Astronomy: Identifying Stars and Understanding Their Coordinates and Visibility - Prof. St, Exams of Astronomy

Download Astronomy: Identifying Stars and Understanding Their Coordinates and Visibility - Prof. St and more Exams Astronomy in PDF only on Docsity! Name: ______________________________ ASTR1010 – Fall 2011 Exam #1 Multiple choice I (4 points each) Instructions: Circle what you consider to be the most appropriate answer. You do NOT need to justify your choice 1. Which of these is closest to what astronomers mean by a constellation? a) An easily recognizable grouping of stars in the sky. b) One of the twelve signs of the zodiac. c) A specific area of the sky with well-defined boundaries. d) A group of stars that form a picture. 2. Four of the prominent stars in the night sky, together with their apparent magnitudes (mv) in parentheses, are Rigel (0.12), Canopus (-0.72), Antares (1.09), and Arcturus (-0.04). Which of the following is correctly ordered from brightest to dimmest? a) Rigel, Antares, Arcturus, Canopus b) Antares, Rigel, Arcturus, Canopus c) Arcturus, Canopus, Rigel, Antares d) Canopus, Arcturus, Rigel, Antares 3. Which of the following is a reasonable definition of what astronomers refer to as the ecliptic? a) The line that divides the celestial sphere into northern and southern hemispheres. b) The point in the sky directly over your head. c) The line that the Sun follows in the sky over the course of a year. d) The angle of tilt of the Earth’s axis. 4. At local noon on the day of the summer solstice, the altazimuth coordinates of the Sun, as viewed from Cookeville, are approximately Az: 180°; Alt: 77°. Which of the following are most likely to be the Sun’s approximate coordinates at local noon on the day of the fall equinox? a) Az: 0°, Alt: 77°. b) Az: 180°; Alt: 54°. c) Az: 0°; Alt: 54°. d) Az: 180°; Alt: 77°. 2 5. The Earth’s orbit around the Sun is actually slightly elliptical. If the orbit were to become perfectly circular, what would happen to our seasons? a) They would stay about the same as they are now. b) We would have no seasons. c) The seasons would become much more extreme. d) We would still have seasons, but they would be much milder. Multiple choice - 2 (6 points each) Instructions: Circle what you consider to be the most appropriate answer and then write one or two complete sentences, draw diagrams, or both, to justify your choice. Note that you will receive only 3 points for a correct answer without any justification. Conversely it is possible to receive more than 3 points for an incorrect answer with a well-reasoned justification. 6. At local noon on which day(s) is the Sun at the zenith (directly overhead) as viewed from Cookeville? a) Only on the day of the summer solstice b) On the days of both the spring and fall equinoxes c) On all days between the spring and fall equinoxes d) The Sun is never at the zenith in Cookeville Please explain why the Sun is at the zenith on your chosen day(s), or (if you chose d), why it is never at the zenith. The Sun will only ever pass directly overhead for locations between the Tropics of Capricorn and Cancer (± 23.5° latitude). Cookeville is too far north for the Sun to ever be overhead. Even on the summer solstice, though the Sun will rise north of east and set north of west, at mid- day it will still be in the southern part of the sky. 5 9. If you could see the stars during the day this is what the sky would look just before sunset on a given day. At this time the Sun is in the middle of the constellation of Pisces. In which constellation would the Sun be located at sunrise on the NEXT day? a) Leo b) Cancer c) Gemini d) Taurus e) Pisces f) None of these Please briefly explain your reasoning. The apparent daily motion of the Sun and stars is almost entirely due really to the rotation of the Earth. This rotation means that from our point of view, both the Sun and the stars rise in the East, cross the sky, and set in the West. (See figure above) If the Sun is in the middle of Pisces when it sets then it will still be in Pisces the next day also. (The only time this might not be so is if the Sun is right at the edge of Pisces at sunset, and the very small change in position over the course of a night takes it into the next constellation by sunrise.) 6 10. During which of the following phases of the Moon would you expect the highest ocean tide? a) New Moon b) Waxing Crescent c) Third Quarter d) Waning Gibbous Briefly explain why the tide would be higher when the Moon is in your chosen phase. The gravitational attraction of the Moon causes two tidal bulges in the Earth’s oceans, on opposite sides of the Earth. The gravitational attraction of the Sun also causes two smaller tidal bulges. When the arrangement of the Earth, Sun and Moon is such that the tidal bulges of the Sun and Moon overlap with each other we get exceptionally high tides (called spring tides). For this to happen we need either the Moon and Sun on opposite sides of the Earth (which corresponds to a Full Moon) or on the same side of the Earth (which corresponds to a New Moon). In any other arrangements (or phase) the Sun’s and Moon’s tidal bulges will tend to cancel each other out, at least somewhat. 7 Essay (10 points each) Write several complete sentences to answer each question. You are encouraged to draw diagrams where appropriate. 11. Explain the difference between a lunar and a solar eclipse. What have so many more people seen a lunar eclipse than a solar eclipse? A lunar eclipse occurs when the Moon passes through the Earth’s shadow. Since this means the Moon is on the opposite side of the Earth to the Sun, this can only happen when it is a Full Moon. Since the Earth’s shadow is larger than the Moon, the whole Moon can fit into it, and remain eclipsed for a few hours as it passes through the shadow. Anyone on the night side of the Earth when this happens can just look at the Moon and see it any time during a time window of a few hours! So approximately half the Earth has the opportunity to view a lunar eclipse each time it occurs because it does not require being in a special place. A solar eclipse occurs when the Moon’s shadow passes over the Earth. Since this means the Moon is on the same side of the Earth to the Sun, this can only happen when it is a New Moon. Since the Moon is smaller than the Earth the area of the Moon’s shadow is very small when it falls on the Earth. In order to experience a total solar eclipse a person must be within this small area of the Moon’s shadow. Even within that area the eclipse experience only lasts a few minutes because the rotation of the Earth carries people out of the Moon’s shadow very quickly. So only a few people have ever been in the right place at the right time to see a solar eclipse. 10 14. Over a period of a month, we see the moon apparently change shape, going through different ‘phases’ as time progresses. Explain why we see these different phases. Let’s get one thing straight! The phases of the Moon are NOT due to the Earth blocking sunlight from reaching the Moon. This is what we call a lunar eclipse and that only happens once or twice a year, whereas the cycle of phases repeats regularly every month! The Sun shines on the Moon just as it does on the Earth. This means half the Moon is always lit up (the half facing the Sun) and the other half is always dark (the half facing away from the Sun). However, as the Moon moves round in its orbit around the Earth once every 28 days, we on Earth see a progression of phases, depending on how much of the lit side and dark side we can see from our viewpoint. For example, when the Moon is in the part of its orbit such that it is closer to the Sun than us we will see mostly the dark side and thus see either New Moon or crescent phases. However, when it moves round so that it is further from the Sun than us, we will see most or all of the lit side and thus see either a gibbous or full phase. 11 15. A keen sky watcher from Tennessee is taking a winter break in San Diego southern California. While celebrating New Year outside at midnight on Dec 31, she sees a very bright star about 45° above the southern horizon. Use one of the celestial sphere models available to you to answer the following questions about this star. To set the celestial sphere model up for southern California at midnight on Dec 31 • Set sphere so southern California is the highest point • Set Sun next to Dec 31 mark on scale on ecliptic line • Rotate sphere until Sun is at lowest below Earth – this is midnight a) Use the model to identify what star this is, and what constellation it belongs to. (Constellations are marked in UPPER CASE, stars in Proper Case.) Intended targets were Sirius in constellation of CANIS MAJOR, Procyon in CANIS MINOR, or Betelgeuse in ORION. b) What are RA/Dec coordinates of this star. Sirius: Approximately 6h45m, –17° Procyon: Approximately 7h40m, +5° Betelgeuse: Approximately 5h50m, +7° Southern Florida (on top) Sun lined up with Dec 31 on ecliptic l line scale NCP SCP Sun at lowest point below Earth represents midnight Southern horizon Look here 12 c) For approximately how many hours is this star in the visible part of the sky, as viewed from this location in southern California? Sirius: Approximately 10 hors Procyon: Approximately 12 hours Betelgeuse: Approximately 12 hours