## Astronomy 2: 1.2

 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 __________. 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 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? at noon When would a new Venus be highest in the sky? at noon When would you expect to see Venus high in the sky at midnight? never 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? We sometimes see gibbous (nearly but not quite full) Venus. The place in a planet’s orbit that is closest to the Sun is called: perihelion. Kepler’s second law implies what about planetary motion? A planet moves faster when it is closer to the Sun. It was the Chinese who provided critical ancient data on supernovae and comets. True The principal culture that transferred Greek astronomical knowledge to Renaissance Europe was: Islamic The most accurate Greek attempt to explain planetary motion was the model of: Ptolemy The Ptolemaic model probably persisted for all these reasons EXCEPT: it accounted well for Galileo’s observations of the phase cycle of Venus. The greatest contribution of the Greeks to modern thought was: the development of scientific inquiry and model building. The Ptolemaic model of the universe: explained and predicted the motions of the planets with deferents and epicycles. According to Copernicus, retrograde motion for Venus must occur around: inferior conjunction, when it passes between us and the Sun. Combining Newton’s and Kepler’s laws, we can weigh the Sun, provided we know: the size of the A.U. and exact length of the year. When a planet retrogrades, it appears to move westward for weeks at a time. True Like the Sun and the Moon, the planets appear to move from west to east from one day to the next. True Like the Sun and the Moon, the stars appear to move from west to east from one day to the next. True Scientists today do not accept the Ptolemaic model because: the work of Tycho and Kepler showed the heliocentric model was more accurate. On which of these assumptions do Ptolemy and Copernicus agree? All orbits must be perfect circles. The heliocentric model was actually first proposed by: Aristarchus. According to Copernicus, the retrograde motion for Mars must occur: at opposition, when the Earth overtakes Mars and passes between Mars and the Sun. Which was a contribution to astronomy made by Copernicus? He laid out the order and relative motion of the known solar system. Which of these was NOT a part of the original Copernican model? Mercury speeds up at perihelion, and slows down at aphelion. Which of the statements below is part of both the Ptolemaic and Copernican models? The Moon orbits the Earth once a month. As originally stated, the Copernican model did no better job of predicting planetary behavior than did the Ptolemaic one. True Which of these was NOT seen telescopically by Galileo? Stellar parallax Which of the following was NOT a contribution of Galileo to astronomy? The changing appearance of Saturn’s rings corresponds to our seasons. Which of the following is a contribution to astronomy made by Galileo? All of the above. Which of these observations of Galileo refuted Ptolemy’s epicycles? the complete cycle of Venus’ phases Which of these was NOT a telescopic discovery of Galileo? the moons of Saturn A fatal flaw with Ptolemy’s model is its inability to predict the observed phases of: Mercury and Venus. It took two centuries for the Copernican model to replace the Ptolemaic model because: there was no scientific evidence to support either model until Galileo made his observations. Galileo found the rotation period of the Sun was approximately: a month. 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. True Galileo’s observations of sunspots proved the Sun was rotating, like the Earth. True Kepler’s first law worked, where Copernicus’ original heliocentric model failed, because Kepler described the orbits as: elliptical, not circular. Tycho Brahe’s contribution to Kepler’s Laws of Planetary Motion was: his detailed and accurate observations of the planet’s position. The most famous prehistoric astronomical observatory is: Stonehenge A circular orbit would have an eccentricity of: 0. Upon which point do Copernicus and Kepler disagree? The orbits of the planets are ellipses, with one focus at the Sun. What contribution to astronomy was made by Tycho Brahe? His observations of planetary motion with great accuracy proved circular orbits could not work. Which concept was NOT a part of Kepler’s Laws of Planetary Motion? Epicycles are needed to explain the varying brightness of the planets. According to Kepler’s third law, the square of the planet’s period in years is: proportional to the cube of its semimajor axis in A.U. What does Kepler’s third law imply about planetary motion? Planets further from the Sun orbit at a slower speed than planets closer to the Sun. A planet whose distance from the Sun is 3 A.U. would have an orbital period of how many Earth-years? Square root of 27 Kepler found the orbits of planets are ellipses, not circles. True The orbits of most of the planets in our solar system have eccentricities close to zero. True Kepler based his theories on the precise planetary observations of Tycho Brahe. True The eccentricity of a perfectly circular orbit is 1. False Kepler determined the shape of each planet’s orbit by triangulation from different points on Earth’s orbit, using observations made at many different times of the year. True Mercury, with a higher eccentricity orbit, should change its orbital speed more than do Venus or Earth. True A planet (or comet) will speed up as it approaches the Sun. True Transits of Venus were critical in early determinations of the A.U. True Newton’s modification of Kepler’s Third Law lets us measure the mass of the Sun. True During the eighteenth and nineteenth centuries, attempts to precisely measure the astronomical unit relied largely on rare: transits of the inferior planets across the Sun. Today we rely largely on what technique to precisely measure distances in the solar system? radar echo timings The force of gravity varies with the: Both A and C are correct. The Law of Universal Gravitation was developed by: Newton. The force of gravity between two objects: increases with the masses of the bodies, but decreases with the square of the distances between them. 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: decrease by a factor of 9. How much stronger is the gravitational pull of the Sun on Earth, at 1 AU, than it is on Saturn at 10 AU? 100X Which of these was a contribution of Newton to astronomy? All of these were due to Newton’s work. Geosynchronous satellites orbit at about four Earth radii, where the Earth’s gravitational pull is: 1/16 g. Jupiter lies about 5 A.U. from the Sun, so at its distance: the Sun’s gravity is 25 times weaker than its pull on the Earth. How does Newton’s Universal Law of Gravitation explain Kepler’s laws? Both C and D are correct. 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: the same as you do here. If the distance between two asteroids is doubled, the gravitational force they exert on each other will: be one fourth as great. Newton’s Law of Gravity would explain why Saturn, so far from the Sun, moves so slowly across the sky. True If the mass of a body were doubled, its gravity would become 4 times stronger. False According to Newton’s second law, if you double the force acting on a body, the acceleration will double. True Compared to orbital velocity, escape velocity is about: 40% more. Orbital speed is the speed with which a planet moves around the Sun. This speed is determined by: the mass of both the planet and the Sun and the distance between the two. Escape velocity is the speed required to: overcome the gravitational pull of an object. Modern scientific theories are NOT: perfect.