Define the bold-faced vocabulary terms within the chapter.
Multiple Choice: 3, 18, 30, 38, 39, 40
Short Answer: 16
6.1 The Optical Telescope Revolutionized Astronomy
Characterize why telescopes are important astronomical tools.
Multiple Choice: 1, 2
Illustrate the processes of reflection and refraction.
Multiple Choice: 7, 8, 9, 12, 13, 14, 15, 16, 20
Short Answer: 4, 5, 11
Compare and contrast the design, construction, and optical characteristics of reflecting and refracting telescopes.
Multiple Choice: 4, 5, 6, 17, 19
Short Answer: 1, 2, 7, 8, 10
Relate resolution to telescope design.
Multiple Choice: 21, 22, 23
Short Answer: 9, 12, 13, 14
Illustrate the effects of atmospheric seeing.
Multiple Choice: 10, 11
Short Answer: 3, 6
Assess what makes a good location for a telescope on Earth.
6.2 Optical Detectors and Instruments Used with Telescopes
Relate the optical properties of the human eye to film or a CCD camera.
Multiple Choice: 24, 28, 35, 36
Short Answer: 15, 18
Explain why photographic plates and CCD cameras are important tools of astronomy.
Multiple Choice: 25, 26, 27, 33, 34, 42
Distinguish between imaging and spectroscopy.
Multiple Choice: 29, 31, 32
Short Answer: 17, 19, 20
6.3 Astronomers Observe in Wavelengths Beyond the Visible
Explain when and why it is advantageous or necessary to place telescopes in space.
Multiple Choice: 41, 45, 48
Compare and contrast the practical utility of observing on the ground and from space for different wavelengths.
Multiple Choice: 43, 44, 49
Short Answer: 21, 22, 23
Summarize the challenges and simplifications of observing in wavelengths other than optical.
Multiple Choice: 37, 46, 47, 50
Short Answer: 24
6.4 Planetary Spacecraft Explore the Solar System
Summarize reasons why spacecraft are needed to explore the solar system.
Multiple Choice: 52, 53, 55
Evaluate the cost and benefit of different kinds of spacecraft (flyby, orbiter, lander, probe).
Multiple Choice: 51, 54
Short Answer: 25, 26
6.5 Other Astronomical Tools Contribute to the Study of the Universe
Establish why other tools (particle accelerators and detectors, supercomputers) are important to astronomy.
Multiple Choice: 56, 57, 58, 59, 60, 61
Short Answer: 27, 28
Working It Out 6.1
Compute the magnification and light-collecting areas of different optical systems.
Multiple Choice: 62, 63
Short Answer: 29
Working It Out 6.2
Compute the diffraction limits of different optical systems.
Multiple Choice: 64, 65, 66, 67, 68, 69, 70
Short Answer: 30
MULTIPLE CHOICE
The telescope was invented by
Galileo Galilei, an Italian inventor.
Hans Lippershey, an eyeglass maker in the Netherlands.
Gote Reber, a German cabinetmaker.
Tycho Brahe, a Danish astronomer.
Johannes Kepler, a German mathematician.
ANS: B DIF: Easy REF: Section 6.1
MSC: Remembering
OBJ: Characterize why telescopes are important astronomical tools.
Which of the following was not discovered by Galileo using a telescope?
The Moon has a heavily cratered surface.
Jupiter has four moons that orbit around it.
Mars has a polar ice cap similar to Earth.
The planet Venus goes through phases similar to those of the Moon.
The Milky Way is a collection of countless numbers of individual stars.
ANS: C DIF: Easy REF: Section 6.1
MSC: Remembering
OBJ: Characterize why telescopes are important astronomical tools.
The aperture of a telescope is which of the following?
the length of the telescope
the diameter of the telescope tube
the diameter of the primary lens/mirror
the radius of the primary lens/mirror
the diameter of the secondary mirror
ANS: C DIF: Easy REF: Section 6.1
MSC: Remembering
OBJ: Define the bold-faced vocabulary terms within the chapter.
Why can a compound lens combat a refracting telescope’s chromatic aberration?
Red light is absorbed by a larger amount than blue light.
Red light is refracted by a larger amount than blue light, and different types of glass have different indexes of refraction.
Blue light is refracted by a larger amount than red light, and different types of glass have different indexes of refraction.
Blue light is absorbed by a larger amount than red light.
A compound lens cannot combat chromatic aberration.
ANS: C DIF: Medium REF: Section 6.1
MSC: Understanding
OBJ: Compare and contrast the design, construction, and optical characteristics of reflecting and refracting telescopes.
One reason to prefer a reflecting over a refracting telescope is
its lack of chromatic aberration.
its shorter length for the same aperture size.
its lack of an aperture limit.
its lighter weight for larger apertures.
all of the above
ANS: E DIF: Easy REF: Section 6.1
MSC: Remembering
OBJ: Compare and contrast the design, construction, and optical characteristics of reflecting and refracting telescopes.
Large reflecting telescopes have mirrors that are _________ in shape.
spherical
parabolic
convex
hyperbolic
cylindrical
ANS: B DIF: Easy REF: Section 6.1
MSC: Remembering
OBJ: Compare and contrast the design, construction, and optical characteristics of reflecting and refracting telescopes.
A beam of light passes from air to water at an incident angle of 40°, relative to a plane perpendicular to the boundary between the two. At what angle will it emerge into the water, relative to a plane perpendicular to the boundary?
less than 40°
exactly 40°
more than 40°
The beam of light does not emerge from the water.
There is not enough information to answer the question.
ANS: A DIF: Easy REF: Section 6.1
MSC: Applying
OBJ: Illustrate the processes of reflection and refraction.
Which of the following phenomena is shown in the figure below?
reflection
refraction
magnification
diffraction
interference
ANS: B DIF: Easy REF: Section 6.1
MSC: Applying
OBJ: Illustrate the processes of reflection and refraction.
Which of the following phenomena is shown in the figure below?
reflection
refraction
magnification
diffraction
interference
ANS: A DIF: Easy REF: Section 6.1
MSC: Applying
OBJ: Illustrate the processes of reflection and refraction.
The angular resolution of a ground-based telescope (without adaptive optics) is typically
30 arcseconds (arcsec).
1 arcminutes (arcmin).
10 arcsec.
1 arcsec.
30 arcmin.
ANS: D DIF: Easy REF: Section 6.1
MSC: Remembering
OBJ: Illustrate the effects of atmospheric seeing.
Cameras that use adaptive optics provide higher spatial resolution images primarily because
they operate above Earth’s atmosphere.
they capture infrared light, which has a longer wavelength than visible light.
deformable mirrors are used to correct the blurring due to Earth’s atmosphere.
composite lenses correct for chromatic aberration.
they simulate a much larger telescope.
ANS: C DIF: Medium REF: Section 6.1
MSC: Understanding
OBJ: Illustrate the effects of atmospheric seeing.
According to the law of reflection, if a beam of light strikes a flat mirror at an angle of 30° relative to a plane perpendicular to the surface of the mirror, at what angle will it reflect, relative to a plane perpendicular to the surface of the mirror?
0°
30°
60°
90°
120°
ANS: B DIF: Medium REF: Section 6.1
MSC: Applying
OBJ: Illustrate the processes of reflection and refraction.
A prism is able to spread white light out into a spectrum of colors based on the property of
reflection.
refraction.
magnification.
resolution.
aberration.
ANS: B DIF: Medium REF: Section 6.1
MSC: Understanding
OBJ: Illustrate the processes of reflection and refraction.
Which of the following phenomena is shown in the figure below?
reflection
chromatic aberration
diffraction
magnification
interference
ANS: B DIF: Medium REF: Section 6.1
MSC: Applying
OBJ: Illustrate the processes of reflection and refraction.
Chromatic aberration results from
blue light being reflected more than red light.
red light being reflected more than blue light.
red light being refracted more than blue light.
blue light being refracted more than red light.
a lens being polished incorrectly.
ANS: D DIF: Medium REF: Section 6.1
MSC: Understanding
OBJ: Illustrate the processes of reflection and refraction.
As a beam of light travels from one medium to another, the change in direction of the beam of light depends on
the wavelength of the light.
the index of refraction of the outgoing medium.
the index of refraction of the incoming medium.
the angle of incidence.
all of the above
ANS: E DIF: Medium REF: Section 6.1
MSC: Understanding
OBJ: Illustrate the processes of reflection and refraction.
Why do reflecting telescopes usually have a secondary mirror in addition to a primary mirror?
to increase the light-gathering power
to make the telescope shorter
to increase the magnification
to increase the focal length
to combat chromatic aberration
ANS: B DIF: Medium REF: Section 6.1
MSC: Understanding
OBJ: Compare and contrast the design, construction, and optical characteristics of reflecting and refracting telescopes.
The aperture of a telescope partially or totally determines its
focal length and magnification.
light-gathering power.
focal length.
light-gathering power and magnification.
light-gathering power and diffraction limit.
ANS: E DIF: Medium REF: Section 6.1
MSC: Remembering
OBJ: Define the bold-faced vocabulary terms within the chapter.
An object sits infinitely far away from a parabolic mirror. At what distance from the mirror will its image be created?
It will be imaged at half the focal length.
It will be imaged at the focal length.
It will be imaged at twice the focal length.
No image will be created (the beams would be reflected parallel to each other).
The image is created on the other side of the mirror.
ANS: B DIF: Difficult REF: Section 6.1
MSC: Applying
OBJ: Compare and contrast the design, construction, and optical characteristics of reflecting and refracting telescopes.
Which property of light is responsible for chromatic aberration?
reflection
interference
dispersion
diffraction
magnification
ANS: C DIF: Medium REF: Section 6.1
MSC: Remembering
OBJ: Illustrate the processes of reflection and refraction.
How does the resolution of a telescope depend on its focal length?
The longer the focal length, the better the resolution.
The longer the focal length, the worse the resolution.
There is no relation between resolution and focal length.
ANS: C DIF: Medium REF: Section 6.1
MSC: Applying
OBJ: Relate resolution to telescope design.
In practice, the smallest angular size that one can resolve with a 10-inch telescope is governed by the
blurring caused by Earth’s atmosphere.
diffraction limit of the telescope.
size of the primary mirror.
motion of the night sky.
magnification of the telescope.
ANS: A DIF: Difficult REF: Section 6.1
MSC: Remembering
OBJ: Relate resolution to telescope design.
The 305-meter (-m) Arecibo radio telescope in Puerto Rico has a resolution that is closest to that of
the Hubble Space Telescope (0.1 arcsec).
a human eye (1 arcmin).
the Chandra X-ray telescope (0.5 arcsec).
a 1-m optical telescope (1 arcsec).
one of the 10-m Keck telescopes (0.0133 arcsec)
ANS: B DIF: Difficult REF: Section 6.1
MSC: Remembering
OBJ: Relate resolution to telescope design.
What part(s) of the human eye is responsible for detecting light?
cornea
lens
pupil
rods and cones
iris
ANS: D DIF: Easy REF: Section 6.2
MSC: Remembering
OBJ: Relate the optical properties of the human eye to film or a CCD camera.
Before charge-coupled devices (CCDs) were invented, what was the device most commonly used for imaging with optical telescopes?
Polaroid cameras
photographic glass plates
35-mm film
high-speed film
video cameras
ANS: B DIF: Easy REF: Section 6.2
MSC: Remembering
OBJ: Explain why photographic plates and CCD cameras are important tools of astronomy.
The major advantage CCDs have over other imaging techniques is that
they have a higher quantum efficiency.
they have a linear response to light.
they yield output in digital format.
they operate at visible and near-infrared wavelengths.
all of the above
ANS: E DIF: Easy REF: Section 6.2
MSC: Applying
OBJ: Explain why photographic plates and CCD cameras are important tools of astronomy.
Why do astronomers use monochromatic CCDs instead of color CCDs like your cell phone does?
Color CCDs have a smaller angular resolution.
They don’t make color CCDs large enough.
Monochromatic CCDs last longer.
Monochromatic CCDs have smaller angular resolution.
ANS: A DIF: Easy REF: Section 6.2
MSC: Understanding
OBJ: Explain why photographic plates and CCD cameras are important tools of astronomy.
Why can you see fainter stars with an 8-inch telescope than you can see with your naked eye?
The telescope collects light over a larger area.
The telescope magnifies the field of view.
The telescope collects light over a wider range of wavelengths than your eye.
The telescope has a wider field of view.
The telescope has a longer integration time than your eyes.
ANS: A DIF: Easy REF: Section 6.2
MSC: Understanding
OBJ: Relate the optical properties of the human eye to film or a CCD camera.
A diffraction grating is
a filter for imaging.
typically made from glass with many closely spaced lines engraved in it.
a prism.
a grism.
a spectrograph.
ANS: B DIF: Easy REF: Section 6.2
MSC: Remembering
OBJ: Distinguish between imaging and spectroscopy.
A spectrograph is
a device used for imaging.
typically made from glass with many closely spaced lines engraved in it.
a device used to measure the intensity of light at each wavelength.
a radio telescope.
a visible-light telescope.
ANS: C DIF: Medium REF: Section 6.2
MSC: Remembering
OBJ: Define the bold-faced vocabulary terms within the chapter.
Most modern spectrographs use a _________ to disperse the light from an object.
spherical mirror
lens
glass prism
diffraction grating
parabolic mirror
ANS: D DIF: Medium REF: Section 6.2
MSC: Remembering
OBJ: Distinguish between imaging and spectroscopy.
What property of light allows a grating to disperse the light from an object into a spectrum?
interference
reflection
refraction
aberration
magnification
ANS: A DIF: Medium REF: Section 6.2
MSC: Understanding
OBJ: Distinguish between imaging and spectroscopy.
Photography provides an improvement over naked-eye observations because
it is possible to observe a larger field of view with photographic plates.
the quantum efficiency is higher for photographic plates.
the image resolution is much better for photographic plates.
it is possible to detect fainter objects with the use of photographic plates.
the integration time is much shorter with the use of photographic plates.
ANS: D DIF: Medium REF: Section 6.2
MSC: Understanding
OBJ: Explain why photographic plates and CCD cameras are important tools of astronomy.
You are observing the Andromeda Galaxy using both photographic plates and a CCD. If you double the exposure time for both detectors, you
double the amount of light collected on both the photographic plate and the CCD.
double the amount of light collected on the only.
double the amount of light collected on the photographic plate, but the CCD collects less.
double the amount of light collected on the photographic plate, but the CCD collects more.
collect less than twice the amount of light on both the photographic plate and the CCD.
ANS: A DIF: Medium REF: Section 6.2
MSC: Understanding
OBJ: Explain why photographic plates and CCD cameras are important tools of astronomy.
If we could increase the quantum efficiency of the human eye, it would
allow humans to see a larger range of wavelengths.
allow humans to see better at night or other low-light conditions.
increase the resolution of the human eye.
decrease the resolution of the human eye.
not make a difference in the sight of the human eye.
ANS: B DIF: Medium REF: Section 6.2
MSC: Understanding
OBJ: Relate the optical properties of the human eye to film or a CCD camera.
Typically, video is shot using 24 to 30 frames per second (one frame each 33 to 42 ms). If a filmmaker shot new experimental video at 100 frames per second (one frame each 10 ms), how would it look during playback to the human eye if played at 100 frames per second?
It would look like the video was being fast-forwarded.
It would look like the video was about the same as normal video.
It would look like the video was being played back in slow motion.
It would look like a slideshow, a series of pictures on the screen each for a perceptible amount of time.
It would look like the video was about the same speed as normal video, but blurry.
ANS: B DIF: Difficult REF: Section 6.2
MSC: Understanding
OBJ: Relate the optical properties of the human eye to film or a CCD camera.
Arrays of radio telescopes can produce much better resolution than single-dish telescopes because they work based on the principle of
reflection.
refraction.
dispersion.
diffraction.
interference.
ANS: E DIF: Easy REF: Section 6.3
MSC: Understanding
OBJ: Summarize the challenges and simplifications of observing in wavelengths other than optical.,
An atmospheric window is
a giant glass dome.
a region of the electromagnet spectrum that can reach the ground.
a region of the electromagnet spectrum that cannot reach the ground.
ultraviolet.
X-rays.
ANS: B DIF: Easy REF: Section 6.3
MSC: Remembering
OBJ: Define the bold-faced vocabulary terms within the chapter.
The Jansky is a unit used to measure the strength of which type of source?
X-ray
ultraviolet
visible
infrared
radio
ANS: E DIF: Easy REF: Section 6.3
MSC: Remembering
OBJ: Define the bold-faced vocabulary terms within the chapter.
An interferometer requires a minimum of how many telescopes?
1
2
3
4
10
ANS: B DIF: Easy REF: Section 6.3
MSC: Remembering
OBJ: Define the bold-faced vocabulary terms within the chapter.
Which of the following is the best location for an infrared telescope on the ground?
at sea level
300 ft above sea level
1000 ft above sea level
6000 ft above sea level
10,000 ft above sea level
ANS: E DIF: Easy REF: Section 6.3
MSC: Remembering
OBJ: Explain when and why it is advantageous or necessary to place telescopes in space.
The first astronomical detector was
the CCD.
photoelectric tubes.
the human eye.
photographic plates.
35-mm film.
ANS: C DIF: Easy REF: Section 6.2
MSC: Remembering
OBJ: Explain why photographic plates and CCD cameras are important tools of astronomy.
You hear a news story about an X-ray telescope being built on Earth. You know this can’t be possible because
X-rays do not travel very far through Earth’s atmosphere.
X-ray telescopes are impossible to build.
X-ray telescopes would receive too much interference from hospitals.
it would cost too much money.
ANS: A DIF: Easy REF: Section 6.3
MSC: Remembering
OBJ: Compare and contrast the practical utility of observing on the ground and from space for different wavelengths.
Astronomers can use ground-based telescopes to observe in the majority of which of the following parts of the electromagnetic spectrum?
visible and infrared
visible and ultraviolet
visible and radio
visible, ultraviolet, and infrared
visible, infrared, and radio
ANS: C DIF: Easy REF: Section 6.3
MSC: Remembering
OBJ: Compare and contrast the practical utility of observing on the ground and from space for different wavelengths.
Water vapor in Earth’s atmosphere primarily absorbs which type of photons?
radio
infrared
visible
ultraviolet
X-ray
ANS: B DIF: Easy REF: Section 6.3
MSC: Remembering
OBJ: Explain when and why it is advantageous or necessary to place telescopes in space.
NASA’s Kuiper Airborne Observatory and the Stratospheric Observatory for Infrared Astronomy (SOFIA) are two examples of telescopes placed in high-flying aircraft. Why would astronomers put telescopes in airplanes?
to get the telescopes closer to the stars
to get the telescopes away from the light-pollution of cities
to get the telescopes above the majority of the water vapor in Earth’s atmosphere
to be able to observe one object for more than 24 hours without stopping
to allow the telescopes to observe the full spectrum of light
ANS: C DIF: Medium REF: Section 6.3
MSC: Understanding
OBJ: Summarize the challenges and simplifications of observing in wavelengths other than optical.
Which of the following is the biggest disadvantage of putting a telescope in space?
Astronomers don’t have as much control in choosing what to observe.
Astronomers have to wait until the telescopes come back to Earth to get their images.
Space telescopes can only observe in certain parts of the electromagnetic spectrum.
Space telescopes don’t last long before they fall back to Earth.
Space telescopes are much more expensive than similar ground-based telescopes.
ANS: E DIF: Medium REF: Section 6.3
MSC: Understanding
OBJ: Summarize the challenges and simplifications of observing in wavelengths other than optical.
Which of the following is not a reason to put a telescope in space?
to observe at wavelengths blocked by Earth’s atmosphere
to avoid light-pollution on Earth
to avoid weather on Earth
to avoid atmospheric distortion
to get closer to the stars
ANS: E DIF: Medium REF: Section 6.3
MSC: Understanding
OBJ: Explain when and why it is advantageous or necessary to place telescopes in space.
Ultraviolet radiation with wavelengths shorter than about 200 nm are hard to observe primarily because
Earth’s atmosphere easily absorbs it.
no space-based telescopes operate at ultraviolet wavelengths.
only the lowest mass stars emit ultraviolet light.
very few objects emit at ultraviolet wavelengths.
Earth emits too much ultraviolet background light.
ANS: A DIF: Medium REF: Section 6.3
MSC: Remembering
OBJ: Compare and contrast the practical utility of observing on the ground and from space for different wavelengths.
The first astronomical radio source ever observed was
the Andromeda Galaxy.
the galactic center, in the constellation Sagittarius.
thunderstorms.
Earth.
Jupiter.
ANS: B DIF: Medium REF: Section 6.3
MSC: Remembering
OBJ: Summarize the challenges and simplifications of observing in wavelengths other than optical.
Samples of which celestial object(s) have been brought back to Earth to be studied in detail?
a comet
the solar wind
an asteroid
the Moon
all of the above
ANS: E DIF: Easy REF: Section 6.4
MSC: Remembering
OBJ: Evaluate the cost and benefit of different kinds of spacecraft (flyby, orbiter, lander, probe).
Remote sensing instruments have been used to
map surfaces hidden beneath thick atmospheres.
measure the composition of atmospheres.
identify geological features.
watch weather patterns develop.
all of the above
ANS: E DIF: Medium REF: Section 6.4
MSC: Remembering
OBJ: Summarize reasons why spacecraft are needed to explore the solar system.
The Voyager 1 spacecraft is currently 18 billion km from Earth and heading out of our Solar System. How long does it take radio messages from Voyager 1 to reach us?
1.7 days
17 hours
17 days
17 weeks
17 minutes
ANS: B DIF: Medium REF: Section 6.4
MSC: Applying
OBJ: Summarize reasons why spacecraft are needed to explore the solar system.
Landers, rovers, and/or atmospheric probes have visited which object(s) listed below in an effort to gain new information about our Solar System?
Jupiter
Titan, Saturn’s moon
Mars
Eros, an asteroid
all of the above
ANS: E DIF: Medium REF: Section 6.4
MSC: Remembering
OBJ: Evaluate the cost and benefit of different kinds of spacecraft (flyby, orbiter, lander, probe).
In 2008, the Cassini spacecraft made a flyby of Enceladus, one of the icy moons of Saturn. If the spacecraft’s high-resolution camera had an angular resolution of 3 arcsec and it flew at an altitude of 23 km above Enceladus’s surface, how large an object could be resolved on the surface?
3 m
30 cm
30 km
5 cm
50 m
ANS: B DIF: Difficult REF: Section 6.4
MSC: Applying
OBJ: Summarize reasons why spacecraft are needed to explore the solar system.
Particle accelerators that smash atoms or particles together at high speeds, such as the Large Hadron Collider (LHC), are important tools used for simulating conditions in
the early universe.
the solar wind.
red giants.
brown dwarf stars.
planetary nebula.
ANS: A DIF: Easy REF: Section 6.5
MSC: Understanding
OBJ: Establish why other tools (particle accelerators and detectors, supercomputers) are important to astronomy.
Which of the following cannot be directly detected using a telescope?
X-rays
visible light
infrared light
neutrinos
ultraviolet light
ANS: D DIF: Easy REF: Section 6.5
MSC: Remembering
OBJ: Establish why other tools (particle accelerators and detectors, supercomputers) are important to astronomy.
What type of waves have not yet been directly detected by astronomers?
sound waves
gravitational waves
X-ray waves
gamma-ray waves
pressure waves
ANS: B DIF: Easy REF: Section 6.5
MSC: Remembering
OBJ: Establish why other tools (particle accelerators and detectors, supercomputers) are important to astronomy.
Telescopes and satellites such as Cosmic Background Explorer (COBE), Wilkinson Microwave Anisotropy Probe (WMAP), and Planck are designed to detect microwave radiation emitted by
galaxies.
black holes.
planets.
the Big Bang.
stars.
ANS: D DIF: Easy REF: Section 6.5
MSC: Remembering
OBJ: Establish why other tools (particle accelerators and detectors, supercomputers) are important to astronomy.
High-speed computers have become one of an astronomer’s most important tools. Which of the following does not require the use of a high-speed computer?
analyzing images taken with very large CCDs
generating and testing theoretical models
moving a telescope from object to object
studying the evolution of astronomical objects or systems over time
correcting for atmospheric distortion
ANS: C DIF: Medium REF: Section 6.5
MSC: Understanding
OBJ: Establish why other tools (particle accelerators and detectors, supercomputers) are important to astronomy.
Neutrino detectors typically capture one out of every _________ neutrinos that pass through them.
10
106 (one million)
109 (one billion)
1012 (one trillion)
1022 (10 billion trillion)
ANS: E DIF: Difficult REF: Section 6.5
MSC: Remembering
OBJ: Establish why other tools (particle accelerators and detectors, supercomputers) are important to astronomy.
The magnification of a telescope depends on the focal length of the telescope and
the size of the aperture.
the type of telescope (refracting vs. reflecting).
the wavelengths being observed.
the focal length of the eyepiece.
the angular resolution of the telescope.
ANS: D DIF: Easy REF: Working It Out 6.1
MSC: Remembering
OBJ: Compute the magnification and light-collecting areas of different optical systems.
Which telescope would collect 100 times more light than a 1-m telescope?
100-m telescope
80-m telescope
50-m telescope
30-m telescope
10-m telescope
ANS: E DIF: Medium REF: Working It Out 6.1
MSC: Applying
OBJ: Compute the magnification and light-collecting areas of different optical systems.
When we determine the angular resolution of an interferometric array of radio telescopes using the formula θ ∝ λ/D, the variable D stands for the
diameter of the telescopes.
separation between the telescopes.
magnification of the telescopes.
number of telescopes.
focal length of the telescopes.
ANS: B DIF: Easy REF: Working It Out 6.2
MSC: Understanding
OBJ: Compute the diffraction limits of different optical systems.
Which of the following phenomena is shown in the figure below?
reflection
chromatic aberration
refraction
magnification
interference
ANS: C DIF: Medium REF: Working It Out 6.2
MSC: Understanding
OBJ: Compute the diffraction limits of different optical systems.
The diffraction limit of a 4-m telescope is _________ than that of a 2-m telescope.
two times larger
four times larger
four times smaller
two times smaller
It depends on the type of telescope.
ANS: D DIF: Medium REF: Working It Out 6.2
MSC: Applying
OBJ: Compute the diffraction limits of different optical systems.
Grote Reber conducted the first radio survey of the sky in the 1930s and 1940s with his 9-m-diameter radio telescope. Why did his telescope need to be so large?
He needed a large light-collecting area because radio sources are notoriously dim.
He needed better angular resolution to identify sources because radio waves are so long.
He needed a higher magnification to identify sources because radio sources are quite small.
He needed a longer focal length because radio sources are so far away.
He needed a shorter focal length because radio sources are so far away.
ANS: B DIF: Medium REF: Working It Out 6.2
MSC: Applying
OBJ: Compute the diffraction limits of different optical systems.
The Search for Extraterrestrial Intelligence (SETI) project’s Allen Telescope Array will have 350 radio dishes, each with an individual diameter of 6 m, spread out over a circle whose diameter is 1 km. What would this array’s spatial resolution be when it operates at 6,000 MHz?
10 arcsec
0.10 arcsec
1 arcsec
10 arcmin
1.0 arcmin
ANS: A DIF: Difficult REF: Working It Out 6.2
MSC: Applying
OBJ: Compute the diffraction limits of different optical systems.
The two Keck 10-m telescopes, separated by a distance of 85 m, can operate as an optical interferometer. What is its resolution when it observes in the infrared at a wavelength of 2 microns?
0.01 arcsec
0.005 arcsec
0.4 arcsec
0.06 arcsec
0.2 arcsec
ANS: B DIF: Difficult REF: Working It Out 6.2
MSC: Applying
OBJ: Compute the diffraction limits of different optical systems.
The angular resolution of the largest single-dish radio telescope in the United States, the 100-m Green Bank Telescope, is _________ when it operates at a wavelength of 20 cm.
41 arcmin
6.8 arcmin
4.1 arcmin
6.8 arcsec
4.1 arcsec
ANS: B DIF: Difficult REF: Working It Out 6.2
MSC: Applying
OBJ: Compute the diffraction limits of different optical systems.
SHORT ANSWER
Explain why the largest telescopes are not refracting telescopes.
ANS: The larger the refracting telescope, the heavier the lens. If the lens is too massive, it will sag under the force of gravity and the image will be distorted.
DIF: Easy REF: Section 6.1 MSC: Understanding
OBJ: Compare and contrast the design, construction, and optical characteristics of reflecting and refracting telescopes.
Why do reflecting telescopes use curved mirrors instead of flat mirrors?
ANS: The purpose of a telescope is to redirect parallel beams of light from a distant object to converge at a point. A flat mirror would simply redirect them all at the same angle; therefore, they would still travel parallel to each other. A curved mirror reflects the different rays through different angles, so that they all converge at a common focal point.
DIF: Easy REF: Section 6.1
MSC: Understanding
OBJ: Compare and contrast the design, construction, and optical characteristics of reflecting and refracting telescopes.
Explain why stars twinkle when viewed from the ground. Would they twinkle if they were viewed from outer space?
ANS: Slight differences in air temperature cause density differences in the air which change optical densities. This causes light to refract slightly as it passes through different temperature regions. Atmospheric turbulence causes these regions to move over time, so two different beams of light will take slightly different paths over time. This causes a shimmering of objects viewed through Earth’s atmosphere. For telescopes like the Hubble Space Telescope, which lie above Earth’s atmosphere, this does not occur.
DIF: Easy REF: Section 6.1 MSC: Understanding
OBJ: Illustrate the effects of atmospheric seeing.
When a ray of light passes from vacuum into a material, what is the speed of light inside the material?
ANS: The speed of light in vacuum is always c. However, in a medium it is always lower by v = c/n, where n is the index of refraction of the material, and v is the speed of light in the medium.
DIF: Easy REF: Section 6.1 MSC: Remembering
OBJ: Illustrate the processes of reflection and refraction.
A ray of light is incident on a flat mirror at an angle of 15° degrees from the vertical, what is the angle of reflection, so the angle of reflection is also 15 degrees from the vertical.
ANS: The angle of incidence is equal to the angle of reflection.
DIF: Easy REF: Section 6.1
MSC: Remembering
OBJ: Illustrate the processes of reflection and refraction.
Explain how adaptive optics help compensate for atmospheric seeing.
ANS: Slight perturbances in the atmosphere can degrade the resolution of an image. Adaptive optics can measure these perturbances and correct for them before the light is imaged by bouncing it off a deformable mirror.
DIF: Medium REF: Section 6.1 MSC: Understanding
OBJ: Illustrate the effects of atmospheric seeing.
Explain why chromatic aberration is a problem for refracting lenses but not for reflecting mirrors.
ANS: Chromatic aberration occurs because refractors suffer dispersion caused the fact that the index of refraction of the lens depends on the wavelength of light going through it. As a result, different wavelengths of light will focus at different distances from a lens. Because the law of reflection holds for any wavelength, mirrors focus all wavelengths of light to the same focal point.
DIF: Medium REF: Section 6.1
MSC: Understanding
OBJ: Compare and contrast the design, construction, and optical characteristics of reflecting and refracting telescopes.
Label the eyepiece, lens, focus, and focal length of the telescope shown in the figure below.
ANS: This telescope is a refracting telescope. A student should label the eyepiece as the lens near the eye, the focus at the point where the light rays cross, the lens as the piece that initially bends the light from the stars, and the focal length as the distance between the lens and the focus.
DIF: Medium REF: Section 6.1
MSC: Remembering
OBJ: Compare and contrast the design, construction, and optical characteristics of reflecting and refracting telescopes.
In what way are Arecibo and the human eye similar?
ANS: They are similar because both gather electromagnetic energy, and they both have similar angular resolutions.
DIF: Medium REF: Section 6.1
MSC: Remembering
OBJ: Relate resolution to telescope design.
Label the eyepiece, primary mirror, secondary mirror, focus, and focal length of the telescope shown in the figure below.
ANS: This telescope is a reflecting telescope. A student should label the eyepiece as the lens near the eye, the focus at the point where the light rays cross, the primary mirror as the curved piece that initially reflects the light from the stars, the secondary mirror as the flat piece that reflects the light from the primary mirror to the eyepiece, and the focal length as the distance between the primary mirror and the focus. (NOTE: In this case, the focal length is not measured in a straight line!)
DIF: Difficult REF: Section 6.1
MSC: Remembering
OBJ: Compare and contrast the design, construction, and optical characteristics of reflecting and refracting telescopes.
Explain what happens when white light is refracted by a prism.
ANS: When white light is refracted by a prism, the path of the light is bent, twice. The amount of this bending (angle of refraction) is determined by (1) the index of refraction of the prism’s material, (2) the angle of incidence, and (3) the wavelength of the light (blue light is refracted more than red light in the same medium).
DIF: Difficult REF: Section 6.1 MSC: Understanding
OBJ: Illustrate the processes of reflection and refraction.
In 2009, the Cassini spacecraft made repeated orbits around Titan, Saturn’s largest moon. If this spacecraft orbited at an altitude of 1,000 km above Titan’s surface and its high-resolution camera had an angular resolution of 3 arcsec, how large an object could be resolved on Titan’s surface?
ANS: The small angle approximation says θ = 206,265 arcsec × D/d, where θ is the angular resolution of the camera, D is the diameter of the smallest resolvable surface feature on Titan, and d is the altitude of the spacecraft. Therefore, the smallest resolvable surface feature on Titan is D = (θ/206,265 arcsec) × d = (3 arcsec/206,265 arcsec) × 106 m = 15 m.
DIF: Difficult REF: Section 6.1 MSC: Applying
OBJ: Relate resolution to telescope design.
Calculate the resolution of an interferometric array consisting of five 10-m radio telescopes, each located 1,000 m apart from each other and observing a distant object at a wavelength of 21 cm.
ANS: θ = 2.06 × 105 × (l/D), where l = wavelength and D = dish separation. θ = 2.06 × 105 × (0.21 m/ 1000 m) arcsec = 43 arcsec.
DIF: Difficult REF: Section 6.1 MSC: Applying
OBJ: Relate resolution to telescope design.
What is the angular resolution of a 1-m, ground-based, optical telescope that observes at a wavelength of 600 nm compared to that of a 300-ft, single-dish radio telescope that observes at a wavelength of 21 cm?
ANS: The angular resolution of the 1-m, ground-based telescope is limited by the atmosphere to be approximately 1 arcsec. The angular resolution of the radio dish is given by its diffraction limit, which is θ = 2.06 × 105 × (21 cm/[300 × 12 in × 2.54 cm/1 in.]) arcsec = 473 arcsec. Therefore, the angular resolution of the optical telescope is about 500 times smaller than that of the radio telescope.
DIF: Difficult REF: Section 6.1 MSC: Applying
OBJ: Relate resolution to telescope design.
Explain three major advantages of CCDs over other imaging techniques.
ANS: These are possible answers: (1) they have much higher quantum efficiency (~80 percent); (2) their photometric response is linearly proportional to the number of photons they collect; (3) they yield output in digital format; (4) they cover a wide spectral range (optical through near-infrared).
DIF: Easy REF: Section 6.2 MSC: Remembering
OBJ: Relate the optical properties of the human eye to film or a CCD camera.
What is quantum efficiency?
ANS: Quantum efficiency determines how many responses occur for each photon received. A larger response to a photon means that a detector is more sensitive and can see fainter sources of light.
DIF: Easy REF: Section 6.2
MSC: Remembering
OBJ: Define the bold-faced vocabulary terms within the chapter.
When you look at the side of a CD where the data are stored, why do you observe a rainbow?
ANS: The closely spaced tracks of the CD act like a diffraction grating and disperse the light into its spectrum.
DIF: Easy REF: Section 6.2
MSC: Remembering
OBJ: Distinguish between imaging and spectroscopy.
Why is it difficult to view low-surface-brightness, such as the Andromeda Galaxy, with the naked eye? Does the view improve with the use of a telescope? What is needed to get a bright, clear view of the Andromeda Galaxy, as commonly seen in pictures?
ANS: The human eye has a low integration time. Using a telescope may increase the light-collecting area, but low surface brightness objects will still look dim. In order to get bright, clear images of such objects, photographic plates or CCDs must be used. With these detectors, the integration time can be increased, allowing more light to be collected for one image.
DIF: Medium REF: Section 6.2 MSC: Understanding
OBJ: Relate the optical properties of the human eye to film or a CCD camera.
Explain how a spectrograph works.
ANS: A spectrograph takes light from a telescope and disperses it into its constituent wavelengths with a prism or grating. The resulting spectrum is recorded (modern spectrographs use a CCD).
DIF: Medium REF: Section 6.2 MSC: Understanding
OBJ: Distinguish between imaging and spectroscopy.
Explain the difference between dispersion and diffraction. How can both phenomena be used to create a spectrum?
ANS: Dispersion is the wavelength dependence in refraction. Because blue light refracts more than red light, any white light that is refracted through a medium is dispersed into its spectral colors. Diffraction is distortion of a wavefront as it passes the edge of an opaque object. This is also wavelength dependent and can create a spectrum as white light passes through a pair of (or many) narrow slits. The resulting pattern is a mix of constructive and destructive interference patterns. Each wavelength will have its first maxima at a different location along the viewing screen, therefore showing a full spectrum.
DIF: Difficult REF: Section 6.2 MSC: Understanding
OBJ: Distinguish between imaging and spectroscopy.
Where is the best place to put a ground-based optical telescope? Discuss the reasons for your selection.
ANS: Mountaintops away from cities and in dry climates. This location gets your telescope away from light-pollution, as high above the atmosphere and water vapor as Earth’s surface can get. Also, finding a location that fits these requirements near the equator means you will be able to view the entire sky over the course of the year.
DIF: Medium REF: Section 6.3
MSC: Understanding
OBJ: Compare and contrast the practical utility of observing on the ground and from space for different wavelengths.
Name two reasons why astronomers might use a space telescope over a ground-based telescope.
ANS: (1) To observe at wavelengths other than visible and radio waves; (2) to avoid dealing with atmospheric distortion; (3) to avoid light-pollution on Earth; (4) to avoid weather on Earth.
DIF: Medium REF: Section 6.3 MSC: Remembering
OBJ: Compare and contrast the practical utility of observing on the ground and from space for different wavelengths.
Why don’t astronomers put all telescopes in space?
ANS: Building and launching a telescope into space is much more costly than building one on Earth. Also, the majority of space-based telescopes cannot be repaired when something breaks or updated as new technology becomes available.
DIF: Medium REF: Section 6.3 MSC: Understanding
OBJ: Compare and contrast the practical utility of observing on the ground and from space for different wavelengths.
Why does combining the light from smaller telescopes give observation results comparable to those of a single large telescope with a diameter equal to the separation of the two smaller telescopes?
ANS: An interferometric array will have the same angular resolution as a single-dish telescope with a diameter equal to the baseline separation of the individual telescopes in the interferometric array. However, it does not have the same light gathering power as a single larger telescope.
DIF: Medium REF: Section 6.3 MSC: Understanding
OBJ: Summarize the challenges and simplifications of observing in wavelengths other than optical.
Discuss two advantages of flyby missions over orbiters in exploring planets and moons in the solar system.
ANS: First, flyby missions are relatively inexpensive and are the easiest missions to design and execute. Second, they can visit several different planets and moons during their travels. DIF: Easy REF: Section 6.4 MSC: Remembering
OBJ: Evaluate the cost and benefit of different kinds of spacecraft (flyby, orbiter, lander, probe).
What are some advantages and disadvantages of using landers to explore the solar system?
ANS: Advantages are many. Landers allow us to study things that remote sensing cannot, for example, the composition of surfaces and the atmosphere. Some disadvantage are the cost, limited landing sites, and the applicability of the mission results limited to the landing site. It is impossible to study the planet or moon on a large scale.
DIF: Medium REF: Section 6.4 MSC: Remembering
OBJ: Evaluate the cost and benefit of different kinds of spacecraft (flyby, orbiter, lander, probe).
What are gravitational waves? Have astronomers been able to detect them yet?
ANS: Gravitational waves are disturbances in a gravitational field. Astronomers have yet to detect them but have strong theoretical evidence that suggests they exist.
DIF: Easy REF: Section 6.5 MSC: Understanding
OBJ: Establish why other tools (particle accelerators and detectors, supercomputers) are important to astronomy.
Discuss two tools that modern astronomers use to explore the cosmos that are different from traditional optical telescopes and give an example of how and why each is used.
ANS: These are possible answers: (1) radio telescopes— to record radio waves and, in interferometric arrays, to increase spatial resolution compared to single-dish radio telescopes; (2) adaptive optics—to obtain higher spatial resolution images by correcting for the blurring due to Earth’s atmosphere; (3) space-based telescopes—placed in orbit around Earth, provide high spatial resolution images because they are outside the blurring effects of Earth’s atmosphere; (4) airborne or high-flying observatories—can go outside Earth’s atmosphere and detect wavelengths of light such as infrared or microwave, which are absorbed by molecules in Earth’s atmosphere and do not reach the ground; (5) spacecraft—orbiters and landers can provide images with much better spatial resolution than Earth-based observations, and landers can physically probe the conditions on a planet’s or moon’s surface; (6) particle accelerators—smash atoms or particles together with high energy in order to explore their constituents and probe physical conditions similar to those of the early universe; (7) neutrino detectors—used to probe neutrinos emitted by astronomical objects, including the Sun; (8) gravitational wave detectors—measure gravitational waves in order to study changing gravitational fields such as those produced by merging binary stars; (9) high-speed computers—used to make predictions of complex physical processes, such as star formation or the evolution of the universe, that can be compared with observations to test theories.
DIF: Easy REF: Section 6.5
MSC: Remembering
OBJ: Establish why other tools (particle accelerators and detectors, supercomputers) are important to astronomy.
How much larger is the light-gathering power of a 10-inch telescope than the human eye?
ANS: Light-gathering power is proportional to the area of the aperture, which is proportional to the square of the diameter of the aperture. Thus, the light-gathering power of a 10-inch telescope is X times greater than your eye, where X = (10 in. × 2.54 cm/1 in.)2/(6 mm)2 = 645.
DIF: Easy REF: Working It Out 6.1
MSC: Applying
OBJ: Compute the magnification and light-collecting areas of different optical systems.
What is the diffraction limit of a 4-m telescope observing at a wavelength of 650 nm?
ANS: θ = 2.06 × 105 × (6.50 × 107 m/4m) arcsec = 0.033 arcsec.
DIF: Difficult REF: Working It Out 6.2 MSC: Applying
OBJ: Compute the diffraction limits of different optical systems.
Chapter 7: The Birth and Evolution of Planetary Systems
Learning Objectives
Define the bold-faced vocabulary terms within the chapter.
Multiple Choice: 1, 2, 4, 8, 16, 17, 27, 28, 29, 42
Short Answer: 4
7.1 Planetary Systems Form around a Star
Illustrate the nebular hypothesis for solar system formation.
Multiple Choice: 5
Short Answer: 1, 2
Describe how astronomers and geologists arrived at the same conclusions about Earth’s origins from different pieces of evidence.
Multiple Choice: 3
Short Answer: 3
7.2 The Solar System Began with a Disk
Explain conservation of angular momentum.
Multiple Choice: 9, 11, 13
Short Answer: 7
Illustrate how accretion disks transfer angular momentum so that stars and planets can collapse.
Multiple Choice: 10, 12, 14, 15
Short Answer: 5, 6
Describe the formation sequence of planetesimals in an accretion disk.
Multiple Choice: 6, 7
7.3 The Inner Disk and Outer Disk Formed at Different Temperatures
Explain conservation of energy.
Multiple Choice: 18, 21
Use conservation of energy to argue why material falling on an accretion disk heats the disk up.
Multiple Choice: 24, 25
Short Answer: 10, 12
Distinguish between refractory and volatile materials.
Multiple Choice: 22
Short Answer: 8
Relate the temperature of an accretion disk to the presence of different types of materials (e.g. refractory, volatile, organic, ice) within the disk.
Multiple Choice: 23, 26
Short Answer: 14
Compare and contrast primary and secondary atmospheres.
Multiple Choice: 19, 20
Short Answer: 9, 11, 13
7.4 The Formation of Our Solar System
Compare and contrast terrestrial and giant planets.
Multiple Choice: 31, 40
Describe how planetesimals become planets.
Multiple Choice: 32, 33, 34, 35, 37, 38, 39
Short Answer: 15, 16, 17, 18
Show how temperature differences in our accretion disk led to the formation of terrestrial and giant planets.
Multiple Choice: 30, 36
7.5 Planetary Systems Are Common
Summarize the five methods that astronomers use to detect extrasolar planets.
Multiple Choice: 41, 43, 44, 45, 46, 47, 48, 50, 51, 52, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65
Short Answer: 19, 20, 21, 22, 23, 24, 25, 26, 28, 29
Describe how planetary migration accounts for hot Jupiters being located very close to their host stars.
Multiple Choice: 49, 53, 54
Short Answer: 27
Working It Out 7.1
Compute and compare orbital and spin angular momentum.
Multiple Choice: 66, 67, 68, 69
Short Answer: 30
Working It Out 7.2
Use Kepler’s third law to calculate the size of a planet’s orbit.
Working It Out 7.3
Estimate the size of a planet by considering how much of its parent star’s light it occults.
Multiple Choice: 70
MULTIPLE CHOICE
What is a protostar?
a planet like Jupiter
a hot star
a large ball of gas not yet hot enough at its core to be a star
a large ball of gas too hot at its core to be a star
a star with too much angular momentum
ANS: C DIF: Easy REF: Section 7.1
MSC: Remembering
OBJ: Define the bold-faced vocabulary terms within the chapter.
What is a meteorite?
a streak of light in the sky
a rock that fell to Earth from space
a fireball
a volcanic rock
an iron-rich rock
ANS: B DIF: Easy REF: Section 7.1
MSC: Remembering
OBJ: Define the bold-faced vocabulary terms within the chapter.
What have astronomers and geologists studied to arrive at the same conclusions about Earth’s origins?
volcanism in the solar system
comets
meteorites
the Moon
the oceans
ANS: C DIF: Easy REF: Section 7.1
MSC: Remembering
OBJ: Describe how astronomers and geologists arrived at the same conclusions about Earth’s origins from different pieces of evidence.
The icy planetesimals that remain in the solar system today are called
asteroids.
moons.
meteorites.
comet nuclei.
ANS: D DIF: Easy REF: Section 7.1
MSC: Remembering
OBJ: Define the bold-faced vocabulary terms within the chapter.
Which of the following is not a characteristic of the early Solar System, based on current observations?
The early solar nebula must have been flattened.
The material from which the planets formed was swirling about the Sun in the same average rotational direction.
The first objects to form started out small and grew in size over time.
The initial composition of the solar nebula varied between its inner and outer regions.
Temperatures decreased with increasing distance from the Sun.
ANS: D DIF: Medium REF: Section 7.1
MSC: Remembering
OBJ: Illustrate the nebular hypothesis for solar system formation.
The smallest grains of dust stick together in an accretion disk by which force?
gravitational force
electrostatic force
magnetic force
quantum mechanical force
strong force
ANS: B DIF: Medium REF: Section 7.2
MSC: Remembering
OBJ: Describe the formation sequence of planetesimals in an accretion disk.
In order for two clumps of dust to stick together in an accretion disk, they must collide at roughly
100 m/s.
10 m/s.
1 m/s.
0.5 m/s.
0.1 m/s or less.
ANS: E DIF: Medium REF: Section 7.2
MSC: Remembering
OBJ: Describe the formation sequence of planetesimals in an accretion disk.
What is a planetesimal?
bodies of ice and rock 100 meters or more in diameter
bodies of ice and rock 10 meters or less in diameter
bodies of ice and rock about 1 meter in diameter
another name for dwarf planets
planets that haven’t cleared their orbits
ANS: A DIF: Easy REF: Section 7.2
MSC: Remembering
OBJ: Define the bold-faced vocabulary terms within the chapter.
According to the conservation of angular momentum, if an ice-skater who is spinning with her arms out wide slowly pulls them close to her body, this will cause her to . . .
spin faster.
spin slower.
maintain a constant rate of spin.
fall down.
ANS: A DIF: Easy REF: Section 7.2
MSC: Understanding
OBJ: Explain conservation of angular momentum.
Approximately how much mass was there in the protoplanetary disk out of which the planets formed, compared to the mass of the Sun?
50 percent
25 percent
10 percent
5 percent
< 1 percent
ANS: E DIF: Medium REF: Section 7.2
MSC: Remembering
OBJ: Illustrate how accretion disks transfer angular momentum so that stars and planets can collapse.
In the figure shown below, the direction of the disk’s rotation is indicated. What is the direction of the protostellar Sun’s rotation?
impossible to tell
in the opposite direction as the disk’s rotation
in the same direction as the disk’s rotation
perpendicular to the disk’s rotation
ANS: C DIF: Medium REF: Section 7.2
MSC: Understanding
OBJ: Explain conservation of angular momentum.
Consider the figure shown below. At which point in time does the collapsing cloud have the greatest angular momentum?
1
2
3
1 and 2, because the protostar has not yet formed
The cloud has the same angular momentum at each point in time.
ANS: E DIF: Medium REF: Section 7.2
MSC: Understanding
OBJ: Illustrate how accretion disks transfer angular momentum so that stars and planets can collapse.
The fact that Jupiter’s radius is contracting at a rate of 1 mm per year results in
Jupiter’s rotation rate slowing down with time.
Jupiter’s shape being noticeably oblate.
Jupiter moving slightly farther from the Sun with time.
Jupiter radiating more heat than it receives from the Sun.
Jupiter having a strong magnetic field.
ANS: D DIF: Difficult REF: Section 7.2
MSC: Applying
OBJ: Explain conservation of angular momentum.
If a collapsing interstellar cloud formed only a protostar without an accretion disk around it, what would happen?
The forming protostar would be significantly less massive than it would have been otherwise.
The forming protostar would be rotating too fast to hold itself together.
Only giant planets would form around the protostar.
Only terrestrial planets would form around the protostar.
More planets would form around the protostar.
ANS: B DIF: Difficult REF: Section 7.2
MSC: Remembering
OBJ: Illustrate how accretion disks transfer angular momentum so that stars and planets can collapse.
Conservation of angular momentum slows a cloud’s collapse
equally in all directions.
only when the cloud is not rotating initially.
mostly along directions perpendicular to the cloud’s axis of rotation.
mostly at the poles that lie along the cloud’s axis of rotation.
to a complete stop.
ANS: C DIF: Difficult REF: Section 7.2
MSC: Understanding
OBJ: Illustrate how accretion disks transfer angular momentum so that stars and planets can collapse.
What is a primary atmosphere?
the atmospheres that all planets have today
the gas captured during the planet’s formation
the gas captured after the planet’s formation
the oxygen and nitrogen in Earth’s atmosphere
the gas closest to the planet’s surface
ANS: B DIF: Easy REF: Section 7.3
MSC: Remembering
OBJ: Define the bold-faced vocabulary terms within the chapter.
What is a secondary atmosphere?
the atmosphere that escapes
the gas captured during the planet’s formation
the gas farthest from the surface
the atmosphere that remains after the planet has formed
the gas closest to the planet surface
ANS: D DIF: Easy REF: Section 7.3
MSC: Remembering
OBJ: Define the bold-faced vocabulary terms within the chapter.
Consider four spheres of equal mass and size. Which has the most potential energy?
a sphere on the top shelf of a bookshelf
a sphere rolling on the floor at the base of the bookshelf
a sphere sitting at rest on the floor at the base of the bookshelf
a sphere on the middle shelf of a bookshelf
a sphere that fell from the top shelf to the floor
ANS: A DIF: Easy REF: Section 7.3
MSC: Applying
OBJ: Explain conservation of energy.
The atmosphere of which of these Solar System bodies is primary, as opposed to secondary, in origin?
Venus
Earth
Saturn’s moon Titan
Saturn
Mars
ANS: D DIF: Easy REF: Section 7.3
MSC: Remembering
OBJ: Compare and contrast primary and secondary atmospheres.
The primary atmospheres of the planets are made mostly of
carbon and oxygen.
hydrogen and helium.
oxygen and nitrogen.
iron and nickel.
nitrogen and argon.
ANS: B DIF: Easy REF: Section 7.3
MSC: Remembering
OBJ: Compare and contrast primary and secondary atmospheres.
When you push your palms together and rub them back and forth, you are demonstrating one way of converting _________ energy into _________ energy.
potential; thermal
kinetic; potential
thermal; kinetic
kinetic; thermal
potential; total
ANS: D DIF: Easy REF: Section 7.3
MSC: Applying
OBJ: Explain conservation of energy.
The solid form of a volatile material is generally referred to as a(n)
metal.
silicate.
ice.
rock.
refractory material.
ANS: C DIF: Easy REF: Section 7.3
MSC: Remembering
OBJ: Distinguish between refractory and volatile materials.
Based on the figure shown below, which planet(s) is(are) most likely to have the largest fraction of its(their) mass made of highly volatile materials such as methane and ammonia?
Venus, Earth, and Mars
Earth
Saturn
Jupiter
Uranus
ANS: E DIF: Medium REF: Section 7.3
MSC: Applying
OBJ: Relate the temperature of an accretion disk to the presence of different types of materials (e.g., refractory, volatile, organic, ice) within the disk.
What happens to the kinetic energy of gas as it falls toward and eventually hits the accretion disk surrounding a protostar?
It is immediately converted into photons, giving off a flash of light on impact.
It is converted into thermal energy, heating the disk.
It is converted into potential energy as the gas plows through the disk and comes out the other side.
It becomes the kinetic energy of the orbit of the gas in the accretion disk around the protostar.
It disappears into interstellar space.
ANS: B DIF: Medium REF: Section 7.3
MSC: Applying
OBJ: Use conservation of energy to argue why material falling on an accretion disk heats the disk up.
What sets the temperature of the pocket of gas in a protoplanetary disk?
its distance from the forming star
how much kinetic energy was converted to heat
how much radiation from the forming star shines on the gas
a combination of A, B, and C
ANS: D DIF: Medium REF: Section 7.3
MSC: Applying
OBJ: Use conservation of energy to argue why material falling on an accretion disk heats the disk up.
Whether or not a planet is composed mostly of rock or gas is set by
its mass.
its temperature.
its distance from the star when it formed.
a combination of A, B, and C
ANS: D DIF: Difficult REF: Section 7.3
MSC: Applying
OBJ: Relate the temperature of an accretion disk to the presence of different types of materials (e.g., refractory, volatile, organic, ice) within the disk.
Which of the following is a terrestrial planet?
Mercury
Jupiter
Venus
both A and B
both A and C
ANS: E DIF: Easy REF: Section 7.4
MSC: Remembering
OBJ: Define the bold-faced vocabulary terms within the chapter.
Which of the following is a giant planet?
Mercury
Jupiter
Venus
both A and B
both A and C
ANS: B DIF: Easy REF: Section 7.4
MSC: Remembering
OBJ: Define the bold-faced vocabulary terms within the chapter.
Which is the best description of a moon?
any small icy body in the solar system
any small rocky body in the solar system
any natural satellite of a planet or asteroid
a captured asteroid
a captured comet
ANS: C DIF: Easy REF: Section 7.4
MSC: Remembering
OBJ: Define the bold-faced vocabulary terms within the chapter.
What is the most important factor in determining whether or not a planet will be rocky like terrestrial planets or gaseous like giant planets?
the time at which the planet forms
the planet’s radius
the planet’s distance from the Sun
whether the planet has moons
the planet’s internal temperature
ANS: C DIF: Easy REF: Section 7.4
MSC: Applying
OBJ: Show how temperature differences in our accretion disk led to the formation of terrestrial and giant planets.
Why do the outer giant planets have massive gaseous atmospheres of hydrogen and helium whereas the inner planets do not?
These gases were more abundant in the outer regions of the accretion disk where the outer planets formed.
The outer planets grew massive quickly enough to gravitationally hold on to these gases before the solar wind dispersed the accretion disk.
The inner planets are made of rock.
Frequent early collisions by comets with the inner planets caused most of their original atmospheres to dissipate.
ANS: B DIF: Easy REF: Section 7.4
MSC: Understanding
OBJ: Compare and contrast terrestrial and giant planets.
Comets and asteroids are
other names for moons of the planets.
primarily located within 1 astronomical unit (AU) of the Sun.
all more massive than Earth’s Moon.
material left over from the formation of the planets.
other names for meteors.
ANS: D DIF: Easy REF: Section 7.4
MSC: Remembering
OBJ: Describe how planetesimals become planets.
The Moon probably formed
out of a collision between Earth and a Mars-sized object.
when Earth’s gravity captured a planetesimal.
when the accretion disk around Earth fragmented.
when planetesimals collided to form a more massive object.
when a piece of Earth broke off and entered orbit.
ANS: A DIF: Easy REF: Section 7.4
MSC: Applying
OBJ: Describe how planetesimals become planets.
What prevented the Moon from maintaining any atmosphere with which it originally formed?
It repeatedly collided with planetesimals.
It is too close to the Sun.
The solar wind blew it away.
It is not massive enough.
It is tidally locked to Earth.
ANS: D DIF: Medium REF: Section 7.4
MSC: Applying
OBJ: Describe how planetesimals become planets.
Which of the following is not considered evidence of cataclysmic impacts in the history of our Solar System?
Uranus is “tipped over” so that it rotates on its side.
Valles Marineris on Mars is a huge scar, many times deeper than the Grand Canyon, which spans one-fourth the circumference of the planet.
Mercury has a crust that has buckled on the opposite side of an impact crater.
Mimas has a crater whose diameter is roughly one-third of the Moon’s size.
Mercury, Earth’s Moon, and many other small bodies are covered with many impact craters.
ANS: B DIF: Medium REF: Section 7.4
MSC: Remembering
OBJ: Describe how planetesimals become planets.
The difference in composition between the giant planets and the terrestrial planets is most likely caused by the fact that
the giant planets are much larger.
only the terrestrial planets have iron cores.
the terrestrial planets are closer to the Sun.
the giant planets are made mostly of carbon.
only small differences in chemical composition existed in the solar nebula.
ANS: C DIF: Medium REF: Section 7.4
MSC: Applying
OBJ: Show how temperature differences in our accretion disk led to the formation of terrestrial and giant planets.
Two competing models of the formation of giant gaseous planets suggest they form either from gas accreting onto a rocky core or from
fragmentation of the accretion disk that surrounds the protostar.
the merger of two large planetesimals.
planets stolen from another nearby protostar.
materials condensing out of the solar wind.
an eruption of material from the protostar.
ANS: A DIF: Medium REF: Section 7.4
MSC: Remembering
OBJ: Describe how planetesimals become planets.
Was it ever possible (or is it currently possible) for Jupiter to become a star?
Yes, it is in the process of becoming a star in the near future.
Yes, but it cooled off before it could become a star.
No, it would have to be at least 13 times more massive.
No, its composition is too different from stars for it to become one.
No, it used to be massive enough, but the solar wind has blown off too much of its mass.
ANS: C DIF: Medium REF: Section 7.4
MSC: Applying
OBJ: Describe how planetesimals become planets.
How much material in an accretion disk goes into forming the planets, moons, and smaller objects?
most of it
roughly half of it
none; these objects were not formed in the accretion disk
a small amount of it
ANS: D DIF: Medium REF: Section 7.4
MSC: Remembering
OBJ: Describe how planetesimals become planets.
Why do the terrestrial planets have a much higher fraction of their mass in heavy chemical elements (as opposed to lighter chemical elements) than the giant planets?
Terrestrial planets are low in mass and high in temperature, thus their lighter chemical elements eventually escaped to the outer reaches of the Solar System.
The heavier elements in the forming solar nebula sank to the center of the Solar System, thus the inner terrestrial planets formed mostly from heavy chemical elements.
The giant planets were more massive than terrestrial planets, and the giant planets preferentially pulled the lighter elements from the inner to the outer Solar System.
Terrestrial planets formed much earlier than giant planets before the hydrogen and helium had a chance to cool and condense onto them.
Terrestrial planets are colder and thus more massive chemical elements condensed on them than on the giant planets.
ANS: A DIF: Difficult REF: Section 7.4
MSC: Applying
OBJ: Compare and contrast terrestrial and giant planets.
Which property of an extrasolar planet cannot be determined using the Doppler effect?
orbital period
orbital distance
orbital speed
mass
radius
ANS: E DIF: Easy REF: Section 7.5
MSC: Remembering
OBJ: Summarize the five methods that astronomers use to detect extrasolar planets.
What is the habitable zone?
the distance from a star where liquid water can exist
the location on the sky where planets can be found
the distance from a star where liquid can exist
the distance from a star where planets have oxygen in the atmosphere
1 AU from any star
ANS: A DIF: Easy REF: Section 7.5
MSC: Remembering
OBJ: Define the bold-faced vocabulary terms within the chapter.
Which method can be used to determine the radius of an extrasolar planet?
Doppler shift
transit
microlensing
direct imaging
none of the above
ANS: B DIF: Easy REF: Section 7.5
MSC: Remembering
OBJ: Summarize the five methods that astronomers use to detect extrasolar planets.
Most planets currently found around other stars are
rocky in composition like terrestrial planets.
2 to 10 MEarth, which is smaller than Neptune.
2 to 10 MJupiter.
located at distances much larger than Jupiter’s distance from the Sun.
similar in mass to Earth.
ANS: B DIF: Easy REF: Section 7.5
MSC: Remembering
OBJ: Summarize the five methods that astronomers use to detect extrasolar planets.
Which is not a scientific goal of NASA’s Kepler mission?
finding Earth-sized planets
finding rocky planets
finding Earth-sized planets that could have liquid water
finding intelligent life on other planets
All the above are goals of the Kepler mission
ANS: D DIF: Easy REF: Section 7.5
MSC: Applying
OBJ: Summarize the five methods that astronomers use to detect extrasolar planets.
Consider a star that is more massive and hotter than the Sun. For such a star, the habitable zone would
be located inside 1 AU.
be located outside 1AU.
not exist at any radii.
exist at every radii.
ANS: B DIF: Easy REF: Section 7.5
MSC: Applying
OBJ: Summarize the five methods that astronomers use to detect extrasolar planets.
The Kepler mission is designed to search for extrasolar planets using the _________ method.
Doppler shift
transit
microlensing
direct imaging
ANS: B DIF: Easy REF: Section 7.5
MSC: Remembering
OBJ: Summarize the five methods that astronomers use to detect extrasolar planets.
Earth-sized planets have been found using the _________ method(s).
Doppler shift
transit and Doppler shift
microlensing
direct imaging
transit
ANS: B DIF: Medium REF: Section 7.5
MSC: Remembering
OBJ: Summarize the five methods that astronomers use to detect extrasolar planets.
Astronomers believe that the “hot Jupiters” found orbiting other stars must have migrated inward over time
by slowly accreting large amounts of gas and increasing their gravitational pull.
by losing their gas because of evaporation.
by losing orbital angular momentum.
after colliding with another planet.
after a close encounter between their star and another star.
ANS: C DIF: Medium REF: Section 7.5
MSC: Applying
OBJ: Describe how planetary migration accounts for hot Jupiters being located very close to their host stars.
The borderline between the most massive planet and the least massive brown dwarf occurs at
4 Jupiter masses.
13 Jupiter masses.
120 Jupiter masses.
80 Jupiter masses.
45 Jupiter masses.
ANS: B DIF: Medium REF: Section 7.5
MSC: Remembering
OBJ: Summarize the five methods that astronomers use to detect extrasolar planets.
Have astronomers detected any Earth-sized planets around normal stars yet?
Yes, the Kepler spacecraft is just starting to find them.
Yes, although the ones detected lie much closer to their stars than we do to ours.
Yes, although the ones detected lie much farther from their stars than we do from ours.
No, we do not have the technology to detect such low-mass planets yet.
No; although we have the technology to detect low-mass planets, we haven’t found any others yet.
ANS: A DIF: Medium REF: Section 7.5
MSC: Applying
OBJ: Summarize the five methods that astronomers use to detect extrasolar planets.
Why have astronomers using the radial velocity method found more Jupiter-sized planets at a distance of 1 AU around other stars than Earth-sized planets?
A Jupiter-sized planet occults a larger area than an Earth-sized planet.
A Jupiter-sized planet exerts a larger gravitational force on the star than an Earth-sized planet, and the Doppler shift of the star is larger.
A Jupiter-sized planet shines brighter than an Earth-sized planet.
Earth-sized planets are much rarer than Jupiter-sized planets.
Actually, the planets found at these distances all have been Earth-sized.
ANS: B DIF: Medium REF: Section 7.5
MSC: Understanding
OBJ: Summarize the five methods that astronomers use to detect extrasolar planets.
When astronomers began searching for extrasolar planets, they were surprised to discover Jupiter-sized planets much closer than 1 AU from their parent stars. Why is this surprising?
These planets must have formed at larger radii where temperatures were cooler and then migrated inward.
Jupiter-sized, rocky planets were thought to be uncommon in other solar systems.
These planets must be the remnants of failed stars.
Earth-like planets must be rarer than Jupiter-sized planets in other solar systems.
Jupiter-sized planets so close to the star are different than in our Solar System.
ANS: A DIF: Medium REF: Section 7.5
MSC: Applying
OBJ: Describe how planetary migration accounts for hot Jupiters being located very close to their host stars.
Which of the following is false?
Hundreds of extrasolar planets have been discovered to date from radial velocity surveys.
The most common types of extrasolar planets found to date have masses 10 times the mass of Jupiter and lie within 5 AU from their parent star.
Some planetary systems have been found that contain multiple planets.
A star can brighten significantly because of gravitational lensing when a planet that orbits it passes directly in front of the star.
The Kepler mission has begun to find terrestrial planets similar in size to Earth.
ANS: B DIF: Medium REF: Section 7.5
MSC: Applying
OBJ: Describe how planetary migration accounts for hot Jupiters being located very close to their host stars.
Astronomers have used radial velocity monitoring to discover
extrasolar planetary systems that are similar to our own Solar System.
Earth-sized planets around other stars.
Earth-sized planets at distances of 10 AU from their parent stars.
extrasolar planetary systems that contain more than one planet.
all of the above
ANS: D DIF: Medium REF: Section 7.5
MSC: Applying
OBJ: Summarize the five methods that astronomers use to detect extrasolar planets.
An observer located outside our Solar System, who monitors the velocity of our Sun over time, will find that the Sun’s velocity varies by ± 12 m/s over a period of 12 years, due to
Jupiter’s gravitational pull.
Earth’s gravitational pull.
variations in its brightness.
convection on the Sun’s surface.
the sunspot cycle.
ANS: A DIF: Medium REF: Section 7.5
MSC: Understanding
OBJ: Summarize the five methods that astronomers use to detect extrasolar planets.
Detecting a planet around another star using the transit method is difficult because the
planet must pass directly in front of the star.
planet must have a rocky composition.
star must be very dim.
star must be moving with respect to us.
planet’s orbital period is usually longer than 1 month.
ANS: A DIF: Medium REF: Section 7.5
MSC: Applying
OBJ: Summarize the five methods that astronomers use to detect extrasolar planets.
In the figure below, which of the dips in the brightness of the star is(are) caused by the transit of the planet with the largest orbital period?
A
B
C
A and B
B and C
ANS: C DIF: Medium REF: Section 7.5
MSC: Applying
OBJ: Summarize the five methods that astronomers use to detect extrasolar planets.
Figure 7.4 shows data from the transit study of a star in which three different planets repeatedly transit in front of the star (A, B, and C). Which dip is(are) caused by the transit of the planet with the smallest radius?
A
B
C
A, B, and C
impossible to tell from these data
ANS: A DIF: Medium REF: Section 7.5
MSC: Applying
OBJ: Summarize the five methods that astronomers use to detect extrasolar planets.
Using the Doppler effect data shown in the figure below, determine the approximate orbital period of the extrasolar planet.
1 year
3 years
6 years
8 years
12 years
ANS: C DIF: Medium REF: Section 7.5
MSC: Applying
OBJ: Summarize the five methods that astronomers use to detect extrasolar planets.
Using the Doppler effect data for a particular star shown in Figure 7.5 and assuming the star is about the same mass as our Sun, determine the approximate orbital distance of its exoplanet.
1.1 AU
6.4 AU
18 AU
36 AU
3.3 AU
ANS: E DIF: Difficult REF: Section 7.5
MSC: Applying
OBJ: Summarize the five methods that astronomers use to detect extrasolar planets.
From the data shown in Figure 7.5, which property of an extrasolar planet cannot be determined?
orbital period
orbital distance
radius
mass
All of the above properties can be determined.
ANS: C DIF: Difficult REF: Section 7.5
MSC: Applying
OBJ: Summarize the five methods that astronomers use to detect extrasolar planets.
What is the best method to detect Earth-sized exoplanets with the telescopes and instrumentation that exist today?
Doppler shift
Transit
Microlensing
Direct imaging
ANS: B DIF: Difficult REF: Section 7.5
MSC: Remembering
OBJ: Summarize the five methods that astronomers use to detect extrasolar planets.
Which of the following is false?
The masses of exoplanets can be determined using the radial velocity technique.
Most of the exoplanets detected to date have masses that are between 2 and 10 MEarth.
Some exoplanets have been found in the habitable zone around their stars.
Using the transit technique, the Kepler satellite has detected rocky planets.
No images of exoplanets have been obtained because they are too far away.
ANS: E DIF: Difficult REF: Section 7.5
MSC: Applying
OBJ: Summarize the five methods that astronomers use to detect extrasolar planets.
In the figure shown below, what can be directly measured from the information given?
the mass of the planet
percentage reduction in light
size of the planet
orbital radius of the planet
distance of the star
ANS: B DIF: Difficult REF: Section 7.5
MSC: Understanding
OBJ: Summarize the five methods that astronomers use to detect extrasolar planets.
What is the ratio of the orbital angular momentum of Earth compared to its spin angular momentum? Note that Earth has a radius of 6 × 106 m, and 1 AU is 1.5 × 1011 m.
1
70
640
25,000
4.3 × 106
ANS: E DIF: Difficult REF: Working It Out 7.1
MSC: Applying
OBJ: Compute and compare orbital and spin angular momentum.
What is the ratio of the orbital angular momentum of Jupiter to its spin angular momentum? Jupiter’s orbit has a semimajor axis of 5 AU and period of 12 years, and Jupiter has a rotation period of 0.4 day and a radius of 70,000 km.
650,000
26,000
920
38
4.5
ANS: B DIF: Difficult REF: Working It Out 7.1
MSC: Applying
OBJ: Compute and compare orbital and spin angular momentum.
If an interstellar cloud having a diameter of 1016 m and a rotation period of 1 million years were to collapse to form a sphere that had the diameter of our Solar System, approximately 40 AU, what would its rotation period be? Assume the cloud’s total mass and angular momentum did not change.
1 million years
600 years
1 year
6 years
4 months
ANS: E DIF: Difficult REF: Working It Out 7.1
MSC: Applying
OBJ: Compute and compare orbital and spin angular momentum.
Consider a small parcel of gas in the cloud out of which the Sun formed that initially was located in the accretion disk at a distance of 10 AU from the Sun and rotating around it with a speed of 10 km/s. If this parcel of gas eventually found its way to a distance of 1 AU from the Sun without changing its orbital angular momentum, what would be its new rotation speed?
100 km/s
0.1 km/s
0.001 km/s
10 km/s
1,000 km/s
ANS: A DIF: Difficult REF: Working It Out 7.1
MSC: Applying
OBJ: Compute and compare orbital and spin angular momentum.
If an astronomer on a planet orbiting a nearby star observed the Sun when Neptune was transiting in front of the Sun, how would the Sun’s brightness change? Note that the radius of Neptune is 2.5 × 107 m.
The Sun’s brightness would decrease by 0.1 percent.
The Sun’s brightness would increase by 0.1 percent.
The Sun’s brightness would increase by 1 percent.
The Sun’s brightness would decrease by 1 percent.
The Sun’s brightness would not change at all.
ANS: A DIF: Difficult REF: Working It Out 7.3
MSC: Applying
OBJ: Estimate the size of a planet by considering how much of its parent star’s light it occults.
SHORT ANSWER
Explain the nebular hypothesis, and describe two observations that support it.
ANS: In the nebular hypothesis, a rotating cloud of interstellar gas collapsed and flattened to form a disk from which the Sun and planets formed. The observation of disks around protostars and young stars provides evidence in support of this idea, as does the fact that all planets orbit the Sun in the same direction.
DIF: Easy REF: Section 7.1 MSC: Understanding
OBJ: Illustrate the nebular hypothesis for solar system formation.
Explain why astronomers believe that the formation of planets is a natural by-product of star formation.
ANS: To explain the structure of the solar system (the direction and inclination of planetary orbits), astronomers believe that planets must form out of disks of material. These disks would bear a striking resemblance to disks that have been observed around a number of young stars.
DIF: Easy REF: Section 7.1 MSC: Understanding
OBJ: Illustrate the nebular hypothesis for solar system formation.
How do meteorites tell us about how the solar system formed?
ANS: Studying meteorites can tell us about the chemical composition of the solar nebula, as well as the process of planetesimal formation. Some meteorites show a clumpy, nonuniform, composition similar to concrete. This leads astronomers and geologist to conclude that small things stuck together to grow larger and form planetesimals.
DIF: Difficult REF: Section 7.1 MSC: Understanding
OBJ: Describe how astronomers and geologists arrived at the same conclusions about Earth’s origins from different pieces of evidence.
What does conservation of angular momentum mean?
ANS: It means the angular momentum of a system cannot be changed via internal forces; it can be changed only by external forces.
DIF: Easy REF: Section 7.2 MSC: Understanding
OBJ: Define the bold-faced vocabulary terms within the chapter.
What evidence do we have that the accretion disk that formed the Solar System was initially much more dense near its center?
ANS: The Sun contains 99 percent of all the mass of the Solar System.
DIF: Easy REF: Section 7.2 MSC: Applying
OBJ: Illustrate how accretion disks transfer angular momentum so that stars and planets can collapse.
Explain why an accretion disk forms around a protostar when an interstellar cloud collapses.
ANS: As the cloud collapses, the rate of rotation increases so that it halts the collapse of the cloud toward its axis of rotation, but not parallel to its axis of rotation.
DIF: Medium REF: Section 7.2 MSC: Understanding
OBJ: Illustrate how accretion disks transfer angular momentum so that stars and planets can collapse.
What happens to a slowly rotating cloud as it collapses to form a stellar system?
ANS: Due to the conservation of momentum, the cloud’s rotation increases, eventually flattening into an accretion disk.
DIF: Medium REF: Section 7.2 MSC: Remembering
OBJ: Explain conservation of angular momentum.
What is the difference between refractory and volatile materials?
ANS: Refractory materials are capable of withstanding high temperatures without melting or being vaporized, whereas volatile materials are not.
DIF: Easy REF: Section 7.3 MSC: Remembering
OBJ: Distinguish between refractory and volatile materials.
Explain why there are significant amounts of methane and ammonia in the atmospheres of Uranus and Neptune but not nearly as much in the atmospheres of Jupiter and Saturn.
ANS: Ammonia and methane are volatile materials that are only found in the far outer Solar System where temperatures are very low. At the radii of Jupiter and Saturn, the nebula was hotter than that at Uranus and Neptune, which are farther from the Sun.
DIF: Medium REF: Section 7.3 MSC: Applying
OBJ: Compare and contrast primary and secondary atmospheres.
Why does an accretion disk heat up?
ANS: As material falls onto the disk, gravitational potential energy is converted to kinetic energy. The kinetic is converted to thermal energy when the material collides with other material in the disk.
DIF: Medium REF: Section 7.3 MSC: Remembering
OBJ: Use conservation of energy to argue why material falling on an accretion disk heats the disk up.
The primary atmosphere of Earth consisted of what type of chemical elements and from where did it originate? What chemical elements did the secondary atmosphere of Earth consist of and from where did it originate?
ANS: The primary atmosphere consisted mostly of hydrogen and helium, similar to the material that formed the solar nebula. The secondary atmosphere of Earth consisted mostly of carbon dioxide that was outgassed from the interior due to volcanic activity
DIF: Medium REF: Section 7.3
MSC: Remembering
OBJ: Compare and contrast primary and secondary atmospheres.
Explain the primary reasons why the inner solar nebula was hotter than the outer solar nebula.
ANS: The inner solar nebula was hotter than the outer solar nebula because the inner regions converted more of their potential energy into kinetic energy and heat when the original cloud collapsed to form the Solar System. In addition, when the Sun began to shine, it heated the inner Solar System more than the outer Solar System.
DIF: Medium REF: Section 7.3
MSC: Understanding
OBJ: Use conservation of energy to argue why material falling on an accretion disk heats the disk up.
Why did the terrestrial planets lose their primary atmospheres?
ANS: The planets have too little mass and therefore too little gravitational force to keep in the hot light gases that were present in the protoplanetary disk.
DIF: Medium REF: Section 7.3
MSC: Remembering
OBJ: Compare and contrast primary and secondary atmospheres.
How do astronomers explain the basic difference in composition between the inner planets and the outer planets?
ANS: The inner planets (Mercury, Venus, Earth, and Mars) formed in the region of the Solar System where only refractory materials could exist in solid form, therefore they are composed mostly of rocks and metals. The outer planets (Jupiter, Saturn, Uranus, and Neptune) formed out where even volatile materials could exist in solid form. As a result, in addition to rocks and metals, the Jovian planets and their moons are largely composed of ices as well. The solar wind reinforced these differences by clearing the inner Solar System of light gases during the planetary formation process.
DIF: Medium REF: Section 7.3
MSC: Understanding
OBJ: Relate the temperature of an accretion disk to the presence of different types of materials (e.g., refractory, volatile, organic, ice) within the disk.
Why did the planetesimals in the asteroid belt never coalesce into a planet?
ANS: The gravity of Jupiter was so strong that the material could not coalesce.
DIF: Easy REF: Section 7.4 MSC: Understanding
OBJ: Describe how planetesimals become planets.
Why might a newly discovered comet contain clues to the composition of the early solar nebula?
ANS: Comets are believed to be made of ice and dust similar in composition to the early solar nebula. A newly discovered comet might be on its first orbit of the Sun, and, as it heats and melts, the gases it emits can tell us about the chemical composition of the solar nebula.
DIF: Easy REF: Section 7.4
MSC: Understanding
OBJ: Describe how planetesimals become planets.
What are craters in the solar system evidence of?
ANS: Craters in the solar system are evidence of a time when the solar system had many small planetesimals that were colliding to form our present solar system.
DIF: Medium REF: Section 7.4
MSC: Remembering
OBJ: Describe how planetesimals become planets.
How did the formation of our Moon differ from the formation of the Galilean moons of Jupiter?
ANS: Astronomers believe that the formation of our Moon occurred due to a collision of a Mars-sized object with the early Earth. The remains of the planet eventually coalesced into our Moon. By contrast, the Galilean moons are believed to have formed naturally with the rest of the Solar System. Astronomers believe that the Jovian system formed its own mini accretion disk, out of which the Galilean moons formed around Jupiter, much as the planets formed around the Sun.
DIF: Medium REF: Section 7.4 MSC: Applying
OBJ: Describe how planetesimals become planets.
Approximately how massive are most of the extrasolar planets that have been discovered using the Doppler effect, and which planet in our Solar System is similar in mass? Why is the Doppler effect method more likely to find massive (rather than low-mass) planets and planets that are close to their stars?
ANS: The planets found are mostly smaller than Neptune, 2 to 10 times Earth’s mass. The Doppler effect is more likely to find massive planets because the Doppler shift of their parent star will be larger, because the gravitational pull is proportional to the mass. Also, it is easier to find a planet closer in because the force of gravity is stronger as it is inversely proportional to the square of the semimajor axis. Thus, more massive planets and planets closer to their star are easier to detect with the Doppler shift.
DIF: Easy REF: Section 7.5 MSC: Remembering
OBJ: Summarize the five methods that astronomers use to detect extrasolar planets.
Explain why most of the extrasolar planets that astronomers first detected were so-called “hot Jupiters.”
ANS: Originally technology did not allow us to detect smaller planets. The easiest planets to detect are massive planets, which cause their parent stars to wobble the most, in close orbits, which cause their parent stars to wobble faster.
DIF: Medium REF: Section 7.5 MSC: Applying
OBJ: Summarize the five methods that astronomers use to detect extrasolar planets.
Have any Earth-sized, terrestrial, extrasolar planets been detected? If so, explain what method(s) is(are) used.
ANS: The Kepler mission has been finding Earth-sized planets using the transit method to detect them and using the Doppler shift method to follow up and measure the radii, masses, and densities and to characterize them as either terrestrial or giant planets.
DIF: Medium REF: Section 7.5
MSC: Remembering
OBJ: Summarize the five methods that astronomers use to detect extrasolar planets.
In addition to the percentage reduction in light, is anything else needed to determine the size of the transiting planet?
ANS: The radius of the star is also needed to calculate the size of the transiting planet.
DIF: Medium REF: Section 7.5 MSC: Understanding
OBJ: Summarize the five methods that astronomers use to detect extrasolar planets.
Explain how astronomers use the Doppler effect to detect the presence of extrasolar planets.
ANS: As a planet orbits a star, the gravitational attraction between the planet and star causes them to orbit a common center of mass. To an outside observer, this causes the star to appear to “wobble.” As it does so, it periodically moves toward us and then away from us. These radial motions produce a Doppler effect in the spectra of the star. By measuring the Doppler effect, astronomers can infer the mass of the planet and its distance from the star.
DIF: Medium REF: Section 7.5 MSC: Applying
OBJ: Summarize the five methods that astronomers use to detect extrasolar planets.
What property of an extrasolar planet can be determined directly from the Doppler effect data shown in the figure below? What other properties of the planet can then be determined?
ANS: The period of repetition of the Doppler shifts is also the orbital period of the planet. The orbital distance and mass of the planet can then be calculated from the maximum orbital velocity observed along with Newton’s generalized version of Kepler’s third law, if the mass of the central star and the inclination of the orbit can be determined.
DIF: Medium REF: Section 7.5 MSC: Applying
OBJ: Summarize the five methods that astronomers use to detect extrasolar planets.
Briefly explain the five different observational methods we use to detect extrasolar planets. How many extrasolar planets have been discovered to date?
ANS: The five different observational methods we use to detect extrasolar planets are (1) using the Doppler shift to detect the motion of its parent star, (2) detecting transits when a planet moves in front of its parent star and dims it, (3) detecting microlensing events when the planet moves across the line of sight of its parent star and brightens it, (4) directly imaging the planet as it orbits its star, and (5) the astrometric method of precise measurement of a star’s position. Slightly more than 2000 extrasolar planets have been detected as of the writing of this textbook.
DIF: Medium REF: Section 7.5 MSC: Applying
OBJ: Summarize the five methods that astronomers use to detect extrasolar planets.
What evidence do we have that planetary systems are common in the universe?
ANS: Astronomers have directly observed disks around young stars. Astronomers have now detected more than 2000 planets.
DIF: Medium REF: Section 7.5
MSC: Remembering
OBJ: Summarize the five methods that astronomers use to detect extrasolar planets.
What is planet migration?
ANS: The force of gravity from all the nearby objects can move planets from the orbit they form in. This can cause planets to move inward or outward in the disk.
DIF: Medium REF: Section 7.5
MSC: Remembering
OBJ: Describe how planetary migration accounts for hot Jupiters being located very close to their host stars.
What are some limitations of the radial velocity method of exoplanet detection?
ANS: The star needs to be bright. Technological limitations prevent us from detecting Earth-massed planets. The star has to be moving toward or away from Earth; therefore, for a star system that is face-on (we see its pole directly) it is impossible to use this technique to detect a planet.
DIF: Medium REF: Section 7.5
MSC: Understanding
OBJ: Summarize the five methods that astronomers use to detect extrasolar planets.
What are some limitations of the transit method of exoplanet detection?
ANS: This method can only detect planets in systems that are aligned so that the plane of the star system is edge on, meaning the planet will pass in front of the star. The diameter of the planet relative to the star, needs to be large enough to cause a measurable decrease in the brightness of the star.
DIF: Medium REF: Section 7.5 MSC: Understanding
OBJ: Summarize the five methods that astronomers use to detect extrasolar planets.
Compare the orbital angular momentum of Earth and Jupiter. Which is larger and by how much? (Note that Jupiter’s mass is 318 times that of Earth, the semimajor axis of Jupiter’s orbit is 5.2 AU, and Jupiter’s orbital period is 12 years.)
ANS: The orbital angular momentum is equal to mvr, where m is the mass of the planet, v is its velocity, and r is the semimajor axis of its orbit. The velocity of a planet is v = 2πr/P, where P is the orbital period. Thus, the orbital angular momentum is proportional to mr2/P. Thus, the ratio of Jupiter’s angular momentum to Earth’s angular momentum is (MJ/ME) × (rJ/rE)2 × (PE/PJ) = 318 × 5.22/12 = 720.
DIF: Difficult REF: Working It Out 7.1 MSC: Applying
OBJ: Compute and compare orbital and spin angular momentum.
