AST 135 Unit 2 – Flashcards
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Question :In Ptolemy's Earth-centered model for the solar system, Venus's phase is never full as viewed from Earth because it always lies between Earth and the Sun. In reality, as Galileo first recognized, Venus is __________.
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full whenever it is on the opposite side of the Sun from Earth, although we cannot see the full Venus because it is close to the Sun in the sky
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In Ptolemy's Earth-centered model for the solar system, Venus's phase is never full as viewed from Earth because it always lies between Earth and the Sun. In reality, as Galileo first recognized, Venus is __________.
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A full Venus always occurs when it is on the opposite side of the Sun as viewed from Earth. (However, we cannot see the full Venus, because it is always very close to the Sun in the sky at that time.) Galileo used this fact as evidence for the Sun-centered view of the solar system: The fact that Venus goes through all the phases must mean it goes all the way around the Sun. In contrast, in the Ptolemaic model, Venus only varies between new and crescent phases
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Imagine that Venus is in its full phase today. If we could see it, at what time would the full Venus be highest in the sky?
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noon (Because Venus is full when it is on the opposite side of the Sun from Earth, the Sun and Venus both appear to move through the sky together at that time. Venus therefore rises with the Sun, reaches its highest point at noon, and sets with the Sun.)
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When would a new Venus be highest in the sky?
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Noon (A new Venus occurs when Venus is directly between the Sun and Earth, which means a new Venus will be highest in the sky at the same time that the Sun is highest in the sky, which is around noon (local time).)
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When would you expect to see Venus high in the sky at midnight?
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Never, For Venus to be high in the sky at midnight, it would have to be on the opposite side of our sky from the Sun. But that never occurs because Venus is closer than Earth to the Sun.
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In Ptolemy's Earth-centered model for the solar system, Venus always stays close to the Sun in the sky and, because it always stays between Earth and the Sun, its phases range only between new and crescent. The following statements are all true and were all observed by Galileo. Which one provides evidence that Venus orbits the Sun and not Earth?
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We sometimes see gibbous (nearly but not quite full) Venus. (In the Ptolemaic system, we should never see more than a crescent in Venus. Because we do in fact see more, the Ptolemaic model must be wrong. The full range of phases that we see for Venus is consistent only with the idea that Venus orbits the Sun. Galileo was the first to observe the phases of Venus — and hence to find this evidence in support of the Sun-centered system — because he was the first to observe Venus through a telescope. Without a telescope, we cannot tell that Venus goes through phases.)
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Earth is slightly closer to the Sun in January than in July. How does the area swept out by Earth's orbit around the Sun during the 31 days of January compare to the area swept out during the 31 days of July?
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Both areas are the same, Kepler's second law tells us that a planet always sweeps out equal areas in equal times. Therefore, Earth sweeps out the same area in any 31-day period, no matter what month it is.
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All of the following statements are true. Which one can be explained by Kepler's second law?
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Mars moves faster in its orbit when it is closer to the Sun than when it is farther from the Sun.
(Kepler's second law tells us that a planet moves faster in its orbit when it is closer to the Sun (near perihelion) than when it is farther (near aphelion). This law applies to all planets and therefore explains the statement about Mars.)
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Jupiter orbits the Sun at an average distance of 5.203 AU and takes 11.86years to complete each orbit. Based on these facts, which statement is true?
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11.862=5.2033
Kepler's third law can be stated mathematically as p2=a3, where p is the planet's orbital period in years and a is its average orbital distance in AU.
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You discover an asteroid that orbits the Sun with the same 1-year orbital period as Earth. Which of the following statements must be true?
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The asteroid's average (semimajor axis) distance from the Sun is 1AU.
Kepler's third law tells us that an object's average orbital distance can be calculated from its orbital period using the formula p2=a3 (where p is the planet's orbital period in years and a is its average orbital distance in AU). Therefore, all objects that share Earth's orbital period of 1 year must also share Earth's average orbital distance of 1AU.
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All of the following statements are true. Which one can be explained by Kepler's third law?
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Venus orbits the Sun at a faster orbital speed than Earth.
(Kepler's third law can be stated as the precise mathematical relationship p2=a3; (where p is the planet's orbital period in years and a is its average orbital distance in AU). The essence of the law, however, is that it means planets closer to the Sun orbit at faster average speeds than planets farther from the Sun. Therefore, Venus orbits at a faster orbital speed than Earth, because Venus is closer to the Sun.)
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KNOW THESE:
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-Earth is slightly closer to the Sun in January than in July.
-Mars moves faster in its orbit when it is closer to the Sun than when it is farther from the Sun.
-The Sun is not in the precise center of Saturn's orbit.
-All the planets orbit the Sun in nearly the same plane.
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Kepler's first law states that the orbit of each planet is an ellipse with the Sun at one focus. Which of the following statements describe a characteristic of the solar system that is explained by Kepler's first law?
Check all that apply.
All the planets orbit the Sun in nearly the same plane.
The Sun is located slightly off-center from the middle of each planet's orbit.
Earth is slightly closer to the Sun on one side of its orbit than on the other side.
Inner planets orbit the Sun at higher speed than outer planets.
Pluto moves faster when it is closer to the Sun than when it is farther from the Sun.
Venus orbits the Sun faster than Earth orbits the Sun.
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The Sun is located slightly off-center from the middle of each planet's orbit.
Earth is slightly closer to the Sun on one side of its orbit than on the other side.
