peaks in the brown region of the visible spectrum.
- Dan object intermediate between a planet and a star, with not enough mass to begin nuclear reactions in its core.
125How does a massive star normally end its life?
- AIt explodes.
- BIt collapses inward, and the whole star becomes a black hole.
- CIt gradually shrinks to the size of Earth.
- DWe don't know, because its lifetime is longer than the age of the universe.
126The ionization energy of hydrogen is 13.6 electron volts or 2.8 × 10^–18 Joules. A photon emitted from a hot O or B star can ionize hydrogen if it has a wavelength no greater than
- A2.18 × 10^–18 meters.
- B9.12 × 10^–8 meters.
- C5.69 × 10^–11 meters
- D6.54 × 10^–10 meters.
127The space between stars is now known to contain
- Agas, made up of atoms, molecules, and dust particles.
- Blarge quantities of dust that absorb light but no gas, either atomic or molecular.
- Ca perfect vacuum.
- Dvariable amounts of gas but no dust, because dust forms only in planetary systems near stars.
128What is the predominant atomic or molecular mechanism that produces the light we see from emission nebulae?
- AUV light from hot stars ionizes atoms, and the subsequent recombination of electrons with these ions produces spectral lines.
- BPhotons of UV and X radiation from very hot embedded stars accelerate electrons by collision and these accelerating electrons radiate at all wavelengths.
- CRadio energy from embedded stars excites atoms to high atomic states, and spectral lines are produced as these atoms return to their unexcited states.
- DRadiation from nearby stars heats the gas, and the gas then emits a continuum spectrum appropriate to its temperature.
129A protostar of about 1 solar mass is gradually contracting and becoming hotter. This will cause its position on the Hertzsprung-Russell diagram to shift slowly
- Adownward and toward the right.
- Bupward and toward the left.
- Cupward and toward the right.
- Ddownward and toward the left.
130A reflection nebula is made visible by
- Alight from embedded stars reflected over a wide range of wavelengths toward Earth, by crystals of water, methane, and ammonia ices.
- Bblue light, preferentially scattered by tiny dust grains.
- Cthermal energy emitted as a continuous spectrum by very hot gas, much like that emitted by a hot body on Earth.
- Demission lines from hydrogen, which itself has been ionized by UV light from embedded stars.
131What prevents a star from having a mass greater than about 200 solar masses?
- AGas pressure becomes so high as a consequence of high temperatures, that the excess mass is pushed back into space.
- BA star of larger mass would collapse under its own gravity, and the whole star would become a black hole
- CThe core of a larger-mass star would evolve rapidly and explode before the overall star finished contracting as a protostar.
- DNo interstellar clouds are found that contain more than 200 solar masses.
132What are the dimensions of a typical dark nebula of gas and dust within which a star might form?
- Aabout 10 solar masses inside a diameter of about 10 parsecs
- B1 or 2 solar masses inside a diameter of about 100 AU, about the size of the solar system
- Ca few thousand solar masses inside a diameter of about 10 parsecs, or about 30 light-years
- Da few thousand solar masses inside about 1 AU, Earth's orbit
133When plotted on an H-R diagram, a particular star cluster has its more massive stars on the main sequence and its less massive stars above the main sequence. Can we find the age of this cluster (i.e., how long it is since its stars condensed from the interstellar medium)?
- AYes, by finding the least massive star on the main sequence. The age of the cluster equals the time that this star spent as a protostar.
- BYes, by finding the most massive star on the main sequence. The age of the cluster equals the time that this star spent as a protostar.
- CYes, by finding the least massive protostar. The age of the cluster equals the time that this star takes to reach the main sequence.
- DNo
134What is the ultimate fate of an open star cluster?
- AThe stars in it escape one by one until the cluster no longer exists.
- BThe shape of the cluster remains more or less as it is now while the stars in it age and die
- COver time the stars in it collide and merge, eventually creating a black hole.
- DThe stars in it gradually sink toward the center, creating a globular cluster.
135What is the most important factor that determines the point in the Hertzsprung-Russell diagram where a protostar reaches the main sequence?
- Athe size of the interstellar cloud from which the protostar formed
- Bthe mass of the protostar
- Cthe initial luminosity of the protostar
- Dthe initial temperature of the protostar
136Where would you look to find a newly forming star?
- Ainside a black hole
- Ba planetary nebula
- Ca globular cluster
- Dan open cluster
137Where are protostars most likely to form?
- Aemission nebulae
- Bdark nebulae
- Cplanetary nebulae
- Dreflection nebulae
138In the magnetic model for the bipolar outflow from a protostar
- Amagnetic field lines through the circumstellar accretion disk become twisted and concentrated by the rotation of this disk.
- Bmagnetic field lines emanate from the poles of the protostar and carry material outward from the stellar interior.
- Cmagnetic field lines associated with the galaxy as a whole are concentrated and shaped by their interaction with the magnetosphere of the protostar.
- Dthe jets are formed along magnetic field lines, which go from the north magnetic pole of one protostar to the south magnetic pole of a second protostar which forms a close binary pair with the first.
139It is believed that protoplanetary disks form around
- Astars of small and intermediate size, with masses below about 3 solar masses
- Bonly the most massive stars, with masses above about 4 solar masses
- Conly the smallest stars with masses below about 0.4 solar masses.
- Dall stars.
140Which is the second most abundant element in the universe (after hydrogen)?
- Anitrogen
- Bhelium
- Ccarbon
- Diron
141The source of a protostar's heat is
- Agravitational energy, released as the protostar expands.
- Bgravitational energy, released as the star contracts.
- Cnuclear reactions converting helium to carbon and oxygen in its core.
- Dnuclear reactions converting hydrogen into helium in its core.
142How have molecules such as formaldehyde (H2CO) been detected in interstellar clouds?
- Aby observing the chemical reactions in which they are created
- Bby direct sampling by space probes
- Cby molecular emission lines
- Donly by theoretical modeling, knowing that the component elements (H, C, O) are present
143What occurrence defines the end of the protostar phase of a star's life and the start of the main-sequence phase?
- AThe star stops accreting mass from the interstellar cloud.
- BConvection begins in its interior.
- CThe star begins to expand to become a red supergiant.
- DThe nuclear reactions in its core allow it to gain hydrostatic equilibrium.
144 The effect of interstellar dust on starlight is
- Ato make stars appear less bright than expected by absorbing light about equally at all wavelengths.
- Bto scatter the red light from stars preferentially, making them appear more blue than expected.
- Cto dim and redden distant stars by preferentially scattering their blue light.
- Dalmost nonexistent, because light does not interact with dust.
145A particular giant molecular cloud has a mass of 400,000 solar masses. What is the mass of hydrogen in this cloud?
- A100,000 solar masses
- B392,000 solar masses
- C300,000 solar masses
- D4000 solar masses
146A T Tauri star is at what stage of its stellar evolution?
- Aat the end of its life—decaying away and cooling
- Bprotostar—before main-sequence phase
- Ca well-established main-sequence star
- Djust before red giant phase—when variability begins
147Which of the following trigger mechanisms for the initiation of stellar formation in gas and dust clouds produces many high mass O and B stars but only a few low-mass stars?
- Ashock waves from a supernova explosion
- Bgravitational condensation of the cloud
- Ccompression caused by the passage of the cloud through a galactic spiral arm
- Dthe passage of the cloud through a black hole
148What is believed to be the maximum mass that a star can have?
- Aabout 200 solar masses
- Babout 5 solar masses
- CThere appears to be no physical limit.
- Dabout 1000 solar masses
149How does the temperature of an interstellar cloud affect its ability to form stars?
- AHigher temperatures inhibit star formation.
- BHigher temperatures help star formation.
- CStar formation is so complicated that it is not possible to say how one quantity, such as temperature, affects it.
- DStar formation is independent of the temperature of the cloud.
150The light from a distant cloud of gas and dust looks distinctly red to the naked eye. When a spectrum is taken it is found that many wavelengths which would normally be expected to be in the middle of the spectrum have been shifted into the long wavelength end of the spectrum. Thus the red color in this situation is due to
- Aany one of these three phenomena.
- Bthe Balmer spectrum of hydrogen.
- Cthe Doppler effect.
- Dinterstellar reddening.
151An H II region is a region of
- Aneutral, atomic hydrogen in interstellar space.
- Bmolecular hydrogen inside a giant molecular cloud.
- Cgas and dust formed by the explosion of a massive star.
- Dionized hydrogen around one or more O and B stars.
152Which of the following is not a required condition for gas and dust to begin to condense into a protostar?
- Ahigh temperature, to ensure that gas atoms and dust particles collide with sufficient energy to stick together
- Bhigher than average density, to ensure that gravitational attraction is enhanced
- Clow mutual rotation, to avoid spin-off of material from the forming star
- Dlow temperature, to maintain low gas pressure in the cloud
153The main factor which determines the rate at which a protostar evolves is its
- Ainitial mass, larger masses evolving faster.
- Binitial mass, smaller masses evolving faster.
- Cenvironment, protostars with binary companions evolving much faster.
- Dinitial composition.
154At what stage of its evolutionary life is the Sun?
- Apost–main-sequence—red giant (cool) phase
- Bmain-sequence—middle age
- Cjust before supernova stage (perhaps 5 years)—late evolutionary stage
- Dpre–main-sequence—variable star
155 Suppose the light leaving a star has equal intensities in the blue and the red. The starlight passes through a dust cloud on its journey to Earth. When you observe the light reaching Earth you will find
- Athe red part of the spectrum will be more intense than the blue.
- Bthe blue part of the spectrum will be more intense than the red.
- Cthe blue and red intensities will still be equal, and they will be undiminished from the intensities which left the star.
- Dthe blue and red intensities will still be the same, although they will both be diminished from the intensities which left the star.
156Hydrogen atoms can be ionized by light with a wavelength of 9.12 × 10^–8 meters or shorter. What approximate temperature would a star need in order to have the peak of its spectrum at this wavelength?
- A51 million K
- B44,000 K
- C32,000 K
- D4 × 10^15 K
157A cocoon nebula is
- Aa giant molecular cloud containing young pre-stellar objects.
- Ba bright knot of ionized gas in the bipolar outflow from a young star.
- Ca dark globule of dust and gas silhouetted against a bright H II region.
- Da cloud of dust hiding a young protostar from sight.
158The total time that the Sun will spend as a main-sequence star is
- Aabout 1 million years
- Babout 10 million years (1067 years)
- Cabout 10 billion years (10^10 years)
- Dat least 200 billion years (2 × 10^11 years)
159What is the mass of a typical giant molecular cloud?
- A10 to 200 solar masses
- B10 million to 2 billion solar masses.
- C100,000 to 2,000,000 solar masses
- D1,000 to 20,000 solar masses
160Certain stages of stellar evolution, such as birth of a protostar and post-main sequence red giant evolution, come about because of an imbalance between gravity and
- Ahigh-energy neutrino pressure.
- Bradiation intensity.
- Cinternal gas pressure.
- Dthe centrifugal force from rotation.
161For any star on the main sequence, the same star when it was a protostar was
- Ahotter but not necessarily larger
- Blarger and cooler.
- Clarger and hotter.
- Dcooler but not necessarily larger.
162A Herbig-Haro object is
- Aa dark nebula which obscures distant stars from our view.
- Ba young protostar emerging from its nebula.
- Cglowing interstellar gas, heated by a high-velocity jet of matter from an evolving star.
- Dthe gas cloud produced by a supernova explosion.
163In the Hertzsprung-Russell diagram, how does the position of a typical star change while it is at the main-sequence phase of its evolution?
- AMassive stars ( > 4 solar masses) move toward the upper left as their luminosity increases, whereas lower-mass stars move toward the lower right as their temperature decreases, along the main sequence.
- BStars move from upper left to lower right along the main sequence.
- CA star does not move on the H-R diagram while it is at this phase of its life.
- DStars move from upper right to lower left along the main sequence.
164Which range of electromagnetic radiation is useful for observing new-born protostars within their gas and dust nebulas?
- Avisible
- Binfrared
- Chighly penetrating X-rays
- Dradio
165A star's evolutionary track is
- Aits movement when plotted on a Hertzsprung-Russell diagram, as it evolves in luminosity and temperature.
- Bits motion through the dark, dense cloud from which it was formed, marked by a visible channel swept free of dust and gas.
- Cits movement when plotted on a map of the galaxy as it takes part in the overall galactic rotation.
- Dts motion through the dark, dense cloud from which it was formed, marked by a visible channel swept free of dust and gas
166How is gas distributed in interstellar space?
- Aconcentrated around existing stars because of the stars' gravitational pull
- Bin clumps concentrated in interstellar clouds
- Cuniformly distributed through space
- Dconcentrated in thin walls throughout the universe
167Which of the following would not be found in higher-than-average densities in an interstellar nebula?
- Aprotons
- Bneutrinos
- Cdust
- Delectrons
168When a dark nebula collapses to form a group of stars, what is this stellar group called?
- Aa globular cluster
- Ban open cluster
- Ca galaxy
- Da constellation
169We see an emission nebula predominantly in
- Ablue light, originally emitted by stars within the nebula but scattered by dust.
- Blight emitted by molecules in the dense clouds of gas surrounding the stars in the nebula.
- Clight emitted over a wide range of wavelengths by dust grains that have been heated by radiation from embedded stars.
- Dthe Balmer Ha red line, from recombination of electrons with nuclei in ionized hydrogen.
170The characteristics of an open cluster of stars are
- Amany thousands of stars, of very different ages, but the same chemical composition.
- Ba few hundred stars, often very young and still embedded in the gas and dust from which they were formed.
- Cmany thousands of stars, all very old, with very little evidence of elements heavier than helium, and no evidence of dust or gas in their vicinity.
- Dmany thousands of stars, mostly binary, of different ages.
171The light from a distant cloud of gas and dust looks distinctly red to the naked eye. When a spectrum is taken it is found that the red color comes from a single bright spectral line. Thus the red color in this situation is due to
- Athe Balmer spectrum of hydrogen.
- Binterstellar reddening.
- Cany one of these three phenomena.
- Dthe Doppler effect.
172The light from a distant cloud of gas and dust looks distinctly red to the naked eye. When a spectrum is taken it is found that the short wavelengths are all dimmed in their intensity compared to the longer wavelengths which are all more intense. Thus the red color in this situation is due to
- Aany one of these three phenomena.
- Bthe Doppler effect.
- Cinterstellar reddening.
- Dthe Balmer spectrum of hydrogen.
173The lowest mass that a protostar can have and still become a star (i.e., start thermonuclear reactions in its core) is
- Aslightly less than 1/100 of a solar mass.
- Bslightly less than 1/10 of a solar mass.
- Cabout half a solar mass.
- D8/10 of a solar mass.
174What is the similarity in physical principle between the mechanism at work in an emission nebula and that in a household fluorescent light bulb?
- ABoth depend on atomic ionization and subsequent recombination of atoms to produce light, mainly in specific spectral lines.
- BThe spectral lines they produce from hydrogen gas are the same in both the nebula and the fluorescent tube.
- CBoth depend on electrical energy to heat a gas; in a fluorescent bulb electric energy comes from the household supply, whereas in the emission nebula electrical energy arises from rapid motion of ionized gases.
- DBoth depend on heating of a neutral gas to produce a continuum spectrum.
175 If a protostar were able to contract (get smaller) without any change to its surface temperature, what would happen to its luminosity?
- AIt would decrease, due to the smaller surface area of the protostar.
- BIt would remain the same, because the temperature does not change.
- CIt would increase, due to the compression of the gas.
- DIt is not possible to predict the change in luminosity, because other factors are involved.
176Thermonuclear reactions convert hydrogen into helium in the core of a star during which phase of a star's life?
- Athe time when the star moves up the red giant branch for the first time
- Bthe main-sequence phase
- Cthe protostar phase
- Dthe horizontal branch phase
177What is the most abundant element in the universe?
- Ahydrogen
- Boxygen
- Chelium
- Dcarbon
178Typical gas temperatures in dark Bok globules, the birthplaces of stars, are
- Ajust above that of the cosmic background radiation, at 3.5 K.
- B10 K.
- Cjust below freezing, at –3° C or 270 K.
- D100 K.
179At approximately what temperature will nuclear reactions begin in the core of a pre–main-sequence star?
- A500,000 K
- B5 million K
- C1 million K
- D50 million K
180What is a typical size for a giant molecular cloud?
- Aanything up to a light year across
- B10 light-years across
- C100 light-years across
- D1000 light-years across
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- Quiz on Astronomy 180, created by Trinity Higgs on 07/12/2017.
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