How can we help?

You can also find more resources in our Help Center.

Mastering Astronomy Chapter 11

STUDY
PLAY
The overall result of the proton-proton chain is that __________.

individual protons are joined into long chains of protons
p + p becomes 2H + energy
6 H becomes 1 He + energy
4 H becomes 1 He + energy
4 H becomes 1 He + energy
Suppose you try to bring two protons close together. Because of the electromagnetic force, the two protons will

repel one another.
collide.
remain stationary.
attract one another.
join together to form a deuterium nucleus.
repel one another.
What is the only force that can overcome the repulsion between two positively charged nuclei to bind them into an atomic nucleus?

The gravitational force
The strong force
The electromagnetic force
The Coriolis force
The weak force
The strong force
What is the solution to the solar neutrino problem?

We did not know how to detect neutrinos.
The Sun is generating energy other than by nuclear fusion.
Not all fusion reactions create neutrinos.
The Sun is generating much less energy than we think it is.
The electron neutrinos created in the Sun's core change into another type of neutrino that we did not detect.
The electron neutrinos created in the Sun's core change into another type of neutrino that we did not detect.
When the temperature of the Sun's core goes down, what happens next?

Fusion reactions slow down, the core expands and heats.
Fusion reactions speed up, core expands and cools.
Fusion reactions speed up, the core shrinks and cools.
Fusion reactions slow down, core shrinks and heats.
Fusion reactions slow down, core shrinks and heats.
Which of the following statements is an inference from a model (rather than an observation)?

The corona is hotter than the photosphere.
The Sun emits neutrinos.
The photosphere is made out of mainly hydrogen and helium.
The photosphere emits visible light.
The Sun's core is gradually turning hydrogen into helium.
The Sun's core is gradually turning hydrogen into helium.
Although the Sun does not generate energy by gravitational contraction today, this energy-generation mechanism was important when the Sun was forming.

True
False
True
Nuclear power plants on Earth create energy in the same way as the Sun.

True
False
False
Study Labeling the H-R Diagram (Question 9) on Mastering Astronomy
The answer is not here!
Are these characteristics of red giant/super giant, main sequence stars, or white dwarfs?
Found in the upper right of the H-R diagram
Very cool but very luminous
Red giant/super giant
Are these characteristics of red giant/super giant, main sequence stars, or white dwarfs?
the sun, for example
the majority of most stars in our galaxy
a very hot and very luminous star
Main sequence
Are these characteristics of red giant/super giant, main sequence stars, or white dwarfs?
not much larger in radius than the earth
Very hot but very dim
White dwarf
Compared to a main-sequence star with a short lifetime, a main-sequence star with a long lifetime is __________.

more luminous, hotter, larger, and more massive
more luminous, hotter, smaller, and less massive
less luminous, cooler, larger, and more massive
less luminous, cooler, smaller, and less massive
less luminous, cooler, smaller, and less massive
Compared to a high-luminosity main-sequence star, stars in the upper right of the H-R diagram are __________.

hotter and larger in radius
cooler and larger in radius
cooler and smaller in radius
hotter and smaller in radius
cooler and larger in radius
Compared to a low-luminosity main-sequence star, stars in the lower left of the H-R diagram are __________.

hotter and larger in radius
cooler and larger in radius
cooler and smaller in radius
hotter and smaller in radius
hotter and smaller in radius
Are the following observed directly or inferred directly?
Apparent brightness
color
parallax angle
spectral type
Observed directly
Are the following observed directly or inferred directly?
Mass
Surface temperature
radius
luminosity
Inferred directly
From Part A, you know that surface temperature is a stellar property that we infer indirectly. What must we measure directly so that we can infer a star's surface temperature?

parallax angle
spectral type
mass
apparent brightness
Spectral type
Which of the following must be true if we are to infer (calculate) a star's luminosity directly from the inverse square law for light?
Check all that apply.

No interstellar gas or dust absorbs or scatters light between us and the star.
We have measured the star's apparent brightness.
We have measured the star's distance.
We have measured the star's spectral type.
The star must be a member of a binary system.
No interstellar gas or dust absorbs or scatters light between us and the star.
We have measured the star's apparent brightness.
We have measured the star's distance.
We found that mass must be inferred for the star described in Part A. However, we can measure a star's mass directly if __________.

it is near enough for us to measure its distance with parallax
we know its spectral type
it is a member of an eclipsing binary system
it is unusually high in mass
it is a member of an eclipsing binary system
You should now see that the reason the mass of the star in Part A must be inferred is that the star has no known orbiting objects, which means we cannot apply Newton's version of Kepler's third law. Which of the following must be true if the star's inferred mass is to be accurate?
Check all that apply.

We have determined that the star is a main-sequence star.
We have measured the star's spectral type.
We have measured the star's distance.
The star must be located within the Milky Way Galaxy and not in another galaxy.
We have determined that the star is a main-sequence star.
We have measured the star's spectral type.
f the star Alpha Centauri were moved to a distance 10 times farther than it is now, its parallax angle would

get larger.
get smaller.
stay the same.
get smaller
What do we need to measure in order to determine a star's luminosity?

apparent brightness and mass
apparent brightness and temperature
apparent brightness and distance
apparent brightness and distance
Don't forget to study the math on Mastering Astronomy
The answers are not here!
Before we can use parallax to measure the distance to a nearby star, we first need to know __________.

the distance to the nearest star besides the Sun
the month in which the star is observed
the Earth-Sun distance
the Sun's mass
The Earth-Sun distance
Which of the following is a valid way of demonstrating parallax for yourself?

Hold up your hand in front of your face, and move it slowly back and forth.
Hold up your hand in front of your face, and alternately close your left and right eyes.
Get a camera, and photogra ph a person who is running back and forth.
Look up at a star, and notice how it moves toward the western horizon during the night
Hold up your hand in front of your face, and alternately close your left and right eyes.
What is the cause of stellar parallax?
Stellar parallax is caused by
Earth's orbit around the Sun.
the gradual motion of stars in the local solar neighborhood.
the gradual change in the patterns of the constellations over thousands of years.
the varying speed of Earth in its orbit around the Sun.
Earth's orbit around the Sun.
The more distant a star, the __________.

slower its parallax occurs
faster its parallax occurs
smaller its parallax angle
larger its parallax angle
smaller its parallax angle
Approximately what is the parallax angle of a star that is 20 light-years away?

0.0072 arcsecond
0.16 arcsecond
4.5×10−5 arcsecond
0.33 arcsecond
0.16 arcsecond
Suppose that a star had a parallax angle of exactly 1 arcsecond. Approximately how far away would it be, in light-years?

8.7 light-years
1 light-year
2.1 light-years
3.3 light-years
3.3 light-years
Star A is identical to Star B, except that Star A is twice as far from us as Star B. Therefore:

Both stars have the same luminosity, but the apparent brightness of Star B is four times that of Star A.
Both stars have the same apparent brightness, but the luminosity of Star B is four times that of Star A.
Both stars have the same luminosity, but the apparent brightness of Star B is twice that of Star A.
Both stars have the same luminosity, but the apparent brightness of Star A is four times that of Star B.
Both stars have the same luminosity, but the apparent brightness of Star B is four times that of Star A.
A star with a parallax angle of 1/20 arcsecond is ________.

1/20 parsec away
20 parsecs away
10 parsecs away
20 light-years away
20 parsecs away
Sirius is a star with spectral type A star and Rigel is a star with spectral type B star. What can we conclude?

Sirius has a higher surface temperature than Rigel.
Sirius has a higher core temperature than Rigel.
Rigel has a higher core temperature than Sirius.
Rigel has a higher surface temperature than Sirius.
Rigel has a higher surface temperature than Sirius.
Study Concept questions 11.10 - 11.16 on Mastering Astronomy
The answers are not here!
What is the approximate chemical composition (by mass) with which all stars are born?

Three quarters hydrogen, one quarter helium, no more than 2% heavier elements
Half hydrogen and half helium
98% hydrogen, 2% helium
95% hydrogen, 4% helium, no more than 1% heavier elements
Three quarters hydrogen, one quarter helium, no more than 2% heavier elements
Our Sun is a star of spectral type ________.

M
F
G
S
G
How is the lifetime of a star related to its mass?

More massive stars live slightly shorter lives than less massive stars.
More massive stars live much shorter lives than less massive stars.
More massive stars live slightly longer lives than less massive stars.
More massive stars live much longer lives than less massive stars.
More massive stars live much shorter lives than less massive stars.
Suppose our Sun were suddenly replaced by a supergiant star. Which of the following would be true?

Earth would fly off into interstellar space.
The supergiant's surface temperature would be much hotter than the surface temperature of our Sun.
Earth would be inside the supergiant.
The supergiant would appear as large as the full Moon in our sky
Earth would be inside the supergiant
What is a white dwarf?

It is a star that follows a period-luminosity relation.
The remains of a star that ran out of fuel for nuclear fusion
A main sequence star of spectral type F, which tends to look white in color
It is a type of star that produces energy by gravitational contraction.
The remains of a star that ran out of fuel for nuclear fusion
Since all stars begin their lives with the same basic composition, what characteristic most determines how they will differ?

time they are formed
luminosity they are formed with
color they are formed with
mass they are formed with
location where they are formed
mass they are formed with
Which of the following stellar properties has the greatest range in values?

core temperature
mass
surface temperature
radius
luminosity
Luminosity
A star of spectral type G lives approximately how long on the main sequence?

10 million years
10,000 years
1,000 years
10 billion years
1 billion years
10 billion years
You observe a star cluster with a main-sequence turn-off point at spectral type G2 (the same spectral type as the Sun). What is the age of this star cluster?

4.6 billion years.
100 billion years.
10 billion years.
10,000 years.
You also need to know the luminosity class of the turn-off point to determine the age
10 billion years
Which of the following statements about open clusters is true?

All stars in the cluster are approximately the same age.
All stars in the cluster are approximately the same color.
All stars in the cluster will evolve similarly.
All stars in the cluster have approximately the same mass.
There is an approximately equal number of all types of stars in the cluster.
All stars in the cluster are approximately the same age.
An O-star has a hotter surface temperature than the Sun. Therefore, compared to the Sun,

its emission peaks in the infrared part of the spectrum.
it emits at about the same wavelengths as the Sun (similar peak) but it is much fainter.
it emits at about the same wavelengths as the Sun (similar peak) but it is much brighter.
its emission peaks in the blue part of the spectrum.
its emission peaks in the blue part of the spectrum.
What are the stages of life for a star with the same mass as the sun?
Contracting cloud of gas and dust
protostar
main sequence G star
red giant
planetary nebula
white dwarf
What is the sequence of stages of life for a star with the same mass as the sun?
Main sequence star
giant
super giant
white dwarf
Don't forget to study Process of Science: Evidence for How the Elements Were Created on Mastering Astronomy (41 of 61)
The answers are not here!
What are the stages of life of a high mass star?
Contracting cloud of gas and dust
protostar
Main sequence O star
Red supergiant
supernova
neutron star
What is the order of elements burned throughout the lifetime of a high mass star?
helium, carbon, oxygen, iron
Are the following part of the protostar phase or the main sequence phase?
Pressure and gravity or not precisely balanced
Radius much larger than the sun
Luminosity much larger than the sun
Energy generated by gravitational contraction
Protostar
Are the following part of the protostar phase or the main sequence phase?
Lasts about 10 billion years
Energy generated by nuclear fusion
Surface generates energy at the same rate that the core will radiate energy
Main sequence
How will an isolated, one solar-mass star die?

As a white dwarf
As a neutron star
As a white dwarf supernova
As a black hole
Uncertain, since stars can die in any number of ways.
As a white dwarf
What did Carl Sagan mean when he said that we are all "star stuff"?

that the Universe contains billions of stars
that life would be impossible without energy from the Sun
that the Sun formed from the interstellar medium: the "stuff" between the stars
that the Earth formed at the same time as the Sun
that the carbon, oxygen, and other elements essential to life were created by nucleosynthesis in stellar cores
that the carbon, oxygen, and other elements essential to life were created by nucleosynthesis in stellar cores
Which two energy sources can help a star maintain its internal thermal pressure?

nuclear fusion and chemical reactions
chemical reactions and gravitational contraction
nuclear fusion and nuclear fission
nuclear fission and gravitational contraction
nuclear fusion and gravitational contraction
nuclear fusion and gravitational contraction
What type of star is our Sun?

A high-mass star
An intermediate-mass star
A low-mass star
A low-mass star
No stars are expected with masses greater than 150 times our Sun because

they would be too massive for hydrogen fusion to occur in their cores.
they would generate so much power that they would blow themselves apart.
they would fragment into binary stars because of their rapid rotation.
molecular clouds do not have enough material to form such massive stars.
they would shine exclusively at X-ray wavelengths and would be difficult to detect.
they would generate so much power that they would blow themselves apart.
When does a star become a main-sequence star?

when a star becomes luminous enough to emit thermal radiation
when the rate of hydrogen fusion in the star's core is high enough to sustain gravitational equilibrium
when hydrogen fusion is occurring throughout the star's interior
the instant when hydrogen fusion first begins in the star's core
when the protostar assembles from its parent molecular cloud
when the rate of hydrogen fusion in the star's core is high enough to sustain gravitational equilibrium
Which of the following statements about degeneracy pressure is not true?

Degeneracy pressure is a consequence of the laws of quantum mechanics.
Degeneracy pressure varies with the temperature of the star.
Degeneracy pressure keeps any protostar less than 0.08 solar mass from becoming a true, hydrogen-fusing star.
Degeneracy pressure can halt gravitational contraction of a star even when no fusion is occurring in the core.
Degeneracy pressure varies with the temperature of the star.
What is the fate of an isolated brown dwarf?

It will remain a brown dwarf forever.
It will become a white dwarf.
It will slowly evaporate to nothing.
It will become a black hole.
It will become a neutron star.
It will remain a brown dwarf forever.
How many helium nuclei fuse together when making carbon?

2
4
3
It varies depending on the reaction.
Helium cannot fuse into carbon.
3
What is a planetary nebula?

a disk of gas surrounding a protostar that may form into planets
the expanding shell of gas that is no longer gravitationally bound to the remnant of a low-mass star
the expanding shell of gas that is left when a white dwarf explodes as a supernova
the molecular cloud from which protostars form
what is left of its planets after a low-mass star has ended its life
the expanding shell of gas that is no longer gravitationally bound to the remnant of a low-mass star
What happens to the core of a star after it ejects a planetary nebula?

It breaks apart in a violent explosion.
It becomes a neutron star.
It contracts from a protostar to a main-sequence star.
It becomes a white dwarf.
none of the above
It becomes a white dwarf.
What is the approximate range of masses that newborn main sequence stars can have?

0.1 to 1000 solar masses
0.1 to 10 solar masses
0.001 to 10 solar masses
0.1 to 150 solar masses
0.001 to 150 solar masses
0.1 to 150 solar masses
Which two processes can generate energy to help a star maintain its internal thermal pressure?

Nuclear fusion and nuclear fission
Nuclear fusion and gravitational contraction
Nuclear fusion and supernova
Nuclear fission and supernova
Nuclear fusion and gravitational contraction
Consider a large molecular cloud that will give birth to a cluster of stars. Which of the following would you expect to be true?

All the stars in the cluster will become main-sequence stars at about the same time.
All the stars in the cluster will be of about the same mass.
A few massive stars will form, live, and die before the majority of the star's clusters even complete their protostar stage.
All the stars in the cluster will have approximately the same luminosity and surface temperature.
A few massive stars will form, live, and die before the majority of the star's clusters even complete their protostar stage.
Where would a brown dwarf be located on an H-R diagram?

Above and to the left of the highest part of the main sequence
Below and to the right of the lowest part of the main sequence
In the upper right corner of the H-R diagram
In the lower left corner of the H-R diagram
Below and to the right of the lowest part of the main sequence
Carbon fusion occur in high-mass stars but not in low-mass stars because ________.

the cores of low-mass stars never get hot enough for carbon fusion
only high-mass stars do fusion by the CNO cycle
carbon fusion can occur only in the stars known as carbon stars
the cores of low-mass stars never contain significant amounts of carbon
the cores of low-mass stars never get hot enough for carbon fusion
Which event marks the beginning of a supernova?

The beginning of neon burning in an extremely massive star
The onset of helium burning after a helium flash
The sudden collapse of an iron core into a compact ball of neutrons
The sudden initiation of the CNO cycle
The sudden collapse of an iron core into a compact ball of neutrons
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?

We'd see a cloud of gas expanding away from the position where Betelgeuse used to be. Over a period of a few weeks, this cloud would fill our entire sky.
Because the supernova destroys the star, Betelgeuse would suddenly disappear from view.
Betelgeuse would suddenly appear to grow larger in size, soon reaching the size of the full Moon. It would also be about as bright as the full Moon.
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.
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.