Lecture 6: Daily and Annual Motions

Why do celestial objects appear to rise in the East and set in the West? How does this depend on where you are on the Earth, or the time of year? Today we set the heavens into motion, and look at the two most basic types of celestial motions. Apparent daily motions are a reflection of the daily rotation of the Earth about its axis. The apparent annual motions are a reflection of the Earth's orbit around the Sun. To describe the Sun's apparent annual motion, we introduce the Ecliptic, the Obliquity of the Ecliptic, and four special locations along the Ecliptic: the Solstices and Equinoxes. This will set the stage for much of our discussions in rest of this section. Recorded 2006 Sep 27 in 100 Stillman Hall on the Columbus campus of The Ohio State University.