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Astronomy Final

Under what circumstances can differentiation occur on a planet?
The planet must have a molten interior.
The terrestrial planet cores contain mostly metal because
metals sank to the center during a time when interiors were molten throughout.
The core, mantle, and crust of a planet are defined by differences in their
Which internal energy source produces heat by converting gravitational potential energy into thermal energy?
accretion and differentiation.
The relatively few craters that we see within the lunar maria
were formed by impacts that occurred after those that formed most of the craters in the lunar highlands.
Which of the following does not have a major effect in shaping planetary surfaces?
Which of the following describes tectonics?
the disruption of a planet's surface by internal stresses.
Which of the following best describes convection?
It is the process in which warm material expands and rises while cool material contracts and falls.
What are the circumstances under which convection can occur in a substance?
when the substance is strongly heated from underneath
The three principal sources of the internal heat of terrestrial planets are
accretion, differentiation, and radioactivity
Why does Earth have the strongest magnetic field among the terrestrial worlds?
It is the only one that has both a partially molten metallic core and reasonably rapid rotation.
What are the conditions necessary for a terrestrial planet to have a strong magnetic field?
both a molten metallic core and reasonably fast rotation
When we see a region of a planet that is not as heavily cratered as other regions, we conclude that
the surface in the region is younger than the surface in more heavily cratered regions.
What type of stresses broke Earth's lithosphere into plates?
the circulation of convection cells in the mantle, which dragged against the lithosphere
Which two geological processes appear to have been most important in shaping the present surface
of Venus?
volcanoes and tectonics
Which of the following show evidence of ancient river beds?
What are greenhouse gases?
gases that absorb infrared light
Sunsets are red because
sunlight must pass through more atmosphere, and this scatters even more light at bluer wavelengths, transmitting mostly red light.
In what ways is Earth different from the other terrestrial planets?
1) Its lithosphere is broken into plates that move around.
2) It has oxygen in its atmosphere.
3) Most of its surface is covered with liquid water.
4) Life can be found almost everywhere.
Earth's atmosphere contains only small amounts of carbon dioxide because
carbon dioxide dissolves in water, and most of it is now contained in the oceans and carbonate rocks
How do astronomers think Jupiter generates its internal heat?
by contracting, changing gravitational potential energy into thermal energy
How do the size and mass of Jupiter's core compare to the size and mass of Earth?
It is about the same size but is 10 times more massive
Why is Jupiter denser than Saturn?
The extra mass of Jupiter compresses its interior to a greater extent than that of Saturn.
Why is Neptune denser than Saturn?
It has a different composition than Saturn, including a higher proportion of hydrogen compounds and rocks.
Why is Saturn almost as big as Jupiter, despite its smaller mass?
Jupiter's greater mass compresses it more and increasing its density
How do the jovian planet interiors differ?
All have cores of about the same mass, but differ in the amount of surrounding hydrogen and helium.
Why do the jovian planet interiors differ?
Accretion took longer further from the Sun, so the more distant planets formed their cores later and
captured less gas from the solar nebula than the closer jovian planets.
Why does Jupiter have several distinct cloud layers?
Different layers represent clouds made of gases that condense at different temperatures.
Why are there no impact craters on the surface of Io?
Io did have impact craters but they have all been buried in lava flows
Which of the following is not due to tidal forces?
the retrograde orbit of Triton (a moon of Neptune)
Planetary rings are
1) nearer to their planet than any of the planet's large moons.
2) orbiting in the equatorial plane of their planet.
3) composed of a large number of individual particles that orbit their planet in accord with Kepler's
third law.
4) known to exist for all of the jovian planets.
Which of the following best describes the internal layering of Jupiter, from the center outward?
Core of rock, metal, and hydrogen compounds; thick layer of metallic hydrogen; layer of liquid hydrogen; layer of gaseous hydrogen; cloud layer
What is the Great Red Spot?
A long-lived, high-pressure storm on Jupiter
What atmospheric constituent is responsible for the blue color of Uranus and Neptune?
How does the strength of Jupiter's magnetic field compare to that of Earth's magnetic field?
Jupiter's magnetic field is about 20,000 times as strong as Earth's.
Which statement about planetary rings is not true?
Saturn's rings formed along with its moons 4.6 billion years ago
Which is closest to the temperature of the Sun's core?
10 million K
The core of the Sun is
much hotter and much denser than its surface.
Based on its surface temperature of 6,000 K, most photons that leave the Sun's surface lie in which
region of the electromagnetic spectrum?
Sunspots are cooler than the surrounding gas in the photosphere because
strong magnetic fields slow convection and prevent hot plasma from entering the region.
At the center of the Sun, nuclear fusion converts hydrogen into
helium, gamma rays, and neutrinos.
What is the only force that can overcome the repulsion between two positively charged nuclei to
bind them into an atomic nucleus?
The strong force
Studies of solar vibrations have revealed that
our mathematical models of the solar interior are fairly accurate.
When the temperature of the Sun's core goes down, what happens next?
Fusion reactions slow down, core shrinks and heats.
Which of the following quantities is equal to the energy per second generated by the Sun's nuclear
The luminosity of the Sun's photosphere
Order the interior layers of the Sun from the hottest to the coldest.
Core, radiation zone, convection zone, photosphere
All but one of the following statements describe why scientists doubt the solar sunspot cycle affects
global climate. Identify which statement is irrelevant to the explanation.
Solar winds can affect satellite communications
Why isn't the Sun shrinking or expanding?
Because gas pressure balances gravity in the Sun
Which of the following statements about the Sun is an inference from a model, not an observation?
The convection zone is cooler than the radiation zone.
Which of the following correctly describes how the process of gravitational contraction can make
a star hot?
When a star contracts in size, gravitational potential energy is converted to thermal energy
The source of energy that keeps the Sun shining today is ________.
nuclear fusion
When we say that the Sun is a ball of plasma, we mean that ________.
the Sun consists of gas in which many or most of the atoms are ionized (missing electrons)
What is the Sun made of (by mass)?
70% hydrogen, 28% helium, 2% other elements
The proton-proton chain is ________.
the specific set of nuclear reactions through which the Sun fuses hydrogen into helium
Every second, the Sun converts about 600 million tons of hydrogen into 596 million tons of helium
converted to an amount of energy equal to 4 million tons times the speed of light squared
Why do sunspots appear dark in pictures of the Sun?
They actually are fairly bright, but appear dark against the even brighter background of the surrounding photosphere
A star's luminosity is the
total amount of energy that the star radiates each second.
If the distance between us and a star is doubled, with everything else remaining the same, its luminosity
remains the same, but its apparent brightness is decreased by a factor of four.
You measure the parallax angle for a star to be 0.1 arcseconds. The distance to this star is
10 parsecs
Which of the following statements about apparent and absolute magnitudes is true?
1) The magnitude system that we use now is based on a system used by the ancient Greeks over 2,000
years ago that classified stars by how bright they appeared.
2) A star with an apparent magnitude of 1 appears brighter than a star with an apparent magnitude of 2.
3) The absolute magnitude of a star is another measure of its luminosity.
4) A star's absolute magnitude is the apparent magnitude it would have if it were at a distance of 10 parsecs from Earth.
The spectral sequence, in order of decreasing temperature, is
Which of the following statements about spectral types of stars is true?
1) The spectral type of a star can be used to determine its surface temperature.
2) The spectral type of a star can be used to determine its color.
3) A star with spectral type A is cooler than a star with spectral type B.
4) A star with spectral type F2 is hotter than a star with spectral type F3
Which of the following stars are brightest at ultraviolet wavelengths?
O and B stars
Which of the following best describes the axes of a Hertzsprung-Russell (H-R) diagram?
surface temperature on the horizontal axis and luminosity on the vertical axis
On a Hertzsprung-Russell diagram, where would you find stars that are cool and dim?
lower right
On a Hertzsprung-Russell diagram, where would you find stars that are cool and luminous?
upper right
On a Hertzsprung-Russell diagram, where would you find stars that have the largest radii?
upper right
On a Hertzsprung-Russell diagram, where on the main sequence would you find stars that have the
greatest mass?
upper left
On a Hertzsprung-Russell diagram, where would you find red giant stars?
upper right
On a Hertzsprung-Russell diagram, where would you find white dwarfs?
lower left
On the main sequence, stars obtain their energy
by converting hydrogen to helium
Which of the following luminosity classes refers to stars on the main sequence?
Which of the following comparisons between low-mass stars and high-mass stars is true?
Low-mass stars are cooler and less luminous than high-mass stars
Which of the following statements about open clusters is true?
All stars in the cluster are approximately the same age
Which of the following statements about globular clusters is true?
Most stars in the cluster are yellow or reddish in color.
Which two energy sources can help a star maintain its internal thermal pressure?
nuclear fusion and gravitational contraction
What can we learn about a star from a life track on an H-R diagram?
what surface temperature and luminosity it will have at each stage of its life
When does a star become a main-sequence star?
when the rate of hydrogen fusion in the star's core is high enough to sustain gravitational equilibrium
What is the fate of an isolated brown dwarf?
It will remain a brown dwarf forever.
What percentage of a star's total lifetime is spent on the main sequence?
What happens when a star like the sun exhausts its core hydrogen supply?
Its core contracts, but its outer layers expand and the star becomes bigger and brighter.
Why does a star grow larger after it exhausts its core hydrogen?
Hydrogen fusion in a shell outside the core generates enough thermal pressure to push the upper layers outward.
What happens after the helium flash?
The core quickly heats up and expands
What is a planetary nebula?
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 becomes a white dwarf.
Which of the following sequences correctly describes the stages of life for a low-mass star?
protostar, main-sequence, red giant, white dwarf
Based on its main-sequence turnoff point, the age of this cluster is
about 1 billion years
Which statement about the cluster is not true?
It probably contains no young stars at all.
Consider the star to which the arrow points. How is it currently generating energy?
by core hydrogen fusion
Consider the star to which the arrow points. Which of the following statements about this star is not
It is larger in radius than the Sun.
Which element has the lowest mass per nuclear particle and therefore cannot release energy by
either fusion or fission?
What happens when the gravity of a massive star is able to overcome neutron degeneracy pressure?
The core contracts and becomes a black hole.
After a supernova event occurring in a high-mass star, what is left behind?
either a neutron star or a black hole
Identify the correct sequence of life events for a high mass star.
Main sequence, red supergiant, supernova, neutron star
What is the CNO cycle?
a type of hydrogen fusion that uses carbon, nitrogen, and oxygen atoms as catalysts
A white dwarf is
the exposed core of a dead star, supported by electron degeneracy pressure.
Why is there an upper limit to the mass of a white dwarf?
The more massive the white dwarf, the greater the degeneracy pressure and the faster the speeds of its electrons. Near 1.4 solar masses, the speeds of the electrons approach the speed of light, and no more mass can be supported.
Suppose a white dwarf is gaining mass because of accretion from a binary companion. What
happens if its mass reaches the 1.4 solar mass limit?
The white dwarf (which is made mostly of carbon) suddenly detonates carbon fusion and this creates a white dwarf supernova explosion.
What is the upper limit to the mass of a white dwarf?
1.4 solar masses
Which of the following is closest in size (radius) to a white dwarf?
the Earth
Which of the following is closest in size (radius) to a neutron star?
a city
From an observational standpoint, what is a pulsar?
An object that emits flashes of light several times per second (or even faster), with near perfect regularity.
How do we know that pulsars must be neutron stars?
No massive object, other than a neutron star, could spin as fast as we observe pulsars to spin and remain intact.
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 pressure in the core, the core will collapse to a black hole
Which of the following statements about black holes is not true?
If the Sun magically disappeared and was replaced by a black hole of the same mass, the Earth
would soon be sucked into the black hole.
What is the origin of short gamma ray bursts?
It is not known but it may be the collision of a neutron star with a black hole.
If you were to come back to our Solar System in 6 billion years, what might you expect to find?
a white dwarf
Rank the following 4 items in order of increasing density (low to high)
Main sequence star, white dwarf, neutron star, black hole singularity
A white dwarf supernova leaves behind
According to our modern understanding, what is a nova?
An explosion on the surface of a white dwarf in a close binary system
What is the diameter of the disk of the Milky Way?
100,000 light years
What is the thickness of the disk of the Milky Way?
1,000 light years
What kinds of objects lie in the halo of our galaxy?
globular clusters
What kinds of objects lie in the disk of our galaxy?
A) open clusters
B) O and B stars
C) old K and M stars
D) gas and dust
What do we mean by the interstellar medium?
The gas and dust that lies in between the stars in the Milky Way galaxy
How can we see through the interstellar medium?
by observing at wavelengths (high-energy X-rays and long wavelength radio waves) that are not
absorbed by interstellar dust
Approximately how far is the Sun from the center of the galaxy?
28,000 light-years
How are interstellar bubbles made?
by the winds of massive stars and supernovae explosions
What produces the 21-cm radio line that we can be used to map the Milky Way Galaxy?
atomic hydrogen
Compared to our Sun, most stars in the halo are
old, red, and dim and have fewer heavy elements.
Compared with stars in the disk, orbits of stars in the halo
are elliptical, with random orientations
Approximately how long does it take the Sun to orbit the center of the Milky Way Galaxy?
230 million years
Where does most star formation occur in the Milky Way today?
in the spiral arms
What evidence supports the existence of a black hole at the center of our galaxy?
The motions of the gas and stars at the center indicate that it contains 4 million solar masses within a
region only 3 light-years across
Where does most star formation occur in the Milky Way today?
in the spiral arms
Suppose that we look at a photograph of many galaxies. Assuming that all galaxies formed at about
the same time, which galaxy in the picture is the youngest?
the one that is farthest away
Which of the following types of galaxies appear reddest in color?
Compared to spiral galaxies, elliptical galaxies are
redder and rounder
The disk component of a spiral galaxy includes which of the following parts?
spiral arms
What is the major difference between an elliptical galaxy and a spiral galaxy?
An elliptical galaxy lacks a disk component
Why are Cepheid variables important?
Cepheids variables are pulsating stars whose pulsation periods are directly related to their true
luminosities. Therefore they can be used as distance indicators.
What is a standard candle?
an object for which we are likely to know its true luminosity
Which of the following is true about irregular galaxies?
They were more common when the universe was younger.
How was Edwin Hubble able to use his discovery of Cepheids in Andromeda to prove that the
"spiral nebulae" were actually galaxies external to the Milky Way?
From the period-luminosity relation for Cepheids, he was able to determine the distance to
Andromeda. He showed that it was far outside the Milky Way Galaxy
What is Hubble's law?
The recession velocity of a galaxy is directly proportional to its distance
Which of the following is a consequence of Hubble's Law?
the more distant a galaxy is from us, the faster it moves away from us
What makes white-dwarf supernovae very good standard candles for distance measurements?
A) They are very bright, so they can be used to determine the distances to galaxies billions of lightyears away.
B) They should all have approximately the same luminosity
What is the most accurate way to determine the distance to a nearby star?
stellar parallax
What is the most accurate way to determine the distance to a distant galaxy?
Cepheid variables
How do observations of galaxies at different distances help us learn about galaxy evolution?
Observations of different distances show galaxies of different ages and therefore different stages of
Which of the following types of protogalactic clouds is most likely to form an elliptical galaxy?
a dense cloud with very little angular momentum
Why is a dense cloud more likely to produce an elliptical galaxy than a spiral galaxy?
The higher gas density forms stars more efficiently, so all the gas is converted into stars before a
disk can form.
What is a quasar?
the extremely bright center of a distant galaxy, thought to be powered by a supermassive black hole
Which of the following is evidence for supermassive black holes in active galaxies?
A) the discovery of powerful jets coming from a compact core
B) rapid changes in the luminosity of the galaxy nucleus
C) quasars emit approximately equal power at all wavelengths from infrared to gamma rays
D) the very high speeds of gas orbiting around the galactic nucleus
Most active galactic nuclei are at large distances from us; relatively few nearby galaxies harbor
active galactic nuclei. What does this imply?
Active galactic nuclei tend to become less active as they age
Which of the following is evidence for supermassive black holes in active galaxies?
A) the discovery of powerful jets coming from a compact core
B) rapid changes in the luminosity of the galaxy nucleus
C) quasars emit approximately equal power at all wavelengths from infrared to gamma rays
D) the very high speeds of gas orbiting around the galactic nucleus
Why do we call dark matter "dark"?
It emits no or very little radiation of any wavelength.
What evidence suggests that the Milky Way contains dark matter?
We observe clouds of atomic hydrogen far from the galactic center orbiting the galaxy at
unexpectedly high speeds, higher speeds than they would have if they felt only the gravitational
attraction from objects that we can see
What is the best alternative explanation for the dark matter in the Milky Way based on the observed
orbital motions of stars and gas?
There is something wrong with our understanding of how gravity works
The distribution of the dark matter in a spiral galaxy is
approximately spherical and about ten times the size of the galaxy halo.
When we measure the broadening of absorption lines in the spectrum of an elliptical galaxy, we can
how fast the stars in the galaxy are moving relative to one another.
Which of the following methods used to determine the mass of a cluster of galaxies does not depend
on Newton's law of gravity?
measuring the amount of distortion caused by a gravitational lens
A gravitational lens occurs when
a massive object bends light beams that are passing nearby.
Which of the following is not evidence for dark matter?
the expansion of the universe
Which of the following are candidates for galactic dark matter?
A) brown dwarfs
B) Jupiter-size objects
D) faint red stars
Why do we expect WIMPs to be distributed throughout galactic halos, rather than settled into the
galaxy's disk?
WIMPS cannot produce photons, and they rarely interact and exchange energy with other particles.
Which of the following best describes how galaxies are distributed on large scales in the universe?
Galaxies appear to be distributed in chains and sheets that surround great voids
What might be causing the universe to accelerate?
dark energy