Exam 1 Astronomy 114. Part 1

Transcription

1 Exam 1 Astronomy 114 Part 1 [1-40] Select the most appropriate answer among the choices given. 1. If the Moon is setting at 6AM, the phase of the Moon must be (A) first quarter. (B) third quarter. (C) full. (D) new. (E) waning crescent. 2. One light year is (A) the distance from the Earth to the Moon. (B) 1 million kilometers. (C) the distance light travels in one year. (D) the distance from the Earth to the Sun. (E) the time it take light to go around the Sun once. 3. If you wanted to find Uranus in the night sky, you d look for it near (A) the zodiac. (B) the celestial pole. (C) the celestial equator. (D) the zenith. (E) the horizon. 4. One astronomical unit (AU) is (A) the distance from the Earth to the Moon. (B) 1 million kilometers. (C) 10 light years. (D) the distance from the Earth to the Sun. (E) the diameter of the Milky Way. 5. The Sun sets at different location along the western horizon each day because (A) the Earth is stationary. (B) the stars rotate with the celestial sphere. (C) the tilt of the Earth changes throughout the year. (D) the position of the Sun along the ecliptic is constantly changing. (E) the Sun always sets exactly due west. 6. An astronaut inside the Space Station experiences weightlessness because (A) there is no gravity in space. (B) gravity is extremely weak so far away from the Earth. (C) gravity of the Earth is canceled exactly by the gravity of the Space Station. (D) the Space Station has an anti-gravity device. (E) the Space Station is in a constant state of free-fall. 1

2 7. At which lunar phase(s) the highest high tides occur? (A) first quarter (B) new moon (C) full moon (D) both new and full moons (E) both first and third quarters 8. Which of the Galileo s discoveries challenged the belief that the Earth is the center of the Universe? (A) sunspots (B) moons of the Jupiter (C) phases of the Venus (D) all of above (E) only (B) and (C) 9. Why is a synodic month 2 days longer than a sidereal month? (A) Our calendar was invented too long ago and is no longer accurate. (B) The Earth travels about 30 degrees around the Sun in each month, and this adds 2 days between new moons. (C) One full Earth rotation takes less than 24 hrs, and it adds up to about 2 days in one month. (D) The Moon s orbit around the Earth is not perfectly circular. (E) The Earth rotation axis is tilted by 23.5 degrees. 10. On the days of the vernal and autumunal equinoxes, the length of day and night are the same (A) at the equator. (B) at the Tropic of Cancer. (C) everywhere north of the Tropic of Cancer. (D) everywhere north of the equator. (E) everywhere on the Earth. 11. A newly designed space shuttle weighs twice as much as the old one. How would its escape velocity compare with the older design? (A) the same (B) 2 times larger (C) 2 times larger (D) 4 times larger (E) 10 times larger 12. While a 2-ton elephant was out for an evening walk at a speed of 5 miles per hour, a mice jumps out of the bushes and scares the elephant into a 15 miles per hour trot. How did the elephant s kinetic energy change? (A) kinetic energy increased by a factor of 3 (B) kinetic energy increased by a factor of 9 (C) kinetic energy decreased by a factor of 3 (B) kinetic energy decreased by a factor of 9 (E) kinetic energy did not changed 13. Thermal radiation is defined as (A) radiation produced by a hot object. (B) radiation in the infrared part of the electromagnetic spectrum. (C) radiation that depends only on the temperature of the emitting object. (D) radiation that is felt as heat. (E) all of above. 2

3 14. Seasons are caused by (A) the change in Earth s distance from the Sun. (B) the Sun s changing brightness during the sunspot cycle. (C) one side of the Sun being cooler than the other. (D) Moon s shadow on Earth. (E) the Earth s rotation axis being tipped so that first one hemisphere and then the other receives sunlight more directly. 15. Lunar eclipse happens only during (A) full moon. (B) blue moon. (C) half moon. (D) crescent moon. (E) new moon. 16. If the radius of the Earth were to double with no change in its mass, your weight would (A) be unchanged. (B) 4 times larger. (C) be twice as large. (D) 1/2 as large as now. (E) 1/4 as large as now. 17. Which of the following is the reason for the solar day being longer than a sidereal day? (A) precession of the Earth s axis. (B) the tilt of the Earth s axis. (C) the combined effect of the rotation of the Earth and its orbit about the Sun. (D) the Earth year being a non-integral number of Earth days. (E) the non-circular orbit of the Earth around the Sun. 18. Why does the length of day time change with season? (A) The Earth spins slower when it is hot outside. (B) The Earth spins slower when it is closer to the Sun. (C) When closer to the Sun, the Earth moves around the Sun at a higher speed because of stronger gravity. (D) The Earth rotation axis is tilted about the ecliptic. (E) The length of a day does not change, but the brightness of the Sun changes with season. 19. All of the following statements are true. Which one explains the reason why a solar eclipse does not occur at every new moon? (A) The nodes of the Moon s orbit precess with an 18-year period. (B) The orbital plane of the Moon is tilted by about 5 to the ecliptic plane. (C) The Moon rotates synchronously with its revolution about the Earth. (D) The sidereal month is shorter than the lunar month. (E) The Moon is the primary cause of tides on the Earth. 20. What is an epicycle supposed to explain? (A) Solar eclipses. (B) Seasons. (C) Precession. (D) Phases of the Moon. (E) Retrograde motion of the planets. 3

4 21. On the day the Moon s phase is new, what phase would the Earth have as viewed from the Moon? (A) Full (B) First Quarter (C) Last Quarter (D) New (E) Waxing gibbous 22. When a comet comes close to the Sun, it must move faster because (A) energy is conserved. (B) it is too hot. (C) because Kepler s First Law says so. (D) it does not move faster. (E) both (A) & (C) are correct. 23. At the Earth equator, the Sun is directly overhead (A) everyday. (B) once in a blue moon. (C) only once a year. (D) only twice a year. (E) at no time during a year. 24. We can see each other in the classroom right now because we (A) emit thermal radiation. (B) emit visible light. (C) emit infrared light. (D) reflect visible light. (E) reflect infrared light. 25. Radio waves differ from visible light in that they (A) travel much faster through empty space. (B) travel much slower through empty space. (C) have a much longer wavelength. (D) have a much shorter wavelength. (E) are not electromagnetic waves like light is. 26. Astronomers can measure what stars are made of by (A) seeing what spectrum lines they show. (B) weighing the light they emit. (C) measuring the speed of the light they emit. (D) weighing them using Kepler s law. (E) measuring how fast they are moving. 27. If the Earth were to shrink to one half of its present size with no change in its mass, your weight would (A) be unchanged. (B) 4 times larger. (C) be twice as large. (D) 1/2 as large as now. (E) 1/4 as large as now. 4

5 28. Which of the following never goes in retrograde motion? (A) Sun (B) Venus (C) Mars (D) Jupiter (E) Saturn 29. During a lunar eclipse, Earth, Sun, and Moon are lined up as (A) Sun Earth Moon (B) Sun Moon Earth (C) Earth Sun Moon (D) Moon Sun Earth (E) none of above. 30. You are standing on a scale in an elevator. Suddenly you notice your weight decreases. What do you conclude? (A) The elevator is accelerating upwards. (B) The elevator is moving at a constant velocity upwards. (C) The elevator is accelerating downwards. (D) The elevator is moving at a constant velocity downwards. (E) Your diet is working. 31. From Kepler s third law, a hypothetical planet that is twice as far from the Sun as the Earth should have a period of (A) 1/2 Earth year. (B) 1 Earth year. (C) 2 Earth year. (D) more than 2 Earth year. (E) it depends on the planets mass. 32. The Greeks have considered a heliocentric system a plausible cosmological model, but they rejected it because (A) they could not feel the spin of the Earth. (B) they did not see the parallax of the stars. (C) they could not explain the phase of the Moon this way. (D) they did not think Gods would fling us off to a distant rock far away from the center. (E) it was just a bad outcome in a coin toss. 33. Saturn is on average 10 AU from the Sun. What is the approximate orbital period of Saturn? (A) 10 years. (B) 32 years. (C) 100 years. (D) 1000 years. (E) There is not enough information. 34. Which of the following photons have the most energy? (A) X ray. (B) visible light. (C) infrared. (D) ultraviolet. (E) radio 5

6 35. The stars seen at night slowly change over the course of the year, this is because (A) the Earth rotates on its axis. (B) the Earth orbits about the Sun. (C) the Moon orbits the Earth. (D) the planets orbit the Sun. (E) You always see the same stars at night. Only your location on Earth matters. 36. Which of the following best describes the origin of ocean tides on Earth? (A) Tides are caused by difference in the force of gravity exerted by the Moon across the sphere of the Earth. (B) The Moon s gravity pulls harder on water than on land because water is less dense than rock. (C) Tides are caused by the tilt of the Earth s rotation axis. (D) Tides are caused primarily by the gravitational force of the Sun. (E) Tides are caused on the side of the Earth nearest the Moon because the Moon s gravity attracts the water. 37. Everything looks red through a red filter because (A) the filter emits red light and absorbs other colors. (B) the filter absorbs red light and emits other colors. (C) the filter transmits red light and absorbs other colors. (D) the filter reflects red light and transmits other colors. (E) your brain is tricked into thinking that everything should look red. 38. The amount of time between successive passes of the star Sirius across the meridian is (A) 23 hours 56 minutes. (B) 24 hours. (C) days. (D) 12 years. (E) 26,000 years. 39. The heliocentric model predicts that the nearest stars should appear to move with respect to the more distant stars because of parallax. Why was this not observed until recently? (A) Nobody thought of this test until recently. (B) All of the stars move together in the sky, confusing the situation. (C) Distant stars are too faint to see. (D) Using a telescope to stare at heavily bodies was considered dangerous. (E) Stars are too far away to produce measurable parallax with a naked eye. 40. Suppose you see two stars: a blue star and a red star. What can you conclude about the two stars? (A) The red star is more massive than the blue star. (B) The blue star is more massive than the red star. (C) The blue star is farther away than the red star. (D) The blue star has a hotter surface temperature than the red star. (E) The red star has a hotter surface temperature than the blue star. 6

7 Part 2 NAME: SPIRE ID: Write your name and ID number first. Answer any four of the following five questions to your best ability. If you answer all five, the best four scores will be counted. 41. You are planning on spending your spring break in Hawaii. As an astronomy enthusiast, you Googled and found that the latitude of Mauna Kea, Hawaii is about +19. (a) The declination of the Large Magellanic Cloud is about 60. Would you be able to see it if you are camping at night on the south facing beach on Maui? Why or why not? (b) On March 22, you are planning to celebrate the Spring Equinox on the summit of Mauna Kea. What s the declination of the Sun on this date? and what elevation would the Sun transit at noon? 42. Lunar eclipse is seen almost everywhere on Earth while a solar eclipse is seen more rarely. Draw a diagram describing the geometry of the Sun, Moon, and the Earth in each case and explain why the solar eclipse is so rarely witnessed. 7

8 43. A planet or a companion star in orbit around another star remains in orbit because the gravitational force is compensated exactly by the centrifugal force, so that there is no net force between the bodies. Starting from the Newton s law of gravitation and centripetal force (F c = mv 2 /R, where m is the mass of a body going around in orbit), derive the generalized (Newton s) version of Kepler s Third Law, P 2 = (4π 2 /GM)R 3, where P and R are a period and the average radius of the orbit, M is the mass of the central star, and G is the gravitational constant. 44. You are a 300 K blackbody, and your thermal radiation spectrum peaks around 10 micron (10000 nm). After discovering a mysterious object in space, you scan the light emitted by this object and learn that its radiation spectrum peaks at 3 nm. What would you conclude from that? 45. Oxygen atom has a bright infrared line at a wavelength near 60 micron. You think you just discovered a galaxy that is traveling toward you at 1/2 the speed of light. To verify this is true, at what wavelength should you detect this emission line to confirm your hypothesis about the galaxy s motion? [Make sure that your answer actually makes sense.] 8