AST 2002 Lecture Notes - Lecture 1: Minute And Second Of Arc, Hyperbola, Tycho Brahe
Document Summary
History of the universe: the cosmic calendar: a scale on which we compress the history of the universe into 1 year. At an average distance of 1 au = 150 million kilometers. With earth"s axis titled by 23. 5 degrees (pointing to polaris) Rotates in the same direction it orbits, counter-clockwise as viewed from above the north pole: out sun moves randomly relative to the other stars in the local solar neighborhood. At typical relative speeds of more than 70,000 kilometers per hour. But stars are so far away that we cannot easily notice their motion and it orbits the galaxy every 230 million years. Earth around the sun, motion of the sun around the center of the milky way. Solstice (december 21st), and spring vernal equinox (march 21st) *counterclockwise cycle: earth"s axis points in the same direction (to polaris) all year round, so its orientation relative to the sun changes as earth orbits the sun.
