AST 207 Test 1Answers 29 September 2010 1 of 3 You may use one sheet of notes. You may not use books or additional notes. Do the easy questions first. Then go back to the harder ones. Planet Period(yr) Semi-major axis (AU) EccentricityMercury 0.241 0.387 0.206 Venus 0.615 0.723 0.007 Earth 1.000 1.000 0.017 Mars 1.881 1.523 0.093 Jupiter 11.86 5.202 0.049 Saturn 29.46 9.539 0.056 Name PID 1 / 52 / 43 / 84 / 6Total / 23AST 207 Test 1Answers 29 September 2010 2 of 3 1. Galileo disproved Ptolemy’s geocentric model by observing the phases of Venus. He wrote, “(1) Know therefore that about 3 months ago I began to observe Venus with the instrument, and I saw her in a round shape and very small. Day by day she increased in size and maintained that round shape until finally, attaining a great distance from the Sun, the roundness of her eastern part began to diminish, and (2) in a few days she was reduced to a semicircle. She maintained this shape for many days, all the while, however, growing in size. (3) At present, she is becoming sickle-shaped.” a. (2 pt.) What did Galileo observe that contradicted Ptolemy’s model? Galileo observed that Venus was in the full phase. b. (1 pt.) Why did Ptolemy not disprove his own model in the same way? Ptolemy did not have a telescope, which is needed to see phases. c. (2 pt.) Draw a diagram that shows Venus at the time (2) of his observations. You must include the sun and earth. For simplicity, you may let earth be stationary. Explain your placement of Venus in your diagram. Put Venus so that the boundary between the sunlit and dark halves is along the line between earth & Venus. It is below because it is getting closer to earth. 2. Copernicus wrote On the Revolutions of the Heavenly Spheres. a. (2 pt.) What did he propose in this book? Copernicus proposed that the planets, including earth moved around the sun. b. (2 pt.) What did he mean by “revolutions”? What did he mean by “heavenly spheres”? Revolutions refer to the orbits, and heavenly spheres are planets. 3. The drawing on the front page shows the constellations of the Zodiac. Suppose the date is 3/21 and sunrise and sunset occur at 6am and 6pm. a. (2 pt.) Which constellation is rising at sunset? You must explain how you found the answer, either in words or with a drawing, to receive any credit. At sunset, the horizon is in the line from Pisces to Virgo. Since the earth turns counterclockwise, more of Virgo will be seen later: Virgo is rising. b. (3 pt.) Which constellation(s) can you not see at any time during the night? Explain how you found your answer. You cannot see Pisces, the constellation in the direction of the sun. You can see Aries, because its center rises 2 hours after sunset. You can also see Aquarius, because its center rises 2 hours before sunrise. c. (2 pt.) Explain why the earth spins more than 360 from noon on one day to noon on the next day. Hint: Consider how much earth must spin in 90 days, and show that it is more than 90×360. (1 pt.) How many degrees does the earth spin between successive noons? earth sun Dark side, venus Visible sideAST 4. Adi207 Considdiagraat noon360 inAstronomers distance of 0.5a. (3 pts.The mmajor the drab. (3 pts.(You afound The peLaw. Tlook ata slighthe comder noon on 3m you are stan on 6/21. Ean a day; morediscovered a n5AU and the s) Find the lenmajor axis is 20axis is 10.5Aawing. ) Is it likely toare 20 years oyour answer.eriod can be fThe period is t the table on htly shorter semet’s period Tes3/21 and noonanding on the arth turned 90e precisely, it new comet, ansecond focus ngth of the ma0+2×0.5=21AAU. The relatio return in yoold.) Explain h found from K34years. Quithe front pagemi major axiis slightly lonst 1Answers3 of 3n on 6/21, appleft side of ea0 full turns andis 360+360/3nd they foundof its orbit is ajor axis. AU. The semionship is fromour lifetime? how you Kepler’s 3rd cker way is toge. Saturn hass. Therefore nger than 29yproximately 9arth at noon od an extra 90365.25=360.9d that it passe20AU from ti m o s years, which is29 Sep90 days later. on 3/21 and o. Therefore e99. s closest to ththe sun. s within my lptember 201On the on the bottom earth turns he sun at a ifetime.
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