f10_sep07 - Ast 307 Ast 307 - Sep. 7, 2010 Sun ’s motion...

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Unformatted text preview: Ast 307 Ast 307 - Sep. 7, 2010 Sun ’s motion and the seasons Phases & cycles of the Moon Eclipses of the Sun and Moon Ast 307 Day and Night are defined in terms of the sun’s location in the sky (direction), which changes over 24 hours as seen from any given point on Earth Where the Sun is in your sky determines your local time of day Ast 307 … and the stars you see at night are those in the (180º) opposite direction Ast 307 What’s wrong with this diagram? Ast 307 Sidereal Day vs. Solar Day A 360° turn points you back in the same absolute direction, according to the stars. Earth has to turn a little farther than that, in order to again directly face the Sun. So the solar day is slightly (4 min) longer than the sidereal (starry) day. Ast 307 Synodic vs. Sidereal Month Ast 307 The constellations you see depend on your latitude and time of year • They depend on latitude because your position on Earth determines which constellations remain below the horizon, cut off by the solid Earth. • They depend on time of year because Earth’s orbit changes the apparent location of the Sun among the stars… and you can’t see stars in the daytime! Annual Motion Ast 307 Ast 307 The ecliptic: a ‘bird’s-eye view • As the Earth orbits the Sun, the Sun appears to move eastward....
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This note was uploaded on 04/30/2011 for the course AST 317 taught by Professor Dinerstein during the Fall '10 term at University of Texas at Austin.

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f10_sep07 - Ast 307 Ast 307 - Sep. 7, 2010 Sun ’s motion...

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