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Final Exam - Homework Questions
Terms in this set (174)
Rank the different layers of the Sun's atmosphere based on the order in which a probe would encounter them when travelling from Earth to the Sun's surface, from first encountered to last.
Corona, Chromosphere, Photosphere
Rank the layers of the Sun's atmosphere based on their density, from highest to lowest.
Photosphere, chromosphere, corona
Rank the layers of the Sun's atmosphere based on their temperature, from highest to lowest.
Corona, chromosphere, photosphere
Rank the layers of the atmosphere based on the energy of the photons that are typically emitted there, from highest to lowest.
Corona, chromosphere, photosphere.
Which changes would cause the fusion rate in the Sun's core to increase?
An increase in core temperature, and a decrease in the core radius.
What must occur in a star's core to reach equilbrium after an initial change in fusion rate?
If the fusion rate initially increases, then the core expands.
If the fusion rate initially decreases, then the core contracts.
What would happen if the fusion rate in the core of the Sun were increased but the core could not expand?
The Sun's core would start to heat up, and the rate of fusion would increase even more.
Nuclear fusion of hydrogen into helium occurs in the ___.
Energy moves through the Sun's ___ by means of rising of hot gas and falling of cooler gas.
Nearly all the visible light we see from the Sun is emitted from the ___
Most of the Sun's ultraviolet light is emitted from the narrow layer called the ___ where temperature increases with altitude.
We can see the Sun's ___
most easily during total solar eclipses.
The ___ is the layer of the Sun between its core and convection zone.
When are sunspots most numerous on the sun?
What occurs about 11 years after a solar maximum, on average?
When are solar flares most common?
When are orbiting satellites most at risk?
When are auroras most likely in Earth's skies?
What occurs about 5 to 6 years after a solar maximum on average?
X-ray images of the Sun generally show the
Which of these layers of the Sun is coolest?
Which of these groups of particles has the greatest mass?
Four individual protons
Scientists estimate the central temperature of the Sun using
mathematical models of the Sun
At the center of the Sun, fusion converts hydrogen into
helium, energy, and neutrinos.
Solar energy leaves the core of the Sun in the form of
Sunspots appear darker than their surroundings because they
are cooler than their surroundings.
What causes the cycle of solar activity?
Changes in the organization of the Sun's magnetic field
Which of these things poses the greatest hazard to communications satellites?
Particles from the sun
Which of the following years had the least sunspot activity?
What is the approximate range in latitude over which sunspots appear
Sunspots appear over a range of 40-50 degrees N latitude to 40-50 degrees S latitude
According to the figure, how do the positions of sunspots appear to change during one sunspot cycle? Do they get closer to or farther from the equator with time?
Sunspots get closer to the equator during a sunspot cycle.
Rank the stars based on their surface temperature from highest to lowest.
A blue white dwarf star, Sun, an orange main-sequence star, a red supergiant star
Where are red giant or supergiant stars found in the H-R diagram?
Upper right corner
What kind of stars are very cool, but very luminous?
Red giant or supergiant stars
What kind of stars are the majority of stars in our galaxy?
What kind of star is our Sun?
What kind of stars are the hottest and most luminous?
What kind of stars are very hot but very dim?
What kind of stars are not much larger in radius than Earth?
What properties of a star can we observe directly?
Apparent brightness, parallax angle, color, spectral type
What properties of a star can we infer directly?
Surface temperature, luminosity, mass, radius
What must we measure directly so that we can infer a star's surface temperature?
What must be true if we are to infer a star's luminosity directly from the inverse square law for light?
We have measured the star's apparent brightness
No interstellar gas or dust absorbs or scatters light between us and the star.
We have measured the star's distance.
We can measure a star's mass directly if
it is a member of an eclipsing binary system.
What must be true if the star's inferred mass is to be accurate?
We have determined that the star is a main-sequence star
We have measured that star's spectral type.
Before we can use parallax to measure the distance to a nearby star, we first need to know
The earth-sun distance
Which of the following is a valid way of demonstrating parallax for yourself?
Holding up your hand in front of your face.
What is the cause of stellar parallax?
Earth's orbit around the Sun.
The more distant a star, the
smaller its parallax angle
Approximately what is the parallax angle of a star that is 20 light-years away
Suppose that a star had a parallax angle of exactly 1 arcsecond. Approximately how far away would it be in light years?
Compared to a main-sequence star with a short lifetime, a main sequence star with a long lifetime is
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
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 smaller in radius
If the star Alpha Centauri were moved to a distance 10 times farther than it is now, its parallax angle would
What do we need to measure in order to determine a star's luminosity?
Apparent brightness and distance
What two pieces of information would you need in order to measure the masses of stars in an eclipsing binary system?
The time between eclipses and the average distance between the stars
Which of these stars has the coolest surface temperature?
Which of these stars is the most massive?
main-sequence A star
Which of these stars has the longest lifetime?
main-sequence M star
Which of these stars has the largest radius?
Supergiant M star
Which of these stars has the greatest surface temperature?
30Msun main-sequence star
Which of these star clusters is oldest
A cluster whose brightest main-sequence stars are yellow
What kind of stars end life as a supernova?
What kind of stars have higer fusion rate during main sequence life?
What kind of stars late in life fuse carbon into heavier elements?
What kind of star is our sun?
What kind of stars have longer lifetimes?
What kind of stars have their final corpse as a white dwarf
What kind of stars end life as a planetary nebula?
Rank the stages during the life of a high mass stars based on when they occur, from first to last.
Contracting cloud of gas and dust, protostar, main sequence o star, red supergiant, supernova, neutron star
Rank the elements that can be produced during fusion in the core of a high mass main sequence star, from frist to last.
Helium, carbon, oxygen, iron.
Rank the stages during the life of a star with the same mass of the Sun based on when they occur, from first to last.
Contracting cloud of gas and dust, protostar, main-sequence G star, red giant, planetary nebula, white dwarf.
Stars can form most easily in clouds that are
cold and dense
Which of these stars does not have fusion occuring in its core?
A red giant
What will the Sun's approximate luminosity be during the subgiant stage?
When the Sun is a red giant, what will its approximate surface temperature be?
Just before the Sun produces a planetary nebula, what will its approximate luminosity be?
When the Sun becomes a white dwarf with a surface temperature similar to its current surface temperature, what will its luminosity be?
From the viewpoint of an observer in the orbiting rocket, what happens to time on the other rocket as it falls toward the event horizon of the black hole.
Time runs increasingly slower as the rocket approaches the black hole.
As the falling rocket plunges toward the event horizon, an observer in the orbiting rocket would see that the falling rocket
slows down as it approaches the evnet horizon and never actually crosses the event horizon.
From Part B, you know that from afar you'll never see the infalling rocket cross the event horizon, yet it will still eventually disappear from view. Why?
Its light will become so redshifted that it will be undetectable.
If you were inside the rocket that falls toward the evnet horizon, you would notice your own clock to be running
at a constant, normal rate as you approach the event horizon.
If you were inside the rocket that falls toward the event horizon, from your own viewpoint you would
accelerate as you fall and cross the event horizon completely unhindered.
Which of these objects has the smallest radius?
1.2M sun white dwarf
Viewed from a distance, how would a flashing red light appear as it fell into a black hole?
Its flashes would shift to the infared part of the spectrum
Which of these black holes exerts the weakest tidal forces on an object near its event horizon?
10^6 M sun black hole.
What would happen if the Sun suddenly became a black hole without changing its mass?
Earth's orbit would not change.
Which of these binary systems is most likely to contain a black hole
An x-ray binary containing an o star and another object of equal mass.
What kind of stars all orbit in nearly the same plane?
What kind of stars are the youngest?
What kind of star is our sun?
What kind of stars are high-mass stars?
What kind of stars have orbits that can be inclined at any angle
What kind of stars are the oldest?
What kind of stars are found in globular clusters?
What kind of stars are stars with the smallest abundance of heavy elements
To calculate the dashed orbits from the stellar positions, astronomers had to assume that
if they observed for many more years, the dots would trace out ellipses.
Keeping in mind that all the stellar positions were measured at approximately one-year intervals, which stars are moving the fastest in their orbits during the time period indicated by the dots?
The dots farthest apart.
You've now found that the central object has a mass of about 4 million solar masses but is no more than about 70 AU in diameter—which means it cannot be much larger than the size of our planetary system. Why do these facts lead astronomers to conclude that the central object is a black hole?
There is no known way to pack so much mass into such a small volume without it collapsing into the black hole.
The circular but relatively flat portion of the galaxy is the
The first portion of the galaxy to form was the
A tightly packed group of a few hundred thousand very old stars is a
A ___ stands out in a photo of a galaxy because it shines brightly with light from massive young stars and glowing clouds of gas and dust
Our milky way galaxy is a ___
Stars orbiting in the ___ near the galaxy's center can have orbits highly inclined to the galactic plane.
Which part of the galaxy contains the coldest gas?
Why do disk stars bob up and down as they orbit the galaxy?
Because the gravity of other disk stars always pulls them toward the disk.
Which part of the galaxy has gas with the hottest average temperature?
What is the typical percentage (by mass) of elements other than hydrogen and helium in stars that are forming right now in the vicinity of the sun?
Where would you be most likely to find an ionization nebula?
In the disk
The best measurements of the mass of the black hole at the galactic center come from
the orbits of stars in the galactic center
Where are most of the Milky Way's globular clusters found?
In the halo
How do we determine the Milky Way's mass outside the Sun's orbit?
From the orbits of stars and gas clouds orbiting the galactic center at greater distances than the Sun
Where would you least expect to find an ionization nebula?
In the halo
Which kind of star is most likely to be a part of the spheroidal population?
An M star
What kind of galaxies contain abundant clouds of cool gas and dust?
What kind of galaxies have a flattened disk of stars?
What kind of stars have significant, ongoing star formation?
What kind of galaxies are rare in central regions of galaxy clusters?
What kind of galaxies contain many bright, hot stars?
What kind of galaxies are more reddish in color?
What kind of galaxies contain primarily old, low-mass stars
What type of galaxy is M82 based on its appearance in the visible light view?
What is the source of the white and blue light that dominates the image?
The infrared image of M82 shows a whitish-blue region running down the center, along with a much larger red region. What is emitting the light that is shown in red, and what is emitting the light that is shown in whitish-blue?
The red is emission from warm dust grains; the whitish blue is emission from stars
What statement provides the best interpretation of what we see in the multi image?
Stars in the central region of this galaxy are exploding as supernovae, generating a galactic wind of hot gas and warm dust grains.
What can we conclude about this galaxy from the fact that there are so many supernovae occuring?
This galaxy contains an unusually large number of young stars
Why do astronomers think that this is a burst of star fomration, rather than thinking that this galaxy always has such a high rate of star formation?
At its current rate of star formation, the galaxy would use up all its dust and gas in just a few hundred million years.
What baseline distance must we know before we can measure parallax?
The earth sun distance
Which cosmic distance measurement techniques are considered standard candle techniques?
Cepheids, main-sequence fitting, white dwarf supernovae
Suppose that Cepheids did not exist and there were no other standard candle technique that worked at the same distances. Which statement would be true?
We would not be able to measure the distances of distant galaxies.
Why do we use Hubble's law to estimate the distances of most distant galaxies, rather than using white dwarf supernovae in all cases?
We have not observed white dwarf supernovae in most galaxies.
Imagine that radar had never been invented and that we instead had to rely on a less reliable method of measuring distances in our solar system. If that method led us to underestimate the Earth-Sun distance by 10%, how would it affect other measurements in the distance chain?
They would be all off by the same 10 percent
Which technique is the most useful for measuring the distance to a galaxy located 10 million light-years away
Hubble's law expresses a relationship between
The distance of a galaxy and the speed at which it is moving away from us.
We can always determine the recession velocity of a galaxy from its redshift. But before we can use hubble's law, we must first calibrate it by
measuring the distances to many distant galaxies with a standard candle technique.
Suppose that you measure a galaxy redshift, and from the redshift you determine that its recession velocity is 30,000 kilometers per second. According to Hubble's law, approximate how far away is the galaxy
1.4 billion light-years
Based on what you have learned, which of the following best describes the meaning of Hubble's constant (H0)
It describes the expansion rate of the universe, with higher values meaning more rapid expansion
Which of these galaxies woudl you most likely find at the center of a large cluster of galaxies
a large elliptical galaxy
We can determine the distance of a cepheid by
determining its luminosity from the period-luminosity relation and then applying the inverse square law for light
We determine the distance of a cepheid by
determining its luminosity form the period-luminosity relation and then applying the inverse square law for light
Which kind of object is the best standard candle for measuring distances to extremely distant galaxies
a white dwarf supernova
Why do virtually all the galaxies in the universe appear to be moving away from our own?
Because expansion causes all galaxies to move away from nearly all others
Which of these galaxies is most likely to be oldest
A galaxy in the local grouip
When we observe a distant galaxy whose photons have traveled for 10 billion years before reaching Earth, we see that galaxy as it was when the universe was
4 billion years old
What happened within the first five minutes of the big bang?
Antielectrons (positrons) as common as electrons
Temperature fell to 10^15K
Strong force and electroweak force first became distinct
What happened after the first five minutes after the big bang?
Galaxies formed, stars formed, carbon nuclei formed, photons of cosmic microwave background released.
Rank the eras in the history of the universe from first to last
The charge of an antiproton is
When a proton and antiproton collide, they
convert into two photons
The current temperature of the universe as a whole is
a few K
When the universe was 380,000 years old, its thermal radiation spectrum consisted mostly of
visible and infared photons
Which of the following does not provide strong evidence for the Big Bang theory
Observations of the amount of hydrogen in the universe.
Which of the following does inflation help to explain?
The uniformity of the cosmic microwave background
Origin of galaxies
Which of these pieces of evidence supports the idea that inflation really happened?
Observations of the cosmic microwave background that indicate a flat geometry for the universe?
What is the earliest time in the universe that we can directly observe?
A few hundred thousand years after the big bang
Which of the following best explains why the night sky is dark
The observable universe is not infinite
A massive object can distort the light of more distant objects behind it through the phenomenon that we call
___ are defined as subatomic particles that have more mass than neutrinos but do not interact with light
The ___ of spiral galaxies provide strong evidence for the existence of dark matter
Matter made from atoms, with nuclei consisting of protons and neutrons, represents what we call ___ matter
ordinary (or baryonic)
Models show that the ___ of the universe is better-explained when we include the effects of dark matter along with the effects of luminous matter
Matter consisting of particles that differ from those foudn in atoms is generally referred to as ___ matter
exotic (or nonbaryonic)
Rank each model for long term expansion of the universe from smallest ratio to largest
coasting universe, critical universe, recollapsing universe
Rank each model for long term expansion of the universe from smallest distance between galaxies five billion years from now
recollapsing universe, critical universe, coasting universe, accelerating universe
Rank each model for long term expansion of the universe from smallest ratio to largest based on their prediction for the current age of the universe, from youngest to oldest.
recollapsing universe, critical universe, coasting universe, accelerating universe.
Dark matter is inferred to exist because
we can observe its gravitational influence on visible matter
Dark energy has been hypothesized to exist in order to explain
observations suggesting that the expansion of the universe is expanding
Strong evidence for the existence of dark matter comes from observaetions of
cluster of galaxies
A photograph of a cluster of galaxies shows distorted images of galaxies that lie behind it at greater distances. This is an example of what astronomers call
a gravitational lens
Based on the observational evidence, it is possible that dark matter doesn't really exist?
Yes, but only if there is something wrong with our current understanding of how gravity should work on large scales
Based on the current evidence, which of the following is considered a likely candidate for the majority of the dark matter in galaxies?
subatomic particles that we have not yet detected?
The major evidence for the idea that the expansion of the universe is accelerating comes from observations of
white dwarf supernovae
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