PHYS 160 Astronomy Test #1 Name Answer Key Test Version A True False Multiple Choice 1. T 1. C 2. F 2. B 3. T 3. A 4. T 4. E 5. T 5. B 6. F 6. A 7. F 7. A 8. T 8. D 9. F 9. D 10. F 10. B 11. B 12. D Definitions 13. D 14. A 1. ecliptic 15. D 2. zodiac 16. C 3. epicycle 17. D 4. altitude 18. E 5. perihelion 19. C 6. declination 20. D 7. retrograde 21. E 8. eccentricity 22. C 9. heliocentric 23. D 10. acceleration 24. C 25. A 26. A 27. A 28. B 29. D 30. D
PHYS 160 Astronomy Test #1 Name Answer Key Test Version b True False Multiple Choice 1. F 1. A 2. F 2. B 3. F 3. A 4. T 4. C 5. F 5. E 6. T 6. B 7. F 7. C 8. F 8. B 9. T 9. A 10. T 10. D 11. A 12. D Definitions 13. B 14. D 1. acceleration 15. D 2. epicycle 16. D 3. altitude 17. A 4. aphelion 18. D 5. ecliptic 19. C 6. right ascension 20. D 7. retrograde 21. A 8. zodiac 22. D 9. eccentricity 23. E 10. geocentric or celestial sphere 24. C 25. E 26. D 27. C 28. A 29. B 30. D
Short Answers. 1. Describe how solar and lunar eclipses occur. Why do we not see eclipses twice per month? Which kind of eclipse are you more likely to see from our location in a given year Solar and Lunar eclipses. During a Lunar eclipse, the Moon must be full. During a Solar eclipse, the Moon must be new. We do not have an eclipse every new and full Moon because the Lunar orbit is tilted by 5 degrees with respect to the ecliptic. This tilt is just enough to make it very improbable that the Sun, Moon, and Earth line up directly. We are much more likely to see a lunar eclipse. Even though lunar and solar eclipses happen with roughly equal frequency, more of the Earth can see a lunar eclipse when it happens because it is visible from all dark areas of the Earth (50% of the Earth). Solar eclipses are most likely to be seen when you are near the Earth's equator. Only those people who are located in the thin strip of the Moon's umbra will be able to see the eclipse. 2. Describe what you might see in the night sky if you are in a dark location in central Arkansas facing north and you observe for several hours. Facing north, you would see a medium-bright star, Polaris, at 30 degrees above the horizon. You might also see the bright constellations cepheus (shape of a house), cassiopeia (shape of a W), draco (dragon), the big dipper (shape of a ladle), and the little dipper. As you observe these constellations over several hours, you will see them appear to rotate in a counter clockwise direction with Polaris in the center. The stars within 30 degrees of Polaris will never drop below the horizon, so they are called "circumpolar". The rest of the stars will appear to rise in the east and set in the west. The apparent CCW rotation of the night sky around Polaris is due to the rotation of Earth on its axis once per Earth day. The sky is actually fixed and it is the observer that is rotating. 3. Explain the statement: The farther away we look in distance, the further back we look in time. All light travels at a constant velocity in the vacuum of space. Light from distant objects takes a finite amount of time to reach our eyes/detectors on Earth. The farther the distance between the object and Earth, the longer it took the light to reach our eyes. For example, the light from an object that is 100 light-years away took 100 years to reach our eyes. We are therefore viewing the object as it existed 100 years ago. Even light from our own Sun takes 7 minutes to reach our eyes. If the Sun exploded now, we would not know about it for 7 minutes. 4. How do the following motions affect the position of objects in our sky: Earth s rotation on an axis defined by the north and south poles, Earth s rotation around the Sun, the rotation of the Moon around the Earth, precession?
Earth s rotation on axis: causes all heavenly objects (Moon, Sun, stars, planets) to appear to rise in the east and set in the west. In the northern sky, Polaris appears to stand still and all stars within an angle equal to your latitude will not appear to set, but instead will move in a circle, called circumpolar. Earth s rotation around Sun: due to Earth s axis tilt, we get seasons. Also, different stars are visible in the night sky at different times of the year in the East-west directions: zodiac constellations. Rotation of Moon around Earth: phases of the Moon, eclipses Precession: Earth s NCP will point to different stars as the rotation axis of north slowly (1 cylcle in 26,000 years) precesses. NCP will be at Vega in 13,000 years. 5. Is the far side of the Moon the same as the dark side of the Moon? Explain. No. The Moon is phase locked in its orbit with Earth. That means that it rotates exactly once on its axis during its rotation around Earth. The consequence is that there is one side of the Moon that always faces Earth. We will define that as the "near side" and define the other side, the side that Earth never sees as the "far" side. Now, let's examine which side of the Moon is "dark". Half of the Moon is always bathed in sunlight and half of the Moon is always dark. The side that faces the Sun is the bright side. In its path around the Earth, all sides of the Moon are lit for exactly half of the cycle. That means that if you lived on the Moon, you would have approximately 14 Earth-days of daylight and 14 Earth-days of night-time each month. Therefore, there is no side of the Moon that is always dark and no side that is always lit. During the Full phase, the far side of the Moon is the dark side. During the New phase, the far side is the brightly lit side and the "near" side is the dark side. 6. What is meant by a geocentric universe? Name the three scientists who played the primary roles in overturning the geocentric viewpoint. Describe their main contributions to astronomy. Ptolemey proposed the first model of the universe, which was Geocentric (Earth-centered). The model explained planet retrograde motion with epicycles and deferents. His theory lasted over 1000 years. People who helped overturn the geocentric model: Copernicus: Proposed the first heliocentric (Sun-centered) model of the universe. Explained the retrograde motion without the need of epicycles. Galileo: with the aid of the first known telescope, he discovered the four large mons of Jupiter, phases of Venus and imperfections in the heavens such as craters on the Moon. His discoveries
helped to debunk the geocentric model because if moons were orbiting Jupiter, they could not also be orbiting Earth. Also, phases of Venus can only be caused by Venus orbiting the Sun. Brahe: Made incredibly detailed observations of the planetary motion over a period of several years. Kepler: 3 laws of motion as detailed above. Mathematically described motion of planets around the Sun that exactly matched observations. Newton: 3 laws of Physics and the theory of Universal Gravity. He proved mathematically that if the Sun and planets were held together by gravity, the orbits would be precisely as described by Kepler.