What are the appropriate units for the Sun's luminosity?
answer
watts
question
The Sun's surface, as we see it with our eyes, is called the
answer
photosphere
question
What is the solar wind?
answer
It is the name we give to the gas (or plasma) particles flowing outward from the surface of the Sun into the solar system.
question
The fundamental nuclear reaction occurring in the core of the Sun is:
answer
Nuclear fusion of hydrogen to helium.
question
What is the proton-proton chain?
answer
It is the specific set of nuclear reactions through which the Sun fuses hydrogen into helium.
question
Why are neutrinos so difficult to detect?
answer
hey have a tendency to pass through just about any material without any interactions.
question
To estimate the central temperature of the Sun, scientists ______.
answer
use computer models to predict interior conditions.
question
Which statement best describes the solar neutrino problem?
answer
Early experiments designed to detect solar neutrinos found them, but in fewer numbers than had been expected.
question
The light radiated from the Sun's surface reaches Earth in about 8 minutes, but the energy of that light was released by fusion in the solar core about ______.
answer
one million years ago.
question
What happens to energy in the Sun's convection zone?
answer
Energy is transported outward by the rising of hot plasma and sinking of cooler plasma.
question
What do sunspots, solar prominences, and solar flares all have in common?
answer
The are all strongly influenced by magnetic fields on the Sun.
question
Which of the following is NOT a characteristic of the 11-year sunspot cycle?
answer
The sunspot cycle is very steady, so that each 11-year cycle is nearly identical to every other 11-year cycle.
question
How is the sunspot cycle directly relevant to us here on Earth?
answer
Solar flares and other activity associated with the sunspot cycle can disrupt radio communications and knock out sensitive electronic equipment.
question
In the late 1800s, Kelvin and Helmholtz suggested that the Sun stayed hot due to gravitational contraction. What was the major drawback to this idea?
answer
It predicted that the Sun could shine for about 25 million years, but geologists had already found that Earth is much older than this.
question
When is/was gravitational contraction an important energy generation mechanism for the Sun?
answer
It was important when the Sun was forming from a shrinking interstellar cloud of gas.
question
What do we mean when we say that the Sun is in gravitational equilibrium?
answer
There is a balance within the Sun between the outward push of pressure and the inward pull of gravity.
question
ich of the following is the best answer to the question "Why does the Sun shine?"
answer
As the Sun was forming, gravitational contraction increased the Sun's temperature until the core become hot enough for nuclear fusion, which ever since has generated the heat that makes the Sun shine.
question
How does the Sun's mass compare to Earth's mass?
answer
The Sun's mass is about 300,000 times the mass of the Earth.
question
The Sun's average surface (photosphere) temperature is about ______.
answer
5,800 K.
question
Why do sunspots appear dark in pictures of the Sun?
answer
They actually are fairly bright, but appear dark against the even brighter background of the surrounding photosphere.
question
The Sun's surface seethes and churns with a bubbling pattern. Why?
answer
We are seeing hot gas rising and cool gas falling due to the convection that occurs beneath the surface.
question
Which of the following correctly compares the Sun's energy generation process to the energy generation process in human-built nuclear power plants?
answer
The Sun generates energy by fusing small nuclei into larger ones, while our power plants generate energy by the fission (splitting) of large nuclei.
question
Which of the following best explains why nuclear fusion requires bringing nuclei extremely close together?
answer
Nuclei normally repel because they are all positively charged, and can be made to stick only when brought close enough for the strong force to take hold.
question
The overall result of the proton-proton chain is:
answer
4 H ( 1 He + energy.
question
ery second, the Sun converts 600 million tons of hydrogen into 596 million tons of helium. The remaining 4 million tons ______.
answer
are converted to an amount of energy equal to 4 million tons times the speed of light squared.
question
Suppose that, for some unknown reason, the core of the Sun suddenly became hotter and the rate of nuclear fusion thereby increased. What would happen next?
answer
The core would expand, reducing the pressure and temperature, and the rate of fusion would decrease until it returned to its original level.
question
Which of the following best explains why the Sun's luminosity gradually rises over billions of years?
answer
Fusion steadily decreases the number of independent particles in the core (since 4 hydrogen nuclei become just 1 helium nucleus), which allows gravity to compress and heat the core. This core heating increases the rate of fusion and hence increases the Sun's luminosity.
question
Why does the Sun emit neutrinos?
answer
Fusion in the Sun's core creates neutrinos as a byproduct.
question
Which of the following best describes the current status of our understanding of the solar neutrino problem?
answer
Experimental evidence suggests that solar neutrinos can change from electron neutrinos to other types of neutrinos during their journey to Earth. If confirmed, the solar neutrino problem appears to be solved.
question
How can we best observe the Sun's chromosphere and corona?
answer
The chromosphere is best observed with ultraviolet telescopes and the corona is best observed with X-ray telescopes.
question
The intricate patterns visible in an X-ray image of the Sun generally show ______.
answer
extremely hot plasma flowing along magnetic field lines.
question
How can we measure the strength of magnetic fields on the Sun?
answer
Magnetic fields can cause some spectral lines to split, so we can measure the Sun's magnetic field strength by carefully studying lines in the Sun's spectrum.
question
Satellites in low-Earth orbits are more likely to crash to Earth during the solar maximum periods of the sunspot cycle because ______.
answer
Earth's upper atmosphere tends to expand during solar maximum, exerting drag on satellites in low orbits.
question
What is the approximate chemical composition (by mass) with which all stars are born?
answer
three quarters hydrogen, one quarter helium, no more than 2% heavier elements
question
The total amount of power (in watts, for example) that a star radiates into space is called its ______.
answer
luminosity.
question
Assuming that we can always measure the apparent brightness of a star, what does the luminosity-distance formula allow us to do?
answer
It allows us to calculate a star's luminosity if we know its distance, or calculate its distance if we know its luminosity.
question
If star A has an apparent magnitude of 3 and star B has an apparent magnitude of 5, which star is brighter in our sky?
answer
Star A
question
Ten parsecs is about ______.
answer
32.6 light-years.
question
If star A is closer to us than star B, then Star A's parallax angle is ______.
answer
larger than that of Star B.
question
From hottest to coolest, the order of the spectral types of stars is:
answer
OBAFGKM
question
Our Sun is a star of spectral type _______.
answer
G
question
Astronomers can measure a star's mass in only certain cases. Which case below might allow astronomers to measure a star's mass?
answer
The star is a member of a binary star system.
question
Which of the following terms is given to a pair of stars that we can determine are orbiting each other only by measuring their periodic Doppler shifts?
answer
spectroscopic binary
question
The axes on a Hertzsprung-Russell (H-R) diagram represent ______.
answer
luminosity and surface temperature
question
What can we infer, at least roughly, from a star's luminosity class?
answer
Its radius.
question
On an H--R diagram, stellar radii ______.
answer
increase diagonally from the lower left to the upper right.
question
On an H--R diagram, stellar masses ______.
answer
can be determined from a star's position in the diagram only for main sequence stars, and decrease from upper left to lower right.
question
How is the lifetime of a star related to its mass?
answer
More massive stars live considerably shorter lives than less massive stars.
question
Each choice below lists a spectral type and luminosity class for a star. Which one is a red supergiant?
answer
Spectral type M2, luminosity class I
question
What is the common trait of all main sequence stars?
answer
They generate energy through hydrogen fusion in their core.
question
Suppose our Sun were suddenly replaced by a supergiant star. Which of the following would be true?
answer
Earth would be inside the supergiant.
question
What is a white dwarf?
answer
It is the remains of a star, comprised mostly of carbon, that no longer produces energy by nuclear fusion.
question
What is a Cepheid?
answer
It is a type of variable star for which the period of variability can tell us its luminosity.
question
ich of the following statements comparing open and globular star clusters is NOT true?
answer
Open and globular clusters each typically contain a few hundred stars.
question
What do we mean by the main-sequence turnoff point of a star cluster, and what does it tell us?
answer
It is the spectral type of the hottest main sequence star in a star cluster, and it tells us the cluster's age.
question
All stars are born with the same basic composition, yet stars can look quite different from one another. Which two factors primarily determine the innate characteristics of a star?
answer
Its mass and its stage of life.
question
Based on the definition of apparent brightness, which units are appropriate for its measurement?
answer
watts per square meter
question
Suppose two stars are identical except that one is twice as far away from us as the other. Which statement is true
answer
Both stars have the same luminosity, but the apparent brightness of the closer star is four times as great as that of the more distant star.
question
Suppose that a star has a parallax angle of 1/20 arcsecond. If so, it is ______.
answer
20 parsecs away.
question
The star Vega has an absolute magnitude of about 4 and an apparent magnitude of about 0. Based on the definitions of absolute and apparent magnitude, we can conclude that ______.
answer
Vega is nearer than 10 parsecs from Earth.
question
Which of the following statements about spectral types of stars is NOT generally true?
answer
The spectral type of a star can be used to determine its distance.
question
Sirius is a spectral type A star whereas Rigel is a spectral type B star. What can we conclude?
answer
Rigel has a higher surface temperature than Sirius.
question
Astronomers generally can measure a star's mass if only it is a member of a binary star system. What characteristics of the stars must we know to measure the masses of the stars in a binary system?
answer
Their orbital period and average orbital distance.
question
Careful measurements reveal that a star maintains a steady apparent brightness at most times, except that at precise intervals of 73 hours the star becomes dimmer for about 2 hours. The most likely explanation is that:
answer
The star is a member of an eclipsing binary star system.
question
To answer this question, refer to the labels (a) through (e) on the following sketch of an H--R diagram. [Note that choice (a) refers to the entire main sequence, while (c) and (d) refer to only small parts of the main sequence. If choices (c) or (d) offer better answers to the question than (a), use the best choice.] Which group represents stars that are cool and dim?
answer
D
question
To answer this question, refer to the labels (a) through (e) on the following sketch of an H--R diagram. [Note that choice (a) refers to the entire main sequence, while (c) and (d) refer to only small parts of the main sequence. If choices (c) or (d) offer better answers to the question than (a), use the best choice.] Which group represents stars of the largest radii?
answer
E
question
To answer this question, refer to the labels (a) through (e) on the following sketch of an H--R diagram. [Note that choice (a) refers to the entire main sequence, while (c) and (d) refer to only small parts of the main sequence. If choices (c) or (d) offer better answers to the question than (a), use the best choice.] Which group represents the most common type of stars?
answer
D
question
To answer this question, refer to the labels (a) through (e) on the following sketch of an H--R diagram. [Note that choice (a) refers to the entire main sequence, while (c) and (d) refer to only small parts of the main sequence. If choices (c) or (d) offer better answers to the question than (a), use the best choice.] Which group represents stars that are extremely bright and emit most of their radiation as ultraviolet light?
answer
C
question
To answer this question, refer to the labels (a) through (e) on the following sketch of an H--R diagram. [Note that choice (a) refers to the entire main sequence, while (c) and (d) refer to only small parts of the main sequence. If choices (c) or (d) offer better answers to the question than (a), use the best choice.] Which group represents stars with the longest main-sequence lifetimes?
answer
D
question
To answer this question, refer to the labels (a) through (e) on the following sketch of an H--R diagram. [Note that choice (a) refers to the entire main sequence, while (c) and (d) refer to only small parts of the main sequence. If choices (c) or (d) offer better answers to the question than (a), use the best choice.] Which group represents stars fusing hydrogen in their cores?
answer
A
question
To answer this question, refer to the labels (a) through (e) on the following sketch of an H--R diagram. [Note that choice (a) refers to the entire main sequence, while (c) and (d) refer to only small parts of the main sequence. If choices (c) or (d) offer better answers to the question than (a), use the best choice.] Which group represents stars that have no nuclear fusion in their cores?
answer
B
question
You observe a star in the disk of the Milky Way, and you want to plot the star on an H-R diagram. You will need to determine all of the following, except:
answer
mass of the star
question
The approximate main-sequence lifetime of a star of spectral type O is ______.
answer
3 million years
question
For a Cepheid variable star, the longer the time between peaks of brightness, the ______.
answer
greater the luminosity of the star
question
How did astronomers discover the relationship between spectral type and mass for main sequence stars?
answer
Astronomers discovered the relationship by measuring the masses of main sequence stars in binary systems, and assume that the same relationship holds for single stars as well.
question
The choices below each describe the appearance of an H--R diagram for a different star cluster. Which cluster is the youngest?
answer
The diagram shows main-sequence stars of every spectral type except O, along with a few giants and supergiants.
question
The choices below each describe the appearance of an H--R diagram for a different star cluster. Which cluster is most likely to be located in the halo of our galaxy?
answer
The diagram shows main-sequence stars of spectral types G, K, and M, along with numerous giants and white dwarfs.
question
Gravity would cause main-sequence stars to collapse if it were not for the opposing ______.
answer
thermal pressure
question
In the context of understanding stellar lives, by "high-mass" stars we mean:
answer
stars with mass more than about 8 times the mass of our Sun.
question
The interstellar clouds called molecular clouds are:
answer
the cool clouds in which stars form
question
What is a protostar?
answer
A very young star (relative to its lifespan).
question
What can we learn about a star from a life track on an H-R diagram?
answer
What surface temperature and luminosity the star will have at each stage of its life.
question
The vast majority of stars in a newly formed star cluster are ______.
answer
less massive than the Sun.
question
When does a star become a main-sequence star?
answer
A star becomes a main-sequence star when the rate of hydrogen fusion within the star's core becomes high enough to balance the rate at which the star radiates energy into space.
question
Which of the following statements about brown dwarfs is NOT true?
answer
Brown dwarfs will eventually collapse to become white dwarfs.
question
Which of the following lists the stages of life for a low-mass star in the correct order?
answer
protostar, main-sequence star, red giant, planetary nebula, white dwarf
question
When a main-sequence star exhausts its core hydrogen fuel supply:
answer
the core shrinks while the rest of the star expands.
question
The main source of energy for a star as it grows in size to become a red giant is ______.
answer
hydrogen fusion in a shell surrounding the central core.
question
The overall helium fusion reaction is:
answer
three helium nuclei fuse to form one carbon nucleus.
question
What is a helium flash?
answer
The sudden onset of helium fusion in the core of a low-mass star.
question
Which of the following statements about horizontal branch stars is NOT true?
answer
Horizontal branch stars have inert (non-burning) carbon cores.
question
What is a planetary nebula?
answer
Gas ejected from a low-mass star in the final stage of its life.
question
The ultimate fate of our Sun is to____.
answer
become a white dwarf that will slowly cool with time.
question
What is the CNO cycle?
answer
The CNO cycle is series of nuclear reactions with the final result being the fusion of four hydrogen nuclei into one helium nucleus.
question
Why is iron significant to understanding how a supernova occurs?
answer
Iron cannot release energy either by fission or fusion, so a star with an iron core has no way to generate additional energy to counteract the crush of gravity.
question
ter a supernova explosion, the remains of the stellar core ______.
answer
may be either a neutron star or a black hole.
question
Why is Supernova 1987A particularly important to astronomers?
answer
It is the nearest supernova to have occurred at a time when we were capable of studying it carefully with telescopes.
question
Algol consist of a 3.7 Msun main-sequence star and a 0.8 Msun subgiant. Why does this seem surprising, at least at first?
answer
The two stars should be the same age, so we'd expect the subgiant to be more massive than the main-sequence star.
question
Which two processes can generate energy to help a star maintain its internal thermal pressure?
answer
nuclear fusion and gravitational contraction
question
Our Sun is considered to be a ______.
answer
low-mass star
question
Close binary star systems are thought to form when _____.
answer
a protostar is spinning so fast that it splits in two.
question
Angular momentum plays an important role in star formation. Which of the following characteristics of a protostellar system is probably NOT strongly affected by the star's angular momentum?
answer
The onset of core hydrogen fusion.
question
Generally speaking, how does the surface temperature and luminosity of a protostar compare to the surface temperature and luminosity of the main-sequence star it becomes?
answer
A main-sequence star is hotter and dimmer than it was as a protostar.
question
der a large molecular cloud that will give birth to a cluster of stars. Which of the following would you expect to be true?
answer
few massive stars will form, live, and die before the majority of the star's clusters even complete their protostar stage.
question
We do not know for certain whether the general trends we observe in stellar birth masses also apply to brown dwarfs. But if they do, then which of the following would be true?
answer
Brown dwarfs would outnumber all ordinary stars.
question
Where would a brown dwarf be located on an H-R diagram?
answer
It would be located below and to the right of the lowest part of the main sequence.
question
This diagram represents the life track of a 1 solar mass star. Refer to the life stages labeled with roman numerals. During which stage is the star's energy supplied by primarily by gravitational contraction?
answer
ii
question
This diagram represents the life track of a 1 solar mass star. Refer to the life stages labeled with roman numerals. During which stage does the star have an inert (non-burning) helium core?
answer
iv
question
This diagram represents the life track of a 1 solar mass star. Refer to the life stages labeled with roman numerals. Which stage lasts the longest?
answer
iii
question
This diagram represents the life track of a 1 solar mass star. Refer to the life stages labeled with roman numerals. During which stage does the star have an inert (non-burning) carbon core surrounded by shells of helium and hydrogen burning?
answer
viii
question
This diagram represents the life track of a 1 solar mass star. Refer to the life stages labeled with roman numerals. What will happen to the star after stage viii?
answer
Its outer layers will be ejected as a planetary nebula and its core will become a white dwarf.
question
What process distributes most of the carbon in the universe?
answer
Winds from low-mass red giant stars.
question
Why can the fusion of carbon occur in intermediate- and high-mass stars but not in low-mass stars?
answer
It is because the cores of low-mass stars never get hot enough for carbon fusion.
question
Observations show that elements with atomic mass numbers divisible by 4 (such as oxygen--16, neon--20, and magnesium--24) tend to be more abundant in the universe than elements with atomic mass numbers in between. Why do we think this is the case?
answer
At the end of a high-mass star's life, it produces new elements through a series of helium capture reactions.
question
Which of the following statements about various stages of core nuclear burning (hydrogen, helium, carbon, etc.) in a high-mass star is NOT true?
answer
Each successive stage lasts for approximately the same amount of time
question
Which event marks the beginning of a supernova?
answer
The sudden collapse of an iron core into a compact ball of neutrons.
question
Suppose that the star Betelgeuse (the upper left shoulder of Orion) were to supernova tomorrow (as seen here on Earth). What would it look like to the naked eye?
answer
Betelgeuse would remain a dot of light, but would suddenly become so bright that, for a few weeks, we'd be able to see this dot in the daytime.
question
A spinning neutron star has been observed at the center of a ______.
answer
supernova remnant.
question
You discover a binary star system in which one star is a 15 Msun main-sequence star and the other is a 10 Msun giant. How do we believe that a star system such as this might have come to exist?
answer
The giant must once have been the more massive star, but is now less massive because it transferred some of its mass to its companion.
Haven't found what you need?
Search for quizzes and test answers now
Quizzes.studymoose.com uses cookies. By continuing you agree to our cookie policy
