Astronomy Chapter 2 Quiz Q&As – Flashcards
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Upon which point do Copernicus and Kepler disagree?
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The orbits of the planets are ellipses, with one focus at the Sun.
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The greatest contribution of the Greeks to modern thought was:
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the development of scientific inquiry and model building.
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The force of gravity between two objects:
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increases with the masses of the bodies, but decreases with the square of the distances between them.
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Jupiter lies about 5 A.U. from the Sun, so at its distance:
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the Sun's gravity is 25 times weaker than its pull on the Earth.
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Which of these was a contribution of Newton to astronomy?
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All of these were due to Newton's work.
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Which of these observations of Galileo refuted Ptolemy's epicycles?
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the complete cycle of Venus' phases
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Given that the planet orbiting the nearby star 51 Pegasi is about 20X larger than the Earth, but 400X more massive, on that world you would weigh:
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the same as you do here
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Which was a contribution to astronomy made by Copernicus?
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His observations of planetary motion with great accuracy proved circular orbits could not work.
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What contribution to astronomy was made by Tycho Brahe?
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His observations of planetary motion with great accuracy proved circular orbits could not work.
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Which of the following is a contribution to astronomy made by Galileo?
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All of the above are correct.
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Orbital speed is the speed with which a planet moves around the Sun. This speed is determined by
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the mass of both the planet and the Sun and the distance between the two.
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Which of these was NOT a telescopic discovery of Galileo?
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stellar parallax
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What does Kepler's third law imply about planetary motion?
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Planets further from the Sun orbit at a slower speed than planets closer to the Sun
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According to Kepler's third law, the square of the planet's period in years is:
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proportional to the cube of its semimajor axis in A.U.
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In what geometric way can we determine the absolute distances to the planets? (SA)
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The parallax for some nearby planet can be directly measured, giving a precise knowledge of A.U. This is now set from direct radar echo timings off the surfaces of the Sun and other planets.
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What relationship did Newton find between orbital and escape velocities? Relate this to the staging of the Apollo missions, first to a parking orbit about the Earth, and then on to the Moon. (SA)
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The escape velocity is greater than the orbital velocity by the square root of two. Thus the Apollo missions were first placed into Earth orbit, and from there an upper stage ignited to give them extra speed to break our gravitational hold.
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A planet whose distance from the Sun is 3 A.U. would have an orbital period of how many Earth-years?
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?27
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Today we rely largely on what technique to precisely measure distances in the solar system?
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radar echo timings
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Combining Newton's and Kepler's laws, we can weigh the Sun, provided we know:
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the size of the A.U. and exact length of the year.
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The force of gravity varies with the
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Both A and C are correct.
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Which of these was NOT seen telescopically by Galileo?
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the moons of saturn
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Compared to orbital velocity, escape velocity is about:
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40% more
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The principal culture that transferred Greek astronomical knowledge to Renaissance Europe was:
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Islamic
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The place in a planet's orbit that is closest to the Sun is called
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perihelion
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It took two centuries for the Copernican model to replaced the Ptolemaic model because
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there was no scientific evidence to support either model until Galileo made his observations.
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According to Copernicus, retrograde motion for Venus must occur around
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inferior conjunction, when it passes between us and the Sun
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According to Newton's Law of Universal Gravitation, if the Moon were three times further from Earth, the force by Earth on the Moon would
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Decrease by a factor of 9
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How does Kepler's First Law refine the Copernican model greatly?
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Copernicus, like the Greeks, thought all orbits were circular. But when Kepler used elliptical orbits, particularly with Mars and Mercury, the theory fit the actual observations of planetary motion much better than did the old Ptolemaic one.
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Which of these was NOT a part of the original Copernican model?
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Mercury speeds up at perihelion, and slows down at aphelion.
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Which concept was NOT a part of Kepler's Laws of Planetary Motion?
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Epicycles are needed to explain the varying brightnesses of the planets.
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Tycho Brahe's contribution to Kepler's Laws of Planetary Motion were
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his detailed and accurate observations of the planet's position.
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On which of these assumptions do Ptolemy and Copernicus agree?
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All orbits must be perfect circles.
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Of the Ptolemaic and Copernican models, who wins the battle of Occam's Razor for the simplest explanation of retrograde motions? (also explain what is Occam's Razor)
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Copernicus simply had retrograde motion resulting from the different speeds of the planets, with retrograding occurring any time one planet overtook another. Ptolemy by contrast needed complex deferents, epicycles, and equants to handle the complex planetary motions.
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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?
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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.
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The Ptolemaic model probably persisted for all these reasons EXCEPT:
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it accounted well for Galileo's observations of the phase cycle of Venus.
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A fatal flaw with Ptolemy's model is its inability to predict the observed phases of
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Mercury and Venus
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Kepler's second law implies what about planetary motion?
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A planet moves faster when it is closer to the Sun.
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According to Copernicus, the retrograde motion for Mars must occur
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at opposition, when the earth overtakes Mars and passes between Mars and the Sun.
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Which of these was NOT a telescopic discovery of Galileo?
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the moons of saturn
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The Ptolemaic model of the universe:
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explained and predicted the motions of the planets with deferents and epicycles.
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The heliocentric model was actually first proposed by:
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Aristarchus.
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Galileo found the rotation period of the Sun was approximately
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a month
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How does Newton's Universal Law of Gravitation explain Kepler's laws?
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Both C and D are correct. Also, the work of Tycho and Kepler showed the heliocentric model was more accurate.
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Geosynchronous satellites orbit at about four earth radii, where the earth's gravitational pull is:
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1/16 g.
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Which of the statements below is part of both the Ptolemaic and Copernican models?
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The moon orbits the Earth once a month
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A fatal flaw with Ptolemy's model is its inability to predict the observed phases
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Mercury and Venus
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The most accurate Greek attempt to explain planetary motion was the model of:
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Ptolemy.
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Explain how Kepler's laws allow us to use the motion of an asteroid to find its average distance from the Sun. (SA)
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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.
