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Chico GEOS 142 - Planetarium Lab #2: Variations in the Sky With Latitude & Season

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Planetarium Lab #2: Variations in the Sky With Latitude & Season© 2002 Ann Bykerk-Kauffman, Dept. of Geological and Environmental Sciences, California State University, Chico**Supported by NSF Grant #9455371. Permission is granted to reproduce this material for classroom use.C–41IntroductionUp until this point, we have spent our time in the planetarium focusing on the apparent dailymotion of the stars as seen from Chico. This motion is due to Earth's rotation and is the same day afterday, year after year1. We will now focus on two more complicated concepts:1) Apparent daily motion of the stars as seen from the equator and from the North Pole.2) The apparent long-term motion of the sun. The sun displays the same daily apparent motions as thestars do and, in the course of one day, it seems to maintain a fixed position with respect to thestars. However, if we carefully observe the sky for several days, weeks or months (similar to whatyou did as you conducted your moon study), we can detect a motion of the sun relative to thestars.2In the planetarium, we can see what the night sky looks like at distant locations on earth withoutactually having to travel there. We can also make observations very efficiently by speeding up time.Best of all, we can take away the apparent motions that are caused by Earth's rotation. Imagine taking aphotograph of the sky at exactly the same time every night for many nights in a row; if you put thosephotographs together and made a movie, it would be similar to what we can show in the planetarium.The planetarium also gives us the power to make the sun so dim that we can still see the stars duringthe daytime. In summary, using the power of the planetarium, we will not see any apparent dailymotions due to the Earth's spin; we will only see the apparent annual motion of the sun due to theEarth's revolution around it.ObjectivesWhen you have completed this lab you should be able to1. Use the altitude (angle above the horizon) of Polaris to determine your latitude.2. Describe the apparent nightly motion of the stars as seen from the North Pole and from theEquator and explain why the stars seem to move the way they do at these locations.3. Describe the apparent annual motion--i.e. apparent motion due to Earth's revolution--of the sunacross the constellations and explain why it seems to move the way it does.4. Describe the difference between the Ecliptic and the Celestial Equator.5. Discuss the astronomical basis for Astrology (movement of the sun, moon and planets through thesigns of the Zodiac) and why scientists have no faith in Astrology. 1 We will ignore the motion of the stars relative to each other and the effects of the precession (gradual change inorientation) of Earth's axis, both of which happen so slowly that no human being can live long enough to notice.2It is this movement that caught the attention of early astrologers who, perhaps understandably, concluded that it hadprofound spiritual significance.C–42 Planetarium Lab #2: Variations in the Sky With Latitude and SeasonLab Activity #1: Modeling the Apparent Motion of the Sun Through theConstellations of the ZodiacMore Activity: (Do this activity as a whole class) One person represents the earth, another representsthe sun and everyone else represents stars. Form a large circle with the “sun” in thecenter and the “earth” next to the sun. Space the various “stars” unevenly around thecircle. Everyone stays in place except the “earth.” The “earth” will spin and orbitaround the “sun” (be sure to spin and orbit in the proper directions).3Illustration of the Activity(Source: p. 30 of the chapter on Planets in The Universe at Your Fingertips: an Astronomy Activityand Resource Notebook: Astronomical Society of the Pacific, 1995).Lab Activity #2: Watching the Sun Move Through the Constellations of theZodiacActivity: Go into the planetarium. Your instructor will show what you would see if you continuallykept your gaze on the same stars for a year and watched the apparent motion of the sun asEarth circled around it. The path apparently followed by the sun in this demonstration iscalled the ecliptic. 3The earth spins counterclockwise as seen from above the north pole. The earth orbits the sun counterclockwise as seenfrom above the sun's “north pole.”Planetarium Lab #2: Variations in the Sky With Latitude and Season C–43Question: As the sun appears to move with respect to the stars, it passes “through” the twelveconstellations of the Zodiac. What is causing this apparent motion of the sun across theseconstellations? Draw a diagram to illustrate your answer.More Activity: The planetarium (and your “SC001 Constellation Chart”—handed out in class) showsthe ecliptic as a smoothly curving line sweeping across the 12 constellations thatcorrespond to the 12 signs of the Zodiac. Notice the dates inscribed along the ecliptic;each date marks the position of the sun (as seen from Earth) with respect to thebackground stars on that date.Locate your birthday on the ecliptic. Then note the constellation that that location is“in” (or nearest to). Your astrological sun “sign” is supposed to be the constellationthat the sun was “in” on your birthday. Locate the constellation that corresponds tothe sun “sign” you have always considered yourself to be.Questions1. Is the sun actually “in” your supposed sun sign constellation on your birthday? If not, which“sign” is it “in?”2. For those who have done the reading for homework #9, explain why, for most people, the sun isnot in the “proper” constellation on their birthday.C–44 Planetarium Lab #2: Variations in the Sky With Latitude and SeasonLab Activity #3:Why Do We See Different Constellations at Different Times of the Year?Activity: On the ceiling of the planetarium, watch the motion of the stars and the sun as seen fromChico for one 24-hour period (today's date).Questions1. If there were no sun and we could see stars all day and all night, would we be able to see the sameconstellations every day of the year? Explain the reasoning behind your answer.2. If you were to stay up all night tonight and watch the stars, you would not see the constellationsPisces, Cetus or Aries. Similarly, if you would stay up all night in the middle of June, you wouldnot see some of the constellations that you learned earlier this semester--i.e. Orion, Taurus, thePleiades, Canis Major and Gemini. Why are some


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Chico GEOS 142 - Planetarium Lab #2: Variations in the Sky With Latitude & Season

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