1. Seasonal Motion

2. The Zodiac throughout the Year
Slow drift across background of fixed stars caused by rotation of earth about sun
Period = 1 year (365 ¼ days)
Example: In Winter sun in Sagittarius, Gemini at night sky; in summer sun in Gemini, Sagittarius at night sky

3. How do we “see” that the earth is moving around the sun or v.v.?
Small discrepancy between sun’s motion and motion of stars
Sidereal vs solar day
At noon, say, the sun is not exactly in front of the same stars on the next day.
It is exactly in the south
The stars are faster, so a little west of south

4. Position of Ecliptic on the Celestial Sphere
Earth axis is tilted w.r.t. ecliptic by 23 ½ degrees
Equivalent: 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
Skyglobe demo
7 visible “planets” incl. the sun and moon
Planet = “wanderer”
Days of the week named after the planets

5. Note: Three Coordinate Systems!
Two rotations about differently oriented axes, plus an observer that is oriented in a third direction!

6. Homework: Starmaps 1& 2, March 1, 2006 & April 1, 2006

7. Homework: Star Maps 3 & 4, March 2, 2006 & March 1, 2007

8. Homework: 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”