Example In Winter sun in Sagittarius Gemini at night sky in summer sun in Gemini Sagittarius at night sky How do we see that the earth is moving around the sun or vv Small discrepancy between suns motion and motion of stars ID: 760025
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Slide1
Seasonal Motion
Slide2The Zodiac throughout the Year
Example: In Winter sun in Sagittarius, Gemini at night sky; in summer sun in Gemini, Sagittarius at night sky
Slide3How do we “see” that the earth is moving around the sun or v.v.?
Small discrepancy between sun’s motion and motion of starsSidereal vs solar dayAt noon, say, the sun is not exactly in front of the same stars on the next day. It is exactly in the southThe stars are faster, so a little west of south
Slide4Position of Ecliptic on the Celestial Sphere
Earth axis is tilted w.r.t. ecliptic by 23 ½ degreesEquivalent: ecliptic is tilted by 23 ½ degrees w.r.t. equator! Sun appears to be sometime above (e.g. summer solstice), sometimes below, and sometimes on the celestial equator
Slide5Note: Three Coordinate Systems!
Two rotations about differently oriented axes, plus an observer that is oriented in a third direction!
Slide6Homework: Starmaps 1& 2, March 1, 2006 & April 1, 2006
Slide7Homework: Star Maps 3 & 4, March 2, 2006 & March 1, 2007
Slide8Homework: Use Proportions
Angle traveled compared to full 360 degrees = time elapsed while traveling the angle compared to total time to complete a 360 degree, full rotation
angle/360 = time elapsed / x
x is the period we are looking for, will come out in same units as we put in “time elapsed”