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# Astronomy A Beginners Guide to the Universe 7th Edition Test Bank

Astronomy: A Beginner’s Guide to the Universe, 7e (Chaisson/McMillan)
Chapter 1 The Copernican Revolution: The Birth of Modern Science

1) According to Newton’s third law, when the Voyager probes passed Jupiter in 1979, they exerted exactly the same force on Jupiter as the giant planet did on them.
Diff: 3
Section Ref.: 1.4

2) Compared to when it was on the surface, a satellite in an orbit whose radius is about 4 times the Earth’s radius will experience about 1/16 the force due to the Earth’s gravity.
Diff: 3
Section Ref.: 1.4

3) According to Newton’s second law, if you double the force acting on a body, the acceleration will double.
Diff: 2
Section Ref.: 1.4

4) According to Newton’s first law, an object traveling in a circle does not have a force acting on it.
Diff: 1
Section Ref.: 1.4

5) Kepler’s third law allows us to find the average distance to a planet from observing its period of rotation on its axis.
Diff: 2
Section Ref.: 1.3

6) According to Kepler’s third law, if you know the planet’s orbital period, you can find its average distance from the Sun.
Diff: 2
Section Ref.: 1.3

7) A planet (or comet) will speed up as it approaches the Sun.
Diff: 2
Section Ref.: 1.3
8) Kepler found the orbits of planets are ellipses, not circles.
Diff: 1
Section Ref.: 1.3
9) Kepler relied heavily on the telescopic observations of Galileo in developing his laws of planetary motion.
Diff: 2
Section Ref.: 1.3

10) Kepler’s third law relates the square of the planet’s orbital period in years to the cube of its average distance from the Sun in astronomical units.
Diff: 1
Section Ref.: 1.3

11) Among Galileo’s discoveries with his telescope were sunspots.
Diff: 1
Section Ref.: 1.2

12) Galileo’s observations of the entire phase cycle of Venus proved that Ptolemy’s epicycles could not be correct in keeping Venus between us and the Sun.
Diff: 1
Section Ref.: 1.2

13) According to Copernicus, retrograde motion occurs at opposition for the outer planets.
Diff: 2
Section Ref.: 1.1

14) In Ptolemy’s geocentric model, the planet’s motion along its deferent is all that is needed to understand retrograde motion.
Diff: 1
Section Ref.: 1.1

15) Copernicus believed the Earth was the center of all celestial motion.
Diff: 1
Section Ref.: 1.1
16) In Ptolemy’s geocentric model, retrograde motion occurs when the planet is closest to us, on the inside portion of the
A) deferent.
B) ellipse.
C) epicycle.
D) equant.
E) ecliptic.
Diff: 1
Section Ref.: 1.1
17) In Ptolemy’s geocentric model, the normal eastward motion of the planets was along
A) a deferent.
B) an epicycle.
D) an ellipse.
E) the equant.
Diff: 1
Section Ref.: 1.1

18) Copernicus’ Heliocentric theory explains that
A) planetary orbits are elliptical in shape.
B) the Sun lies at one focus of an ellipse.
C) Venus retrogrades when she overtakes us at inferior conjunction.
D) all planets lie between the Sun and Earth.
E) Mars will retrograde when it reaches a certain position on its epicycle.
Diff: 2
Section Ref.: 1.1

19) According to Copernicus, retrograde motion for Venus must occur around
A) inferior conjunction, when it passes between us and the Sun.
B) quadrature, when the planet is 90 degrees away from the Sun.
C) greatest elongation, when the planet is farthest from the Sun.
D) superior conjunction, when the planet is on the far side of the Sun.
E) opposition, when the planet lies opposite the Sun in the sky.
Diff: 2
Section Ref.: 1.1
20) According to Copernicus, the retrograde motion for Mars must occur
A) at inferior conjunction, when Mars laps the Earth and passes between us and the Sun.
B) at superior conjunction, when Mars lies on the far side of the Sun.
C) at quadrature, when Mars lies exactly 90 degrees east or west of the Sun.
D) at greatest elongation, when Mars can get up to 47 degrees from the Sun.
E) at opposition, when the Earth overtakes Mars and passes between Mars and the Sun.
Diff: 2
Section Ref.: 1.1

21) A fatal flaw with Ptolemy’s model is its inability to predict the observed phases of
A) the Sun during an eclipse.
B) the Moon in its monthly cycle.
C) Mercury and Venus.
D) Mars and Jupiter.
E) Jupiter and Saturn.
Diff: 2
Section Ref.: 1.2
22) Which of these was NOT seen telescopically by Galileo?
A) sunspots
B) Venus’ phase cycle
C) Four moons around Jupiter
D) stellar parallax
E) craters and mare on the Moon
Diff: 1
Section Ref.: 1.2

23) Which of these observations of Galileo refuted Ptolemy’s epicycles?
A) the complete cycle of Venus’ phases
B) the rotation of sunspots across the Sun’s surface
C) the revolution of Jupiter’s moons around it
D) the craters on the Moon
E) the visibility of many more stars with the telescope
Diff: 2
Section Ref.: 1.2
24) Galileo found the rotation period of the Sun was approximately
A) a day.
B) a week.
C) a month.
D) three months.
E) a year.
Diff: 3
Section Ref.: 1.2

25) Tycho Brahe’s contribution to Kepler’s Laws of Planetary Motion were
A) his detailed and accurate observations of the planets’ positions.
B) his observations of Jupiter’s moons.
C) a mathematical explanation of epicycles.
D) a precise lunar calendar.
E) the correct explanation of lunar phases.
Diff: 1
Section Ref.: 1.3

26) Kepler’s first law worked, where Copernicus’ original heliocentric model failed, because Kepler described the orbits as
A) elliptical, not circular.
B) much larger than Copernicus had envisioned.
C) around the Sun, not the Earth.
D) being on equants instead of epicycles.
E) complex, with epicycles to account for retrograde motions.
Diff: 1
Section Ref.: 1.3
27) When a planet’s orbit takes it closest to the Sun, it’s called
A) vernal equinox.
B) aphelion.
C) perihelion.
D) crossing the ecliptic.
E) none of these; a planet’s distance from the Sun never changes.
Diff: 2
Section Ref.: 1.3
28) A planet whose distance from the Sun is 3 AU would have an orbital period of how many Earth-years?
A) 3
B)
C)
D) 9
E) 81
Diff: 3
Section Ref.: 1.3

29) The force of gravity varies with the
A) product of the two masses.
B) inverse of the distance separating the two bodies.
C) inverse square of the distance separating the two bodies.
D) Both A and B are correct.
E) Both A and C are correct.
Diff: 1
Section Ref.: 1.4

30) A circular orbit would have an eccentricity of
A) 0.
B) between 0 and 0.5.
C) between 0.5 and 1.
D) exactly 1.0.
E) infinity.
Diff: 1
Section Ref.: 1.4

31) How much stronger is the gravitational pull of the Sun on Earth, at 1 AU, than it is on Saturn at 10 AU?
A) 5
B) 10
C) 25
D) 100
E) 250
Diff: 3
Section Ref.: 1.4

32) If the distance between two asteroids is doubled, the gravitational force they exert on each other will
A) also be doubled.
B) be half as great.
C) be one fourth as great.
D) will be 1/16 as great.
E) be four times greater.
Diff: 3
Section Ref.: 1.4

33) Because he failed to observe stellar ________, Aristotle wrongly concluded we could not be in orbit around the Sun.
Diff: 1
Section Ref.: 1.1

34) The mean distance between the Earth and Sun is called the ________.
Diff: 1
Section Ref.: 1.1

35) Ptolemy’s model was ________, with the Earth fixed in the center of the universe.
Diff: 1
Section Ref.: 1.1

36) The model of ________ used circular deferents and epicycles in a geocentric universe to explain planetary motions.
Diff: 1
Section Ref.: 1.1

37) The time for a planet to revolve around the Sun is its ________.
Diff: 2
Section Ref.: 1.1

38) When Earth overtakes Mars, the outer planet retrogrades near ________.
Diff: 2
Section Ref.: 1.1

39) The “guest star” observed by the Chinese in 1054 is now known to have been a ________.
Diff: 2
Section Ref.: 1.1
40) Galileo’s discovery of four moons orbiting ________ provided new support for the ideas of Copernicus.
Diff: 2
Section Ref.: 1.2

41) For Galileo, the observation of the phases of ________ proved that Ptolemy’s geocentric model with epicycles was wrong.
Diff: 2
Section Ref.: 1.2

42) The ________ hypothesis is that the Earth does not occupy any special place in the universe.
Diff: 3
Section Ref.: 1.2

43) The three laws of planetary motion by ________ allowed us to predict planetary motion.
Diff: 1
Section Ref.: 1.3

44) While both Ptolemy and Copernicus assumed all orbits were ________, Kepler’s first law corrected this and made planetary motion predictable.
Diff: 1
Section Ref.: 1.3

45) Kepler’s theories were based on the very accurate observations made by ________.
Diff: 2
Section Ref.: 1.3

46) According to Newton’s laws, the planets orbit the Sun due to ________.
Diff: 1
Section Ref.: 1.4

47) According to Newton, the gravity of the ________ is needed to explain planetary orbits.
Diff: 1
Section Ref.: 1.4

48) In Newton’s first law, the ________ of a body causes it to resist changes in its motion
Diff: 1
Section Ref.: 1.4
49) According to Newton’s second law, when the same force acts on two bodies, the body with the larger mass will have the ________ acceleration.
Diff: 1
Section Ref.: 1.4

50) Newton found that gravity varied with the ________ of the distance between the two bodies pulling on each other.
Diff: 2
Section Ref.: 1.4

51) How did Ptolemy explain the retrograde motion of Venus?
Answer: The epicycle for both Mercury and Venus is always centered on the Earth-Sun line, so they always orbit between us and the Sun.
Diff: 3
Section Ref.: 1.1

52) How did Ptolemy explain the retrograde motion of Mars?
Answer: Mars will retrograde on the inner portion of its epicycle, when it is closest to us and its motion on the epicycle is more obvious than its motion along its deferent.
Diff: 3
Section Ref.: 1.1

53) What “imperfections” on the Moon were visible to Galileo’s telescopes?
Answer: Impact craters, mountains, and dark lava flows, or mare.
Diff: 2
Section Ref.: 1.2

54) What is meant by the astronomical unit?
Answer: The astronomical unit, or AU, is the mean distance between the Earth and Sun.
Diff: 2
Section Ref.: 1.2

55) How did Tycho’s detailed observations of Mars’ brightness help show that its orbit could not be circular?
Answer: Tycho noted that at some oppositions, Mars was much brighter than at others, suggesting that Mars must be closer to us when it was brighter.
Diff: 3
Section Ref.: 1.1

56) What did Galileo discover through his telescope when he looked at Jupiter, and how did it refute the Ptolemaic model?
Answer: That Jupiter had four moons in orbit about it, so Earth was not the center of all things. Ptolemy contended that all things move around the Earth.
Diff: 3
Section Ref.: 1.2
57) The speed of light (and radio waves) is 300,000 km/s. How far away is a spacecraft if its radio signal takes 10 minutes to reach Earth?
Diff: 3
Section Ref.: 1.2

58) What did Galileo discover when looking at the Sun with his telescope, and how did this support Copernicus?
Answer: Sunspots, which rotated across the Sun’s face, showing that the Sun was not perfect and it (and Earth) could rotate on its axis.
Diff: 3
Section Ref.: 1.2

59) Explain how the eccentricity describes the shape of an ellipse.
Answer: The higher the eccentricity, the more elongated the oval; a circle has an eccentricity of zero, while very stretched-out comet orbits approach an eccentricity of one.
Diff: 3
Section Ref.: 1.3

60) According to Newton’s first law, if a body is moving in the absence of any net external force, describe the continuing motion of the object.
Answer: in a straight line at constant speed forever
Diff: 1
Section Ref.: 1.4

61) How do the two factors (mass and distance) in Newton’s law of gravitation each affect the force on the two bodies?
Answer: The greater the masses of the two bodies, the larger their gravity. The farther apart the bodies, the weaker this force, by the inverse square of this distance.
Diff: 2
Section Ref.: 1.4

62) Why do Newton’s Laws show a force must be acting on the planets?
Answer: The planets are moving in elliptical orbits (not a straight line). According to First Law, if no force acts on the body, it must move in a straight line. Since the planets do not, there must be a force acting on them.
Diff: 3
Section Ref.: 1.4

63) Why was Copernicus’ model much simpler than Ptolemy’s?
Answer: To duplicate retrograde motion, Copernicus merely had the planets lapping each other as they revolved around the Sun at varying speeds. Ptolemy needed a complex set of deferents and epicycles to explain retrograde motion in his geocentric model.
Diff: 2
Section Ref.: 1.1

64) Why argument did the Aristotelian school present to reject the concept of Aristarchus that the Earth could be revolving around the Sun? Why was it wrong?
Answer: Aristotle correctly concluded that if the heliocentric model were valid, we should be able to see the closer stars show parallax shift over a six-month interval as we went from one side of the Sun to the other. He failed to detect any such shifting, and thus concluded we could not be moving. Now, with powerful telescopes, we do measure the parallax shifts of the nearby stars, but this is much too tiny to be detected with the naked eye by the ancient Greeks.
Diff: 3
Section Ref.: 1.1

65) How would Ptolemy explain the rising of the Sun? Contrast this to Copernicus’ explanation of the same event.
Answer: Ptolemy would say that the celestial sphere rotated westward, carrying the Sun over our eastern horizon. Copernicus said that we, the Earth, rotate eastward once a day, and we turn to see the Sun on our eastern horizon at sunrise.
Diff: 3
Section Ref.: 1.1

66) Explain how the telescopic discoveries of Galileo could be used in support of Copernicus.
Answer: He found spots on the Sun, which moved across its face as the Sun spins; if the Sun could rotate on its axis, so could the Earth. He found craters and mare on the Moon, imperfect against the perception of heavenly perfection described by the Greeks. He noted that Venus showed an entire cycle of phases as it revolved completely around the Sun, not confined to Ptolemy’s epicycles always between us and the Sun. He found four moons around Jupiter, moving fastest when closest, and slower farther out in their orbits; this was a model of the Copernicus solar system. He resolved the Milky Way into many faint, distant stars, showing the “Celestial Sphere” of the Greeks was much vaster than Ptolemy had envisioned.
Diff: 3
Section Ref.: 1.2

67) While the Copernican model was simpler than Ptolemy’s, it was no more accurate in predicting planetary behavior at first. How did Kepler improve it?
Answer: Like Ptolemy, Copernicus believed all orbits to be perfectly circular; Kepler’s ellipses, combined with the heliocentric model, made planetary motion much more predictable.
Diff: 2
Section Ref.: 1.3

68) Explain how Kepler’s laws allow us to use the motion of an asteroid to find its average distance from the Sun.
Answer: By watching it long enough to find its period of revolution around the Sun, we can use Kepler’s third law to get the average distance by squaring the period in years, then finding the cube root of this value for the average distance of the asteroid from the Sun in astronomical units.
Diff: 3
Section Ref.: 1.3

69) According to Newton’s third law, the Voyager probes pulled just as hard on Jupiter as it did on them when they flew past it. Why were they accelerated enough to leave the solar system but Jupiter still is in orbit about the Sun?
Answer: Jupiter was much more massive than the Voyagers, so by the second law, they slowed Jupiter down a tiny bit, but it accelerated the probes so much they escaped the gravity of the Sun itself.
Diff: 3
Section Ref.: 1.4

70) How can astronomers determine the mass of the Sun?
Answer: Using Newton’s Laws, we know that gravity keeps the Earth in orbit around the Sun. Since the Earth’s path is nearly circular, we can determine the size of the force keeping it on this path. Combining this equation (for centripetal force) with the gravity equation allows astronomers to calculate the Sun’s mass.
Diff: 3
Section Ref.: 1.4

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