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Lecture 4Earth, Moon, Sun System
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Rising and Setting
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Circumpolar Constellations
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Motion of the Sun
Earth goes around the sun once a yearAppears that the sun moves through the skyalong a line called the ecliptic.Sun moves 1 degree eastward per day.Constellations along the ecliptic are the 12constellations of the zodiac
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Motion of Sun along Ecliptic
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Precession of the Earth’s Axis of RotationNorth Celestial Pole moves with a period of26,000 yearsIn Egyptian time Thuban was the North StarIn 12,000 years (14000 A.D.) Vega will be theNorth Star
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Precession
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Precession effect on pole star
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Motion of the Sun
Magnitudes again, 5 in 100. Know what thatmeans!Ecliptic: Path of the sun in the sky. Know thedifferent definitions for the ecliptic.Sun moves 1◦/day
360◦/year365.25day/year
≈ 1◦/day
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Seasons I
When it is summer in Oklahoma, whatseason is it in Chile?
(a) Summer(b) Fall(c) Winter(d) Spring
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Seasons II
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Seasons III
Are Seasons caused by a change in theEarth-Sun Distance?
(a) Yes(b) No
Earth’s Rotation axis tipped 23.5◦ to plane ofeclipticResponsible for the seasons.Planets confined to (nearly) the plane of theecliptic
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Celestial Sphere and Seasons
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Summer Light versus Winter Light
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Summer Solstice
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Winter Solstice
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Sun Position with Season
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Sun Simulation
Sun Simulator
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