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213 Cards in this Set
- Front
- Back
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How do we think the "hot Jupiters" around other stars were formed?
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They formed as gas giants beyond the frost line and then migrated inwards
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By itself, the Doppler technique provides a measure of a planet's
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all of the above
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Approximately how many other planetary systems have been discovered to date?
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a hundred
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Which of the following methods has led to the most discoveries of massive planets orbiting near their parent stars?
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detecting the gravitational effect of an orbiting planet by looking for the Doppler shifts in the star's spectrum
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Which of the following methods has not yet detected planets around other stars?
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detection of reflected light by the planet
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What are the two main differences between extrasolar planetary systems discovered to date and our Solar System?
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extrasolar planet orbits tend to be closer and more eccentric than in our Solar System
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Current techniques can measure stellar motion to less than
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walking speed
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Planets detected via the Doppler technique have been mostly
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Jupiter-mass, in very close orbits
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If every star had an Earth-like planet in an Earth-like orbit, how many could be detected by a transit?
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1 in 200
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Which planet search technique is currently best suited to finding Earth-like planets?
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transit
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What would happen to the planets in a solar system where the central star did not have a strong wind?
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The gas in the solar nebula would create a drag on the planets and their orbits would migrate inwards.
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The Doppler technique only provides a measure of the minimum mass of a planet because
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only the motion of star toward the observer is measured, not the full motion
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A planet's density can be measured by combining
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Doppler and transit observations
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Which of the following is not a planned space mission to search for extrasolar planets?
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Copernicus
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Why are many of the newly detected extrasolar planets called "hot Jupiters"?
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Their masses are similar to Jupiter but they are very close to the central star and therefore hot
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What observations are needed to tell whether an Earth-like planet is geologically alive or dead?
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images and spectra of the planet
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What is astrometry?
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measuring the positions of stars on the sky
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The composition of a planet can be determined by
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spectra
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The reason that most extrasolar planets are found close to their parent stars is
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the amount and frequency of the star's motion are both higher.
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What do models suggest make up the clouds on "hot Jupiters"?
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rock dust
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How much brighter is a Sun-like star than the reflected light from a planet orbiting around it?
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a billion times brighter
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A planet is detected via the Doppler technique. The repeating pattern of the stellar motion tells us
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the orbital period of the planet
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The first planets around other Sun-like stars were discovered
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about a decade ago.
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Which of the following is a consequence of the discovery of hot Jupiters for the nebular theory of solar system formation?
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It has been modified to allow for planets to migrate inwards or outwards due to gravitational interactions
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The astrometric technique of planet detection works best for
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massive planets around nearby stars
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A planet is detected via the Doppler technique. The shape of the periodic velocity pattern tells us
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the orbital eccentricity of the planet
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A planet is detected via the Doppler technique. The velocity change of the star is a measure of
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the planet's mass and orbital distance.
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The transit method of planet detection works best for
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big planets in edge-on orbits around around small stars
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The depth of the dip in a star's brightness due to the transit of a planet depends most directly on
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the planet's size.
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Viewed from afar, the transit of the Earth would cause the Sun's brightness to dim by approximately one part in
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10,000.
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The composition of a planet's atmosphere be measured during a transit by analyzing
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the excess absorption of starlight at specific wavelengths
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The size and shape of a planet's orbit can be determined by
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the Doppler technique
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Which of the following is a consequence of the discovery of hot Jupiters for understanding our own Solar System?
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It shows that we do not fully understand the formation of our Solar System.
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Most of the planets discovered around other stars
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are more massive than Earth and orbit very close to the star.
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Because we have not found another planetary system like our own, we can conclude that our Solar System must be quite unusual.
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False
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Most of the planets discovered around other stars are more massive than Jupiter.
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True
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The Doppler technique for planet detection has found Earth like planets around nearby Sun-like stars
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False
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Astronomers have discovered more planets around other stars than in our Solar System
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True
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The density of a planet can be determined by combining Doppler and astrometric measurements.
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False
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Why are neutrinos so difficult to detect?
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because they rarely interact with matter
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Which is the strongest of the fundamental forces in the universe?
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strong force
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Which of the following statements about neutrinos is not true?
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The mass of a neutrino is 30 percent of the mass of an electron.
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Based on its surface temperature of 5,800 K, what color are most of the photons that leave the Sun's surface?
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green
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Why do sunspots appear dark in pictures of the Sun?
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They actually are fairly bright but appear dark against the even brighter background of the surrounding Sun.
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What is the Sun made of?
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70 percent hydrogen, 28 percent helium, 2 percent other elements
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Most of the energy produced in the Sun is released in the form of visible light from the photosphere. However, some energy is released from the upper layers of the solar atmosphere. Which of the following best describes where other forms of light are released?
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The chromosphere is the source of ultraviolet light, and the corona is the source of X rays.
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What happens to energy in the convection zone of the Sun?
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Energy is transported outward by the rising of hot plasma and the sinking of cooler plasma.
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What are coronal holes?
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areas of the corona where magnetic field lines project into space, allowing charged particles to escape the Sun, becoming the solar wind
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In the late 1800s, Kelvin and Helmholtz suggested that the Sun stayed hot thanks to gravitational contraction. What was the major drawback of this idea?
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It predicted that the Sun could last only about 25 million years, which is far less than the age of the earth.
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The core of the Sun is
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hotter and denser than the surface
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What processes are involved in the sunspot cycle?
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the winding of magnetic field lines due to differential rotation
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Suppose that, for some unknown reason, the core of the Sun suddenly became hotter. Which of the following best describes what would happen?
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Higher temperature would cause the rate of nuclear fusion to rise, which would increase the internal pressure, causing the core to expand and cool until the fusion rate returned to normal.
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From the center outward, which of the following lists the "layers" of the Sun in the correct order?
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core, radiation zone, convection zone, photosphere, chromosphere, corona
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The phase of matter in the Sun is
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plasma
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Hydrogen fusion in the Sun requires a temperature (in Kelvin) of
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millions of degrees
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How do human-built nuclear power plants on Earth generate energy?
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nuclear fission
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The light radiated from the Sun's surface reaches Earth in about 8 minutes, but the energy of that light was released by fusion in the solar core about
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a million years ago.
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Suppose you put two protons near each other. Because of the electromagnetic force, the two protons will
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repel each other
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What two forces are balanced in what we call gravitational equilibrium?
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outward pressure and gravity
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How does the Sun generate energy today?
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nuclear fusion
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The first step in the proton-proton chain produces an antielectron, or positron. What happens to the positron?
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It is rapidly converted to energy when it meets an ordinary electron, resulting in matter-antimatter annihilation
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What are the appropriate units for the Sun's luminosity?
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watts
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Which is closest to the temperature of the core of the Sun?
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10 million K
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What is granulation in the Sun?
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the bubbling pattern on the photosphere produced by the underlying convection
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What is a possible solution to the solar neutrino problem?
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The electron neutrinos created in the Sun change into another type of neutrino that we do not detect
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How much mass does the Sun lose through nuclear fusion per second?
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4 million tons
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Studies of sunquakes, or helioseismology, have revealed that
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our mathematical models of the solar interior are fairly accurate.
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What observations characterize solar maximum?
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We see many sunspots on the surface of the Sun.
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What is the average temperature of the surface of the Sun?
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6,000 K
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What do we mean when we say that the Sun is in gravitational equilibrium?
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There is a balance within the Sun between the outward push of pressure and the inward pull of gravity.
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Which of the following statements about the sunspot cycle is not true?
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The rate of nuclear fusion in the Sun peaks about every 11 years.
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Which layer of the Sun do we normally see?
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photosphere
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Sunspots are cooler than the surrounding region of the Sun's surface.
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True
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Energy from the core of the Sun first travels slowly through the convection zone and then much faster through the radiation zone.
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False
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The Sun is a relatively young star, near the beginning of its life.
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False
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The Sun generates energy primarily by nuclear fission
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False
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The proton-proton chain converts four hydrogen nuclei into one helium nucleus.
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True
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The core of the Sun is at a temperature of about 20,000 K.
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False
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The corona and chromosphere are hotter than the photosphere.
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True
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Although the Sun does not generate energy by gravitational contraction today, this energy-generation mechanism was important when the Sun was forming.
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True
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The chromosphere is the layer of the Sun that we see as its visible surface.
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False
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Gravitational equilibrium means that the surface and the core of the Sun are at the same pressure.
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False
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The spectral sequence in order of decreasing temperature is
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OBAFGKM
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Which of the following persons reorganized the spectral classification scheme into the one we use today and personally classified over 400,000 stars?
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Annie Jump Cannon
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Approximately, what basic composition are all stars born with?
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three-quarters hydrogen, one-quarter helium, no more than 2 percent heavier elements
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On a Hertzsprung-Russell diagram, where would we find white dwarfs?
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lower left
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Which of the following correctly states the luminosity-distance formula?
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apparent brightness
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On a Hertzsprung-Russell diagram, where would we find stars that have the largest radii?
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upper right
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Why do astronomers often measure the visible-light apparent brightness instead of the total apparent brightness of a star?
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In order to measure the total apparent brightness of a star, you must measure its brightness in all wavelengths, and this is difficult to do. The only wavelengths you can measure from the surface of the earth are visible and radio wavelengths.
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The most distant stars we can measure stellar parallax for are approximately
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100 parsecs away.
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On a Hertzsprung-Russell diagram, where on the main sequence would we find stars that have the greatest mass?
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upper left
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Which of the following statements about an open cluster is true?
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All stars in the cluster are approximately the same age
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What are the standard units for luminosity?
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watts
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A star of spectral type G lives approximately how long on the main sequence?
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10 billion years
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Suppose you measure the parallax angle for a particular star to be 0.1 arcsecond. The distance to this star is
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10 parsecs.
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Which of the following best describes the axes of a Hertzsprung-Russell (H-R) diagram?
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surface temperature on the horizontal axis and luminosity on the vertical axis
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You observe a star in the disk of the Milky Way, and you want to plot the star on an H-R diagram. You will need to determine all of the following, except the
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rotation rate of the star.
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A star's luminosity is the
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total amount of light that the star radiates each second.
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Which of the following persons used the ideas of quantum mechanics to describe why the spectral classification scheme is in order of decreasing temperature?
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Cecilia Payne-Gaposchkin
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On a Hertzsprung-Russell diagram, where would we find red giant stars?
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upper right
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In a pulsating variable star, which characteristic of the star changes dramatically with time?
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luminosity
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Since all stars begin their lives with the same basic composition, what characteristic most determines how they will differ?
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mass they are formed with
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Which of the following terms is given to a pair of stars that we can determine are orbiting each other only by measuring their periodic Doppler shifts?
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spectroscopic binary
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Which of the following luminosity classes refers to stars on the main sequence?
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V
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The spectral sequence sorts stars according to
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surface temperature
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On the main sequence, stars obtain their energy
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by converting hydrogen to helium
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If the distance between us and a star is doubled, with everything else remaining the same, the luminosity
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remains the same, but the apparent brightness is decreased by a factor of four.
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Which of the following statements about a globular cluster is true?
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Most stars in the cluster are yellow or reddish in color.
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On a Hertzsprung-Russell diagram, where would we find stars that are cool and dim?
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lower right
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Which of the following is the most common type of main-sequence star?
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an M star
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Which of the following terms is given to a pair of stars that appear to change positions in the sky, indicating that they are orbiting one another?
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visual binary
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Why are Cepheid variables so important for measuring distances in astronomy?
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Their luminosity can be inferred from their period.
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A star of spectral type O lives approximately how long on the main sequence?
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1 million years
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Which of the following characteristics of stars has the greatest range in values?
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luminosity
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Suppose that you measure the parallax angle for a particular star to be 0.5 arcsecond. The distance to this star is
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2 parsecs.
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On a Hertzsprung-Russell diagram, where would we find stars that are cool and luminous?
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upper right
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Which of the following statements about apparent and absolute magnitudes is true?
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All of the above are true.
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Cluster ages can be determined from
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main sequence turnoff
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The faintest star visible to the naked eye has an apparent visual magnitude of about
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6.
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Which of the following is true about low-mass stars compared to high-mass stars?
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Low-mass stars are cooler and less luminous than high-mass stars.
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Suppose you see two main-sequence stars of the same spectral type. Star 1 is dimmer in apparent brightness than Star 2 by a factor of 100. What can you conclude? (Neglect any effects that might be caused by interstellar dust and gas.)
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Star 1 is 10 times more distant than Star 2.
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Which of the following statements about spectral types of stars is true?
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All of the above are true
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Why is the spectral sequence of stars not alphabetical?
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The original alphabetical labeling did not correspond to surface temperature and thus had to be reordered.
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All stars spend approximately the same amount of time on the main sequence
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False
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Two stars have the same spectral type. Star X is in luminosity class III, while Star Y is in luminosity class V. Therefore, Star X is larger in radius than Star Y.
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True
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We can measure the radii of stars in an eclipsing binary system, in addition to the masses
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True
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The more distant a star, the smaller its parallax.
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True
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A 10 solar mass star is about ten times more luminous than a 1 solar mass star
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False
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The apparent brightness of a star depends only on its luminosity.
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False
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We can measure stellar parallax for most stars in our galaxy.
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False
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Some stars are cool enough to have molecules in their atmosphere.
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True
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What is the likely reason that we cannot find any examples of the first generation stars?
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The first generation stars were all very massive and exploded as supernova.
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What happens to the rotation of a molecular cloud as it collapses to form a star?
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The rotation rate increases and results in a disk of material around a protostar
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Calculations show that gravity begins to overcome thermal pressure in clouds that are
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massive than a hundred times the Sun.
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What happens to the visible radiation produced by new stars within a molecular cloud?
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It is absorbed by dust grains and heats up the cloud
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The thermal pressure of a gas depends on
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density and temperature
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What is the greatest mass a newborn star can have
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100 solar masses.
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If you wanted to observe a molecular cloud, in what wavelength of light would you most likely observe?
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infrared
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The typical density and temperature of molecular clouds are
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300 molecules per cubic centimeter, 10-30 Kelvin.
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Astronomers estimate that new stars from in our galaxy at the rate of about
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a few (2-3) per year.
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What is the range of timescales for star formation?
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from 1 million years for the most massive stars up to 100 million years for the least massive stars
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What happens to the surface temperature and luminosity when a protostar undergoes convective contraction?
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Its surface temperature remains the same and its luminosity decreases
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The most abundant molecule in molecular clouds is
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H2
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The typical size of an interstellar dust grain is
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1 micrometer.
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What is the eventual fate of a brown dwarf?
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It gradually cools down and becomes ever dimmer.
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When is thermal energy trapped in the dense center of a cloud?
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when excited molecules collide with other molecules before they can release a photon
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By mass, the interstellar medium in our region of the Milky Way consists of
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70% Hydrogen, 28% Helium, 2% heavier elements
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What is the minimum temperature for a cloud to excite emission lines from H2?
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100 K
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What percentage of a molecular cloud's mass is interstellar dust?
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1%
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How do astronomers infer the presence of magnetic fields in molecular clouds?
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by measuring the polarization of starlight passing through the cloud
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Why do we think the first generation of stars would be different from stars born today?
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Without heavy elements, the clouds could not reach as low a temperature as today and had to be more massive to collapse.
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Where would a brown dwarf be located on an H-R diagram?
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below and to the right of the lowest part of the main sequence
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What is the difference between brown dwarfs and Jupiter?
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Brown dwarfs are more massive than Jupiter
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What property of a molecular cloud does not counteract gravitational contraction?
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fragmentation
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What are the letters that follow the spectral sequence OBAFGKM?
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LT
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What prevents a brown dwarf from undergoing nuclear fusion?
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Degeneracy pressure halts the contraction of a protostar so the core never becomes hot or dense enough for nuclear fusion.
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When does a star become a main-sequence star?
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when the rate of hydrogen fusion within the star's core is high enough to maintain gravitational equilibrium
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The gravitational force in a molecular cloud depends on
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density only
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What happens to the surface temperature and luminosity when gravity first assembles a protostar from a collapsing cloud?
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Its surface temperature and luminosity increase
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When does a protostar become a true star?
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when nuclear fusion begins in the core
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The most common constituent of molecular clouds, H2, is rarely detected within them
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True
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Most stars are born in clusters containing thousands of stars
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True
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Although some photographs show what looks like jets of material near many young stars, we now know that these "jets" actually represent gas from the surrounding nebula that is falling onto the stars
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False
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Clouds that appear dark in visible light often glow when observed at long infrared wavelengths
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True
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No stars have been found composed solely of Hydrogen and Helium (and no heavier elements)
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True
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Protostars start off more luminous than the main sequence stars they become
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True
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In any star cluster, stars with lower masses greatly outnumber those with higher masses
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True
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There is no limit to the mass with which a star can be born.
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False
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Molecular clouds appear more transparent at longer wavelengths
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True
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There is no limit to the mass with which a star can be born
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False
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Molecular clouds appear more transparent at longer wavelengths
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True
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Photographs of many young stars show long jets of material apparently being ejected from their poles.
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True
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The helium fusion process results in the production of
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carbon
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Which of the following properties make flare stars so active?
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both A and B
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At approximately what temperature can helium fusion occur?
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100 million K
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What is a carbon star?
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a red giant star whose atmosphere becomes carbon-rich through convection from the core
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Which of the following statements about stages of nuclear burning (i.e., first-stage hydrogen burning, second-stage helium burning, etc.) in a massive star is not true?
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Each successive stage lasts for approximately the same amount of time
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Which stars have convective cores?
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high-mass stars
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Most interstellar dust grains are produced in
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the atmospheres of red giant stars
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The following questions refer to the H-R diagram below that shows the life track of a 1-solar-mass star, with various stages labeled with Roman numerals
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viii
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Which two energy sources can help a star maintain its internal thermal pressure?
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nuclear fusion and gravitational contraction
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Compared to the star it evolved from, a red giant is
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cooler and brighter.
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What is happening inside a star while it expands into a subgiant?
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It is fusing hydrogen into helium in a shell outside the core.
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The following questions refer to the sketch below of an H-R diagram for a star cluster.
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by hydrogen shell burning around an inert helium core
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What happens to the core of a star after a planetary nebula occurs?
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It becomes a white dwarf
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Compared to the star it evolved from, a white dwarf is
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hotter and dimmer
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Suppose the star Betelgeuse (the upper left shoulder of Orion) were to become a supernova tomorrow (as seen here on Earth). What would it look like to the naked eye?
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Betelgeuse would remain a dot of light but would suddenly become so bright that, for a few weeks, we'd be able to see this dot in the daytime
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You discover a binary star system in which one member is a15MSun main-sequence star and the other star is a 10MSun giant. How do we believe that a star system such as this might have come to exist?
|
The giant must once have been the more massive star but transferred some of its mass to its companion
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You discover a binary star system in which one member is a 15MSun main-sequence star and the other star is a 10MSun giant. Why should you be surprised, at least at first?
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The two stars should be the same age, so the more massive one should have become a giant first
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What can we learn about a star from a life track on an H-R diagram?
|
what surface temperature and luminosity it will have at each stage of its life
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Why is Supernova 1987A particularly important to astronomers?
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It was the nearest supernova detected in nearly 400 years
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What happens when a star exhausts its core hydrogen supply?
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Its core contracts, but its outer layers expand and the star becomes bigger and brighter
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Why does a star grow larger after it exhausts its core hydrogen?
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Hydrogen fusion in a shell outside the core generates enough thermal pressure to push the upper layers outward
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All of the following are involved in carrying energy outward from a star's core except
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conduction
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Which element has the lowest mass per nuclear particle and therefore cannot release energy by either fusion or fission?
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iron
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What type of star is our Sun?
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low-mass star
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Which event marks the beginning of a supernova?
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the sudden collapse of an iron core into a compact ball of neutrons
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Which of the following statements about degeneracy pressure is not true?
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Degeneracy pressure varies with the temperature of the star
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What is a planetary nebula?
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the expanding shell of gas that is no longer gravitationally held to the remnant of a low-mass star
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What happens when the gravity of a massive star is able to overcome neutron degeneracy pressure?
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The core contracts and becomes a black hole.
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What do astronomers mean when they say that we are all "star stuff"?
|
that the carbon, oxygen, and many elements essential to life were created by nucleosynthesis in stellar cores
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What types of stars end their lives with supernovae?
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stars that are at least several times the mass of the Sun
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What happens after a helium flash?
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The core quickly heats up and expands
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How many helium nuclei fuse together when making carbon?
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3
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What is the CNO cycle?
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a type of hydrogen fusion that uses carbon, nitrogen, and oxygen atoms as catalysts
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After a supernova event, what is left behind?
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either a neutron star or a black hole
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What is the range of star masses for high-mass stars?
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between 8 and 100 solar masses
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Which of the following spectral types is more likely to be a flare star?
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MV
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There is no limit to the mass with which a star can be born
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False
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In any star cluster, stars with lower masses greatly outnumber those with higher masses.
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True
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Stars with high masses live longer than stars with lower masses
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False
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All stars that become supernovae will leave behind a neutron star
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False
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The helium fusion process works by fusing two helium nuclei into one beryllium nucleus
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False
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