Astronomy 101 Exam 2 – Flashcards
Unlock all answers in this set
Unlock answersquestion
Which of the following forms of light can be observed with telescopes at sea level?
answer
visible light, radio waves
question
If our eyes were sensitive only to X rays, the world would appear __________.
answer
dark because X-ray light does not reach Earth's surface
question
If you had only one telescope and wanted to take both visible-light and ultraviolet pictures of stars, where should you locate your telescope?
answer
in space
question
Listed following are distinguishing characteristics and examples of reflecting and refracting telescopes. Match these to the appropriate category.
answer
Reflecting telescope: most commonly used by astronomers today, worlds largest telescope, the hubble space telescope
Refracting telescope: very large telescopes become top heavy, the worlds largest is 1-meter in diameter, incoming light passes through glass, Galileo's telescopes
question
Find the speed for a star in which this line appears at wavelength 120.4 nm
Find the direction for a star in which this line appears at wavelength 120.4 nm .
answer
2960 km/s
Towards us
question
Find the direction for a star in which this line appears at wavelength 121.3 nm
Find the direction for a star in which this line appears at wavelength 121.3 nm
answer
740 km/s
Toward us
question
The Hubble Space Telescope obtains higher-resolution images than most ground-based telescopes because it is:
answer
above earths atmosphere
question
Suppose you watch a leaf bobbing up and down as ripples pass it by in a pond. You notice that it does two full up and down bobs each second. Which statement is true of the ripples on the pond?
answer
They have a frequency of 2 hertz.
question
Which of the following best describes why we say that light is an electromagnetic wave?
answer
The passage of a light wave can cause electrically charged particles to move up and down.
question
Which of the following statements about X rays and radio waves is not true?
answer
X rays travel through space faster than radio waves.
question
Each of the following describes an "Atom 1" and an "Atom 2." In which case are the two atoms different isotopes of the same element?
answer
Atom 1: nucleus with 7 protons and 8 neutrons, surrounded by 7 electrons; Atom 2: nucleus with 7 protons and 7 neutrons, surrounded by 7 electrons
question
Which of the following statements is true of green grass?
answer
It absorbs red light and reflects green light.
question
Which of the following conditions lead you to see an absorption line spectrum from a cloud of gas in interstellar space?
answer
The cloud is cool and lies between you and a hot star.
question
Which of the following statements about thermal radiation is always true?
answer
A hot object emits more radiation per unit surface area than a cool object.
question
Betelgeuse is the bright red star representing the left shoulder of the constellation Orion. All the following statements about Betelgeuse are true. Which one can you infer from its red color
answer
Its surface is cooler than the surface of the Sun.
question
Laboratory measurements show hydrogen produces a spectral line at a wavelength of 486.1 nanometers (nm). A particular star's spectrum shows the same hydrogen line at a wavelength of 486.0 nm. What can we conclude?
answer
The star is moving toward us.
question
Suppose that Star X and Star Y both have redshifts, but Star X has a larger redshift than Star Y. What can you conclude?
answer
Star X is moving away from us faster than Star Y.
question
Studying a spectrum from a star can tell us a lot. All of the following statements are true except one. Which statement is not true?
answer
The total amount of light in the spectrum tells us the star's radius.
question
The angular separation of two stars is 0.1 arcseconds and you photograph them with a telescope that has an angular resolution of 1 arcsecond. What will you see?
answer
The photo will seem to show only one star rather than two.
question
How does the light-collecting area of an 8-meter telescope compare to that of a 2-meter telescope?
answer
The 8-meter telescope has 16 times the light-collecting area of the 2-meter telescope.
question
Which of the following is not an advantage of the Hubble Space Telescope over ground-based telescopes?
answer
It is closer to the stars.
question
The Chandra X-ray Observatory must operate in space because:
answer
X rays do not penetrate Earth's atmosphere.
question
Which of the following is always true about images captured with X-ray telescopes?
answer
They are always shown with colors that are not the true colors of the objects that were photographed.
question
Betelgeuse is the bright red star representing the left shoulder of the constellation Orion. All the following statements about Betelgeuse are true. Which one can you infer from its red color?
answer
Its surface is cooler than the surface of the Sun.
question
Which of the following statements about electrons is not true?
answer
Electrons orbit the nucleus rather like planets orbiting the Sun.
question
Consider an atom of gold in which the nucleus contains 79 protons and 118 neutrons. What is its atomic number and atomic mass number?
answer
The atomic number is 79, and the atomic mass number is 197
question
Without telescopes or other aid, we can look up and see the Moon in the night sky because it
answer
reflects visible light.
question
If you heat a gas so that collisions are continually bumping electrons to higher energy levels, when the electrons fall back to lower energy levels the gas produces
answer
an emission line spectrum.
question
A gas heated to millions of degrees would emit
answer
mostly X-rays.
question
If we observe one edge of a planet to be redshifted and the opposite edge to be blueshifted, what can we conclude about the planet?
answer
The planet is rotating.
question
Suppose you see two stars: a blue star and a red star. Which of the following can you conclude about the two stars? Assume that no Doppler shifts are involved. (Hint: Think about the laws of thermal radiation.)
answer
The blue star has a hotter surface temperature than the red star.
question
Which of the following is not a good reason to place observatories on remote mountain tops?
answer
to be able to observe at radio wavelengths
question
In order for an atom to absorb a photon (a particle of light),
answer
the photon must have enough energy to remove an electron from the atom.
OR
the photon must have energy matching the difference in energy between energy levels in the atom.
question
Which of the following changes would cause the fusion rate in the Sun's core to increase?
answer
An increase in the core temperature, A decrease in the core radius
question
Which of the following must occur for a star's core to reach equilibrium after an initial change in fusion rate?
answer
If the fusion rate initially increases, then the core expands, If the fusion rate initially decreases, then the core contracts.
question
What would happen if the fusion rate in the core of the Sun were increased but the core could not expand?
answer
The Sun's core would start to heat up and the rate of fusion would increase even more.
question
According to modern science, approximately how old is the Sun?
answer
4.5 billion years
question
The source of energy that keeps the Sun shining today is _________.
answer
nuclear fusion
question
What two physical processes balance each other to create the condition known as gravitational equilibrium in stars?
answer
gravitational force and outward pressure
question
Which of the following correctly describes how the process of gravitational contraction can make a star hot?
answer
When a star contracts in size, gravitational potential energy is converted to thermal energy.
question
Which of these layers of the Sun is coolest?
answer
photosphere
question
When the temperature of the Sun's core goes down, what happens next?
answer
Fusion reactions slow down; the core shrinks and heats.
question
Which of the following statements is an inference from a model (rather than an observation)?
answer
The Sun's core is gradually turning hydrogen into helium.
question
How do we know how old the Sun is?
answer
from ages of solar system meteorites, based on radioactive elements
question
A solar model is used to calculate the expected temperature and density at all depths within the Sun. These results are then used to calculate the expected fusion rate within the Sun. We have confidence that the model is correct because it agrees with the observed characteristics of the Sun. Which of the following observations can be used to check that we really do know the Sun's internal fusion rate?
answer
Measurements of the Sun's total energy output into space, Observations of neutrinos coming from the Sun
question
How does the number of neutrinos passing through your body at night compare with the number passing through your body during the day?
answer
about the same
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
Which 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
Which of the following best describes why the Sun emits most of its energy in the form of visible light?
answer
Like all objects, the Sun emits thermal radiation with a spectrum that depends on its temperature, and the Sun's surface temperature is just right for emitting mostly visible light.
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
Every second, the Sun converts about 600 million tons of hydrogen into 596 million tons of helium. The remaining 4 million tons of mass is __________.
answer
converted to an amount of energy equal to 4 million tons times the speed of light squared
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
If the Sun's core suddenly shrank a little bit, what would happen in the Sun?
answer
The core would heat up, fusion rates would increase, the core would re-expand.
question
Why does the Sun emit neutrinos?
answer
Fusion in the Sun's core creates neutrinos.
question
If the Sun suddenly stopped emitting neutrinos, what might we infer (after checking that our neutrino detectors were still operational)?
answer
Fusion reactions in the Sun have ceased within the past few minutes.
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
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
By looking for the splitting of spectral lines in the Sun's spectrum
question
Satellites in low-Earth orbits are more likely to crash to Earth when the sunspot cycle is near solar maximum because __________.
answer
Earth's upper atmosphere tends to expand during solar maximum, exerting drag on satellites in low orbits
question
Which of the following choices is not a way by which we can study the inside of the Sun?
answer
We can send a space probe into the Sun's photosphere.
question
A computer accessory salesman attempts to convince you to purchase a "solar neutrino" shield for your new computer. (It's even "on sale"!) Why do you turn down this excellent offer?
answer
Neutrinos rarely, if ever, interact with your computer.
question
The Sun will exhaust its nuclear fuel in about ______.
answer
5 billion years
question
the source of energy that keeps the Sun shining today is _________
answer
nuclear fusion
question
Energy balance in the Sun refers to a balance between _________.
answer
the rate at which fusion generates energy in the Sun's core and the rate at which the Sun's surface radiates energy into space
question
When we say that the Sun is a ball of plasma, we mean that _________.
answer
the Sun consists of gas in which many or most of the atoms are ionized (missing electrons)
question
What is the Sun made of (by mass)?
answer
70% hydrogen, 28% helium, 2% other elements
question
From center outward, which of the following lists the "layers" of the Sun in the correct order?
answer
Core, radiation zone, convection zone, photosphere, chromosphere, corona
question
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
The Sun's average surface (photosphere) temperature is about ______
answer
5,800 K
question
What is the solar wind?
answer
a stream of charged particles flowing outward from the surface of the Sun
question
The fundamental nuclear reaction occurring in the core of the Sun is _________.
answer
nuclear fusion of hydrogen into helium
question
The proton-proton chain is _________.
answer
the specific set of nuclear reactions through which the Sun fuses hydrogen into helium
question
The overall result of the proton-proton chain is:
answer
4 H becomes 1 He + energy
question
To estimate the central temperature of the Sun, scientists _________.
answer
use computer models to predict interior conditions
question
Why are neutrinos so difficult to detect?
answer
They have a tendency to pass through just about any material without any interactions.
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
a few hundred thousand 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
They 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
Coronal mass ejections and other activity associated with the sunspot cycle can disrupt radio communications and knock out sensitive electronic equipment.
question
If the sun's surface cooled, how would its appearance change?
answer
It would appear more red.
question
Why do sunspots appear dark?
answer
They are regions that are significantly cooler than the rest of the photosphere.
question
The light radiated from the Sun's surface reaches Earth in about 8 minutes. However, the energy of this light was released by fusion in the Sun's core about
answer
several hundred thousand years ago
question
What is the solution to the solar neutrino problem?
answer
The electron neutrinos created in the Sun's core change into another type of neutrino that we did not detect.
question
Approximately how many neutrinos pass through your body each second?
answer
about a thousand trillion
question
Imagine that you are trying to stop neutrinos with a lead shield. How thick would you need to make this shield to ensure that it can stop a neutrino?
answer
about one light year
question
What would happen to the core of the sun if its temperature rose slightly?
answer
The rate at which fusion occurs would increase, leading to an expansion of the core, which would in turn cause the temperature to drop back down.
question
What is the only force that can overcome the repulsion between two positively charged nuclei to bind them into an atomic nucleus?
answer
the strong force
question
Suppose you try to bring two protons close together. Because of the electromagnetic force, the two protons will
answer
repel one another.
question
How much mass does the Sun lose through nuclear fusion per second?
answer
4 million tons
question
At the center of the Sun, nuclear fusion converts hydrogen into
answer
helium, gamma rays, and neutrinos.
question
By what process do nuclear power plants on the Earth generate energy?
answer
nuclear fission
question
By what process does the Sun generate energy?
answer
nuclear fusion
question
Before we can use parallax to measure the distance to a nearby star, we first need to know __________.
answer
the Earth-Sun distance
question
Which of the following is a valid way of demonstrating parallax for yourself?
answer
Hold up your hand in front of your face, and alternately close your left and right eyes.
question
What is the cause of stellar parallax?
answer
Earth's orbit around the Sun.
question
The more distant a star, the __________.
answer
smaller its parallax angle
question
Approximately what is the parallax angle of a star that is 20 light-years away?
answer
0.16 arcsecond
question
Suppose that a star had a parallax angle of exactly 1 arcsecond. Approximately how far away would it be, in light-years?
answer
3.3 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
If the star Alpha Centauri were moved to a distance 10 times farther than it is now, its parallax angle would
answer
get smaller.
question
What do we need to measure in order to determine a star's luminosity?
answer
apparent brightness and distance
question
What two pieces of information would you need in order to measure the masses of stars in an eclipsing binary system?
answer
the time between eclipses and the average distance between the stars
question
Compared to a main-sequence star with a short lifetime, a main-sequence star with a long lifetime is __________.
answer
less luminous, cooler, smaller, and less massive
question
Compared to a high-luminosity main-sequence star, stars in the upper right of the H-R diagram are __________.
answer
cooler and larger in radius
question
Compared to a low-luminosity main-sequence star, stars in the lower left of the H-R diagram are __________.
answer
hotter and smaller in radius
question
Since all stars begin their lives with the same basic composition, what characteristic most determines how they will differ?
answer
mass they are formed with
question
If the distance between us and a star is doubled, with everything else remaining the same, its luminosity
answer
remains the same, but its apparent brightness is decreased by a factor of four.
question
Which of the following correctly states the relationship between the apparent brightness, luminosity, and distance of a star?
answer
apparent brightness = luminosity/(4pi * (distance)^2)
question
You measure the parallax angle for a star to be 0.5 arcseconds. The distance to this star is
answer
2 parsecs.
question
The spectral sequence sorts stars according to
answer
surface temperature.
question
Which of the following stars are brightest at ultraviolet wavelengths?
answer
O and B stars
question
How is the lifetime of a star related to its mass?
answer
More massive stars live much shorter lives than less massive stars
question
What is the common trait of all main sequence stars?
answer
They generate energy through hydrogen fusion in their core.
question
Which of these star clusters is oldest?
answer
a cluster whose brightest main-sequence stars are yellow
question
On a Hertzsprung-Russell diagram, where would you find stars that have the largest radii?
answer
upper right
question
Which of the following is the most numerous type of main-sequence star?
answer
an M star
question
Which of the following stellar properties has the greatest range in values?
answer
luminosity
question
A star of spectral type G lives approximately how long on the main sequence?
answer
10 billion years
question
Which of the following statements about globular clusters is true?
answer
Most stars in the cluster are yellow or reddish in color.
question
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?
answer
10 billion years
question
A brown dwarf is
answer
an object not quite massive enough to be a star
question
Stars can form most easily in clouds that are
answer
cold and dense
question
What can we learn about a star from a life track on an H-R diagram?
answer
the surface temperature and luminosity the star will have at each stage of its life
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
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
a set of steps by which four hydrogen nuclei fuse into one helium nucleus
question
In order to predict whether a star will eventually fuse oxygen into a heavier element, you mainly want to know what fact about the star?
answer
its mass
question
Why is iron significant to understanding how a supernova occurs?
answer
Iron cannot release energy either by fission or fusion.
question
After 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
Where does gold (the element) come from?
answer
it is produced during the supernova explosions of high-mass stars
question
What did Carl Sagan mean when he said that we are all "star stuff"?
answer
that the carbon, oxygen, and other elements essential to life were created by nucleosynthesis in stellar cores
question
Which two energy sources can help a star maintain its internal thermal pressure?
answer
nuclear fusion and gravitational contraction
question
What can trigger the gravitational collapse of an interstellar gas cloud?
answer
an increase in density and a decrease in temperature
question
What is the source of luminosity for protostars that have not yet become hot enough for fusion in their cores?
answer
energy released by infalling matter
question
No stars are expected with masses greater than 150 times our Sun because
answer
they would generate so much power that they would blow themselves apart.
question
What eventually halts the gravitational collapse of an interstellar gas cloud that forms an object that is not massive enough to become a star?
answer
the crowding of electrons in the core
question
When does a star become a main-sequence star?
answer
when the rate of hydrogen fusion in the star's core is high enough to sustain gravitational equilibrium
question
I observed a white dwarf supernova occurring at the location of an isolated white dwarf (not a member of a binary system).
answer
This statement does not make sense. White dwarf supernovae arise from mass transfer from a companion star and thus cannot occur outside binary systems.
question
Which of these objects has the smallest radius?
answer
a 1.2MSun white dwarf
question
If your spaceship flew within a few thousand kilometers above the event horizon, you and your ship would be rapidly sucked into it.
answer
This statement does not make sense. A circular orbit, even at a distance of a few thousand kilometers above the event horizon is perfectly stable. If you use the engines of the spaceship to put it on such orbit, the spaceship will not be sucked into the black hole
question
What would happen if the Sun suddenly became a black hole without changing its mass?
answer
Earth's orbit would not change.
question
Viewed from a distance, how would a flashing red light appear as it fell into a black hole?
answer
Its flashes would shift to the infrared part of the spectrum.
question
Where do gamma-ray bursts tend to come from?
answer
extremely distant galaxies
question
Sirius, the brightest star in the night sky, is actually a binary star system: Sirius A is main-sequence star and Sirius B is a white dwarf. Nearly all the visible light we see from Sirius comes from Sirius A. But when we photograph the system with X-ray light, as shown here, Sirius B is the brighter of the two stars. Why?
answer
As a white dwarf, Sirius B is much hotter than Sirius A and thus emits more X-rays.
question
Which of the following best describes why a white dwarf cannot have a mass greater than the 1.4-solar-mass limit?
answer
Electron degeneracy pressure depends on the speeds of electrons, which approach the speed of light as a white dwarf's mass approaches the 1.4-solar-mass limit.
question
The white dwarf that remains when our Sun dies will be mostly made of ________.
answer
carbon
question
Which statement concerning black hole masses and Schwarzschild radii is not true?
answer
In a binary system with a black hole, the Schwarzschild radius depends on the distance from the black hole to the companion star.
question
Suppose you drop a clock toward a black hole. As you look at the clock from a high orbit, what will you notice?
answer
Time on the clock will run slower as it approaches the black hole, and light from the clock will be increasingly redshifted.
question
A neutron star is ________.
answer
the remains of a star that died in a massive star supernova (if no black hole were created)
question
A typical neutron star is more massive than our Sun and about the size (radius) of ________.
answer
a small asteroid (10 km in diameter)
question
What is the basic definition of a black hole?
answer
an object with gravity so strong that not even light can escape
question
What do we mean by the event horizon of a black hole?
answer
It is the point beyond which neither light nor anything else can escape.
question
Imagine that our Sun were magically and suddenly replaced by a black hole of the same mass (1 solar mass). What would happen to Earth in its orbit?
answer
Nothing; Earth's orbit would remain the same.
question
What is the ultimate fate of an isolated white dwarf?
answer
It will cool down and become a cold black dwarf.
question
How does a black hole form from a massive star?
answer
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.
question
Rank the following 4 items in order of increasing density (low to high).
answer
main-sequence star, white dwarf, neutron star, black hole singularity
question
Which stars are more common?
answer
white dwarfs
question
A white dwarf supernova event is very important to calibrating Hubble's Law. Why? Choose the best answer for the question.
answer
It is a very luminous standard candle.
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(n) ________.
answer
low-mass star
question
Carbon fusion occur in high-mass stars but not in low-mass stars because ________.
answer
the cores of low-mass stars never get hot enough for carbon fusion
question
Which event marks the beginning of a supernova?
answer
the sudden collapse of an iron core into a compact ball of neutrons
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 is more common: a star blows up as a supernova, or a star forms a planetary nebula/white dwarf system?
answer
Planetary nebula formation is more common.
question
What is the fate of an isolated brown dwarf?
answer
It will remain a brown dwarf forever.
question
How many helium nuclei fuse together when making carbon?
answer
3
question
What happens to the core of a star after it ejects a planetary nebula?
answer
It becomes a white dwarf.
question
What star is the most likely to have made the atoms of gold in your jewelry or your electronics?
answer
a high-mass star
question
Which type of star spends the shortest time as a main sequence star?
answer
O star
