WorksheetsAstronomy Stars
Total questions: 51
Worksheet time: 3hrs 33mins
When is/was gravitational contraction an important energy-generation mechanism for the Sun?
only during solar minimum
only during solar maximum
when the Sun was being formed from a collapsing cloud of gas
right after the Sun began fusing hydrogen in its core
What do we mean when we say that the Sun is in gravitational equilibrium?
The hydrogen gas in the Sun is balanced so that it never rises upward or falls downward.
The Sun maintains a steady temperature.
This is another way of stating that the Sun generates energy by nuclear fusion.
There is a balance within the Sun between the outward push of pressure and the inward pull of gravity.
What is the Sun made of?
70 percent hydrogen, 28 percent helium, 2 percent other elements
50 percent hydrogen, 25 percent helium, 25 percent other elements
70 percent helium, 28 percent hydrogen, 2 percent other elements
98 percent hydrogen, 2 percent helium and other elements
What is the average temperature of the surface of the Sun?
1,000 K
6,000 K
10,000 K
1 million K
From the center outward, which of the following lists the "layers" of the Sun in the correct order?
core, radiation zone, convection zone, corona, chromosphere, photosphere
core, corona, radiation zone, convection zone, photosphere, chromosphere
core, radiation zone, convection zone, photosphere, chromosphere, corona
core, convection zone, radiation zone, photosphere, chromosphere, corona
Which layer of the Sun do we normally see?
photosphere
corona
chromosphere
convection zone
Why do sunspots appear dark in pictures of the Sun?
They are too cold to emit any visible light.
They actually are fairly bright but appear dark against the even brighter background of the surrounding Sun.
They are holes in the solar surface through which we can see to deeper, darker layers of the Sun.
They emit light in other wavelengths that we can't see.
Suppose that, for some unknown reason, the core of the Sun suddenly became hotter. Which of the following best describes what would happen?
Higher temperature would cause the rate of nuclear fusion to rise, which would increase the internal pressure, causing the core to expand and turn the Sun into a giant star.
Higher temperature would cause the rate of fusion to fall, decreasing the internal pressure and causing the core to collapse until the rate of fusion returned to normal.
The higher temperature would not affect the fusion rate but would cause the core to expand and cool until the temperature returned to normal, with the core at a new, slightly larger size.
Higher temperature would cause the rate of nuclear fusion to rise, which would increase the internal pressure, causing the core to expand and cool until the fusion rate returned to normal.
The overall fusion reaction by which the Sun currently produces energy is
3 H ⇒ 1 Li + energy.
3 He ⇒ 1 C + energy.
4 H ⇒ 4 He + energy.
4 H ⇒ 1 He + energy
What observations characterize solar maximum?
The Sun becomes much brighter.
The Sun emits light of longer average wavelength.
The Sun rotates faster at the equator
We see many sunspots on the surface of the Sun.
Why are neutrinos so difficult to detect?
because there are so rare
because they have no mass
because they move at nearly the speed of light
because they rarely interact with matter
What happens to energy in the convection zone of the Sun?
Energy slowly leaks outward through the diffusion of photons that repeatedly bounce off ions and electrons.
Energy is produced in the convection zone by nuclear fusion.
Energy is transported outward by the rising of hot plasma and the sinking of cooler plasma.
Energy is consumed in the convection zone by the creation of electrons and positrons.
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
a million years ago.
a thousand years ago.
ten years ago.
one year ago.
Since all stars begin their lives with the same basic composition, what characteristic most determines how they will differ?
location where they are formed
time they are formed
luminosity they are formed with
mass they are formed with
A star's luminosity is the
apparent brightness of the star in our sky.
surface temperature of the star.
total amount of light that the star will radiate over its entire lifetime.
total amount of light that the star radiates each second.
The spectral sequence in order of decreasing temperature is
OFBAGKM
OBAGFKM
OBAFGKM
ABFGKMO
On the main sequence, stars obtain their energy
from gravitational contraction.
by converting hydrogen to helium.
by converting helium to carbon, nitrogen, and oxygen.
from nuclear fission.
Which of the following is true about low-mass stars compared to high-mass stars?
Low-mass stars are cooler and less luminous than high-mass stars.
Low-mass stars are hotter and more luminous than high-mass stars.
Low-mass stars are cooler but more luminous than high-mass stars.
Low-mass stars are hotter but less luminous than high-mass stars.
Cluster ages can be determined from
main sequence fitting.
main sequence turnoff.
pulsating variable stars.
spectroscopic binaries.
What is interstellar reddening?
Interstellar dust absorbs more red light than blue light, making stars appear redder than their true color.
Interstellar dust absorbs more red light than blue light, making stars appear bluer than their true color.
Interstellar dust absorbs more blue light than red light, making stars appear bluer than their true color.
Interstellar dust absorbs more blue light than red light, making stars appear redder than their true color.
If you wanted to observe stars behind a molecular cloud, in what wavelength of light would you most likely observe?
ultraviolet
infrared
visible
gamma-ray
What is the likely reason that we cannot find any examples of the first generation stars?
The first generation stars were all very massive and exploded as supernova.
The first generation stars are too faint to be visible now.
The first generation stars formed such a long time ago that the light from them has not yet had time to reach us.
The first generation stars formed with only H and He and therefore have no spectral features.
What happens to the rotation of a molecular cloud as it collapses to form a star?
The rotation rate remains the same and results in stellar rotation.
The rotation dissipates and any residual is left in small overall rotation of the star.
The rotation rate increases and results in fast rotation of the star.
The rotation rate increases and results in a disk of material around a protostar.
When does a protostar become a true star?
when the star is 1 million years old
when the central temperature reaches 1 million Kelvin
when nuclear fusion begins in the core
when the thermal energy becomes trapped in the center
What is the smallest mass a newborn star can have?
8 times the mass of Jupiter
80 times the mass of Jupiter
800 times the mass of Jupiter
about 1/80 the mass of our Sun
No stars have been found with masses greater than 300 times our Sun because
they would generate so much power that they would blow themselves apart.
they shine exclusively at X-ray wavelengths and become difficult to detect.
they are not bright enough to be seen nearby.
molecular clouds do not have enough material to form such massive stars.
What do astronomers mean when they say that we are all "star stuff"?
that the carbon, oxygen, and many elements essential to life were created by nucleosynthesis in stellar cores
that Earth formed at the same time as the Sun
that life would be impossible without energy from the Sun
that the Sun formed from the interstellar medium: the "stuff" between the stars
Which of the following statements about degeneracy pressure is not true?
Degeneracy pressure can halt gravitational contraction of a star even when no fusion is occurring in the core.
Degeneracy pressure keeps any protostar less than 0.08 solar mass from becoming a true, hydrogen-fusing star.
Degeneracy pressure supports white dwarfs against gravity.
Degeneracy pressure varies with the temperature of the star.
What happens when a star exhausts its core hydrogen supply?
Its core contracts, but its outer layers expand and the star becomes bigger and brighter.
It contracts, becoming smaller and dimmer.
It contracts, becoming hotter and brighter.
It expands, becoming bigger but dimmer.
What is a planetary nebula?
a disk of gas surrounding a protostar that may form into planets
what is left of the planets around a star after a low-mass star has ended its life
the expanding shell of gas that is no longer gravitationally held to the remnant of a low-mass star
the molecular cloud from which protostars form
Which of the following sequences correctly describes the stages of life for a low-mass star?
white dwarf, main-sequence, red giant, protostar
protostar, red giant, main-sequence, white dwarf
protostar, main-sequence, white dwarf, red giant
protostar, main-sequence, red giant, white dwarf
What happens when the gravity of a massive star is able to overcome neutron degeneracy pressure?
The core contracts and becomes a white dwarf.
The core contracts and becomes a black hole.
The core contracts and becomes a ball of neutrons.
The star explodes violently, leaving nothing behind.
What happens to the core of a star after a planetary nebula occurs?
It contracts from a protostar to a main-sequence star.
It breaks apart in a violent explosion.
It becomes a white dwarf.
It becomes a neutron star.
Which of the following sequences correctly describes the stages of life for a low-mass star?
red giant, protostar, main-sequence, white dwarf
protostar, main-sequence, red giant, white dwarf
white dwarf, main-sequence, red giant, protostar
protostar, main-sequence, white dwarf, red giant
Which element has the lowest mass per nuclear particle and therefore cannot release energy by either fusion or fission?
hydrogen
oxygen
Silicon
iron
After a supernova event, what is left behind?
either a neutron star or a black hole
either a white dwarf or a neutron star
always a neutron star
always a black hole
Suppose a white dwarf is gaining mass because of accretion in a binary system. What happens if the mass someday reaches the 1.4-solar-mass limit?
The white dwarf undergoes a catastrophic collapse, leading to a type of supernova that is somewhat different from that which occurs in a massive star but is comparable in energy.
The white dwarf, which is made mostly of carbon, suddenly becomes much hotter in temperature and therefore is able to begin fusing the carbon. This turns the white dwarf back into a star supported against gravity by ordinary pressure.
The white dwarf immediately collapses into a black hole, disappearing from view.
A white dwarf can never gain enough mass to reach the limit because a strong stellar wind prevents the material from reaching it in the first place.
How does a 1.2-solar-mass white dwarf compare to a 1.0-solar-mass white dwarf?
It has a larger radius.
It has a smaller radius.
It has a higher surface temperature.
It has a lower surface temperature.
Observationally, how can we tell the difference between a white-dwarf supernova and a massive-star supernova?
A massive-star supernova is brighter than a white-dwarf supernova.
A massive-star supernova happens only once, while a white-dwarf supernova can repeat periodically.
The spectrum of a massive-star supernova shows prominent hydrogen lines, while the spectrum of a white-dwarf supernova does not.
The light of a white-dwarf supernova fades steadily, while the light of a massive-star supernova brightens for many weeks.
From an observational standpoint, what is a pulsar?
a star that slowly changes its brightness, getting dimmer and then brighter with a period of anywhere from a few hours to a few weeks
an object that emits flashes of light several times per second or more, with near perfect regularity
an object that emits random "pulses" of light that sometimes occur only a fraction of a second apart and other times stop for several days at a time
a star that changes color rapidly, from blue to red and back again
What is the basic definition of a black hole?
any compact mass that emits no light
a dead star that has faded from view
any object from which the escape velocity exceeds the speed of light
any object made from dark matter
How does a black hole form from a massive star?
During a supernova, if a star is massive enough for its gravity to overcome neutron degeneracy of the core, the core will be compressed until it becomes a black hole.
Any star that is more massive than 8 solar masses will undergo a supernova explosion and leave behind a black-hole remnant.
If enough mass is accreted by a white-dwarf star so that it exceeds the 1.4-solar-mass limit, it will undergo a supernova explosion and leave behind a black-hole remnant.
If enough mass is accreted by a neutron star, it will undergo a supernova explosion and leave behind a black-hole remnant.
What do we mean by the singularity of a black hole?
There are no binary black holes—each one is isolated.
It is the center of the black hole, a place of infinite density where the known laws of physics cannot describe the conditions.
It is the edge of the black hole, where one could leave the observable universe.
It is the "point of no return" of the black hole; anything closer than this point will not be able to escape the gravitational force of the black hole.
If you were to come back to our Solar System in 6 billion years, what might you expect to find?
a red giant star
a white dwarf
a rapidly spinning pulsar
a black hole
The following question refers to the sketch of the H-R diagram below. Please choose the best answer i.e., choice (a) refers to the entire main sequence, while (c) and (d) refer to only small parts of the main sequence. If choice (c) or (d) offers a better answer to a particular question than (a), use the best choice.
Which group includes stars that are fusing elements besides hydrogen in their cores?
a
b
c
d
e
The following question refers to the sketch of the H-R diagram below. Please choose the best answer i.e., choice (a) refers to the entire main sequence, while (c) and (d) refer to only small parts of the main sequence. If choice (c) or (d) offers a better answer to a particular question than (a), use the best choice.
Which group represents stars that are cool and dim?
a
b
c
d
e
The following question refers to the sketch of the H-R diagram below. Please choose the best answer i.e., choice (a) refers to the entire main sequence, while (c) and (d) refer to only small parts of the main sequence. If choice (c) or (d) offers a better answer to a particular question than (a), use the best choice.
Which group includes the Sun?
a
b
c
d
e
The following question refers to the sketch of the H-R diagram below. Please choose the best answer i.e., choice (a) refers to the entire main sequence, while (c) and (d) refer to only small parts of the main sequence. If choice (c) or (d) offers a better answer to a particular question than (a), use the best choice.
Which group represents hydrogen-fusing stars with the shortest lifetimes?
a
b
c
d
e
The following question refer to the representations below of H-R diagrams for different clusters of stars.
Which cluster is 10 billion years old?
a
b
c
d
The following question refer to the representations below of H-R diagrams for different clusters of stars.
Which cluster is the oldest?
a
b
c
d
The following question refer to the representations below of H-R diagrams for different clusters of stars.
Which cluster is the youngest?
a
b
c
d
