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103 Cards in this Set
- Front
- Back
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From the fact that virtually every galaxy is moving away from us and more distant galaxies are moving away from us at a faster rate than closer ones, we conclude that
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the universe is expanding.
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How many galaxies are there in the observable universe?
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roughly (within a factor of 10) the same as the number of stars in our galaxy
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Which of the following is smallest?
-1 light-second - size of a typical star - size of a typical planet - 1 AU |
size of a typical planet
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What is nuclear fusion?
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the process of combining lightweight nuclei to make heavier nuclei
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By studying distant galaxies in the 1920s, Hubble made the following important discovery that led us to conclude that the universe is expanding:
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All galaxies outside the Local Group are moving away from us, and the farther away they are, the faster they're going.
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If we use 1 millimeter to represent 1 light-year, how large in diameter is the Milky Way Galaxy?
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100 meters
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On the scale of the cosmic calendar, in which the history of the universe is compressed to 1 year, how long has human civilization (i.e., since ancient Egypt) existed?
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a few seconds
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Based on observations of the universal expansion, the age of the universe is about
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14 billion years.
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What do we mean when we say that the universe is expanding?
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Average distances between galaxies are increasing.
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An example in which you are traveling at constant speed but not at constant velocity?
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driving around in a circle at exactly 100 km/hr
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Best describe what we mean by the universe?
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the sum total of all matter and energy
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If we imagine the history of the universe compressed into one year, the first dinosaurs became extinct
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yesterday.
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How long would it take to count all the stars in the Milky Way Galaxy at a rate of one star per second?
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several thousand years
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Using the ideas discussed in the text, in what sense are we "star stuff"?
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Nearly every atom from which we are made was once inside of a star.
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How are galaxies important to our existence?
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Galaxies recycle material from one generation of stars to the next, and without this recycling we could not exist.
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How many arcseconds are in 1°?
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3,600
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What effect or effects would be most significant if the Moon's orbital plane were exactly the same as the ecliptic plane?
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Solar eclipses would be much more frequent
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Is the following statements about the Moon true?
The Moon's distance from Earth varies during its orbit. |
Yes its True
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If the Moon rises around 3 A.M., its phase must be
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waning crescent.
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By locating the north celestial pole (NCP) in the sky, how can you determine your latitude?
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The altitude of the NCP is the same as your latitude.
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Orion is visible on winter evenings but not summer evenings because of
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the location of Earth in its orbit.
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The precession of the Moon's nodes means that
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the eclipse seasons occur less than 6 months apart.
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We describe a location on Earth's surface by stating its
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latitude and longitude.
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What is the saros cycle?
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the roughly 18-year cycle over which the pattern of eclipses repeats
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statement that does not use the term angular size or angular distance correctly?
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The angular distance between those two bright stars in the sky is about 2 meters.
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Use the term angular size or angular distance correctly.
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-The angular distance between those two houses in the distance is 30 degrees.
-The angular size of the Sun is about the same as that of the Moon. -You can use your outstretched hand against the sky to estimate angular sizes and angular distances. |
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About how many stars are visible to the naked eye on a clear, dark night away from city lights?
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a couple thousand
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An angle of 1 arcsecond is
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about the width of a finger held at arm's length.
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Suppose it is full moon. What phase of Earth would someone on the Moon see at this time?
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new Earth
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If our year were twice as long (that is, if Earth took twice as many days to complete each orbit around the Sun), but Earth's rotation period and axis tilt were unchanged, then
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the four seasons would each be twice as long as they are now.
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Suppose you see a photo showing Jupiter half in sunlight and half in shadow (that is, a first quarter Jupiter). This photo might have been taken by
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the Galileo spacecraft, when it was orbiting Jupiter.
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What is meant by a scientific paradigm?
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a generally well established scientific theory or set of theories
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When did Ptolemy live?
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about 2000 years ago
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He discovered that the orbits of planets are ellipses.
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Kepler
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The following statement about scientific theories is not true. Why?
A theory cannot be taken seriously by scientists if it contradicts other theories developed by scientists over the past several hundred years. |
Anytime we discover new "facts," we must be prepared to revise or discard old theories that cannot explain them. However, the new theory must still explain all the old "facts" discovered previously. Thus, for example, Einstein's theory of relativity provided a new view of gravity, but it still explains all the facts that previously were explained in the context of Newton's law of gravity. Newton's law remains a viable way of explaining the old facts, although we no longer consider it to be the best theory of gravity.
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Why did Ptolemy have the planets orbiting Earth on "circles upon circles" in his model of the universe?
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to explain the fact that planets sometimes appear to move westward, rather than eastward, relative to the stars in our sky
The circles upon circles explained retrograde motion, but a much simpler explanation is that Earth is a planet going around the Sun and we see retrograde motion as we pass by another planet in its orbit. |
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The Metonic cycle is the
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19-year period over which the lunar phases occur on about the same dates.
Because 19 years is almost precisely equal to 235 lunar months. |
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The first to prove that comets lie beyond Earth's atmosphere.
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Tycho Brahe
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Ptolemy was important in the history of astronomy because he
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developed a model of the solar system that made sufficiently accurate predictions of planetary positions to remain in use for many centuries.
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The names of the seven days of the week are based on
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the seven naked-eye objects that appear to move among the constellations.
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Scientific models are used to
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make specific predictions that can be tested through observations or experiments.
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In science, a broad idea that has been repeatedly verified so as to give scientists great confidence that it represents reality is called
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a theory.
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Best describe how modern astronomers view astrology?
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Astrology played an important part in the development of astronomy in ancient times, but it is not a science by modern standards.
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How does a 12-month lunar calendar differ from our 12-month solar calendar?
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It has a bout 11 fewer days.
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Galileo observed all of the following. Which observation offered direct proof of a planet orbiting the Sun?
- patterns of shadow and sunlight near the dividing line between the light and dark portions of the Moon's face. - the Milky Way is composed of many individual stars. - four moons orbiting Jupiter. - phases of Venus. |
phases of Venus.
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According to Kepler's third law (p2 = a3), how does a planet's mass affect its orbit around the Sun?
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A planet's mass has no effect on its orbit around the Sun.
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According to what we now know from Newton's laws, what best explains why Kepler's second law is true?
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A planet's total orbital energy must be conserved as it moves around its orbit.
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Changing the orbit of a spacecraft by firing thrusters is an example of
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Newton's third law of motion.
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According to the universal law of gravitation, the force due to gravity is
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inversely proportional to the square of the distance between objects.
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You are standing on a scale in an elevator. Suddenly you notice your weight decreases. What do you conclude?
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The elevator is accelerating downwards.
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The ultimate source of energy that powers the Sun is
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mass energy of hydrogen fusing into helium.
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What would happen if the Space Shuttle were launched with a speed greater than Earth's escape velocity?
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It would travel away from Earth into the solar system.
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Suppose an object is moving in a straight line at 50 mi/hr. According to Newton's first law of motion, the object will
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continue to move in the same way until it is acted upon by a force.
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What does temperature measure?
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the average kinetic energy of particles in a substance
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Approximately where is it currently high tide on Earth?
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on the portion of Earth facing directly toward the Moon and on the portion of Earth facing directly away from the Moon
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Momentum is defined as
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mass times velocity.
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In what case would you feel weightless?
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while falling from a roof
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When a rock is held above the ground, we say it has some potential energy. When we let it go, it falls and we say the potential energy is converted to kinetic energy. Finally, the rock hits the ground (and stays there). What has happened to the energy?
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The energy goes to producing sound and to heating the ground, rock and surrounding air.
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Best describe the origin of ocean tides on Earth?
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Tides are caused by the difference in the force of gravity exerted by the Moon across the sphere of Earth.
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Suppose you heat up an oven to 400 degrees F and boil a pot of water. Explain why you would be burned by sticking your hand briefly in the pot but not by sticking your hand briefly in the oven?
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The water can transfer heat to your arm more quickly than the air.
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Suppose that a lone asteroid happens to be passing Jupiter on an unbound orbit that keeps it well above Jupiter's atmosphere and far from all of Jupiter's moons. What statement would be true?
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The asteroid's orbit around Jupiter would not change, and it would go out on the same unbound orbit that it came in on.
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Not a good reason to place observatories on remote mountain tops?
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to be able to observe at radio wavelengths
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Good reasons to place observatories on remote mountain tops?
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- to reduce light pollution
- to reduce light distortion - to reduce light absorption |
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Which of the following objects is not a close approximation of a thermal emitter?
- you - a planet - a star - hot, thin gas - a filament in a light bulb |
hot, thin gas
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An electron-volt is
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an amount of energy much smaller than a joule.
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If you heat a gas so that collisions are continually bumping electrons to higher energy levels, when the electrons fall back to lower energy levels the gas produces
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an emission line spectrum.
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How are wavelength, frequency, and energy related for photons of light?
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Longer wavelength means lower frequency and lower energy.
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Currently, the largest optical telescope mirrors have a diameter of
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10 Meters.
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A gas heated to millions of degrees would emit
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mostly X rays.
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The stars in our sky twinkle in brightness and color because of
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turbulence in Earth's atmosphere.
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An atom that has fewer electrons than protons is called a/an
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ion.
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If we say that a material is opaque to ultraviolet light, we mean that it
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absorbs ultraviolet light.
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From shortest to longest wavelength, which of the following correctly orders the different categories of electromagnetic radiation?
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gamma rays, X rays, ultraviolet, visible light, infrared, radio
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From laboratory measurements, we know that a particular spectral line formed by hydrogen appears at a wavelength of 486.1 nanometers (nm). The spectrum of a particular star shows the same hydrogen line appearing at a wavelength of 486.0 nm. What can we conclude?
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The star is moving toward us.
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Which of the following best describes why we say that light is an electromagnetic wave?
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The passage of a light wave can cause electrically charged particles to move up and down.
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Not an advantage of the Hubble Space Telescope over ground-based telescopes?
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It is closer to the stars.
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Advantage of the Hubble Space Telescope over ground-based telescopes?
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- It can observe infrared and ultraviolet light, as well as visible light.
- It never has to close because of cloudy skies. - Stars do not twinkle when observed from space. |
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According to the universal law of gravitation, if you double the masses of both attracting objects, then the gravitational force between them will
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increase by a factor of 4.
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What quantities does angular momentum depend upon?
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mass, velocity, and radius
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Gasoline is useful in cars because it has
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chemical potential energy.
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As long as an object is not gaining or losing mass, a net force on the object will cause a change in
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velocity.
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Absolute zero is
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0° Kelvin.
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What do we mean by the orbital energy of an orbiting object (such as a planet, moon, or satellite)?
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Orbital energy is the sum of the object's kinetic energy and its gravitational potential energy as it moves through its orbit.
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What is the difference between a bound orbit and an unbound orbit around the Sun?
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An object on a bound orbit follows the same path around the Sun over and over, while an object on an unbound orbit approaches the Sun just once and then never returns.
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Suppose the Sun shrank in size but its mass remained the same. What would happen to the orbit of Earth?
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Earth's orbit would be unaffected.
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Suppose you are in an elevator that is traveling upward at constant speed. How does your weight compare to your normal weight on the ground?
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It is the same.
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Pair of facts that can be used with Newton's version of Kepler's third law to determine the mass of the Sun?
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Earth is 150 million km from the Sun and orbits the Sun in one year.
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What is not an exception to the general patterns of motion in the solar system?
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the rings of Saturn
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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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How does the Sun's mass compare with that of the planets?
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It is a thousand times more massive than all the planets combined.
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Where are most of the known asteroids found?
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between the orbits of Mars and Jupiter
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What percentage of the mass of the solar nebula consisted of elements other than hydrogen and helium?
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2 percent
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According to our theory of solar system formation, why do we find some exceptions to the general rules and patterns of the planets?
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Most of the exceptions are the result of giant impacts or close gravitational encounters.
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Why did the solar nebula heat up as it collapsed?
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As the cloud shrank, its gravitational potential energy was converted to thermal energy.
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In essence, the nebular theory holds that
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our solar system formed from the collapse of an interstellar cloud of gas and dust.
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List the eight major planets of our solar system in the correct order from closest to farthest from the Sun?
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Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
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Best describe how we have discovered nearly all of the more than 100 extrasolar planets known to date?
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We have not seen the planets directly, but rather have seen slight motions of stars that we attribute to the gravitational influence of orbiting planets.
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Statement about Mars that is not true.
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We could survive on Mars without spacesuits, as long as we brought oxygen in scuba tanks.
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True statements about Mars.
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- It is frozen today, but once had flowing water.
- It is considered part of our inner solar system. - We have landed spacecraft on its surface. |
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In what way is Venus most similar to Earth?
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both planets are nearly the same size.
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New idea that has been added into our theory of solar system formation as a result of the discoveries of extrasolar planets?
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Jovian planets can migrate from the orbits in which they are born.
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How is Einstein's famous equation, E = mc2, important in understanding the Sun?
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It explains the fact that the Sun generates energy by losing some 4 million tons of mass each day.
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According to our basic scenario of solar system formation, why do the jovian planets have numerous large moons?
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As the growing jovian planets captured gas from the solar nebula, the gas formed swirling disks around them, and moons formed from condensation accretion within these disks.
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