AST-1002 Lecture 3: Motion of Earth and the Moon
Document Summary
All stars rise and set due to earth"s motion. If we take out rotation of earth, the stars seem to be fixed. Theyre so far away that any movement goes unnoticed with the naked eye. So the stars are a good fixed reference point. Planets appear to wander with respect to the background fixed stars. Planets mostly go prograde, but sometimes they have an apparent retrograde motion. Everything revolves around us-- we are the center of the universe. When faced with two hypotheses that explain all the observations equally well, go with the one with one that requires the fewest assumptions. Empirical : use prior data to make predictions, but there is no real underlying theory. The size of an ellipse is specified by its semimajor axis, a. The shape of an ellipse is specified by its eccentricity, e. Distance from the center of the ellipse to the focus. Earth"s orbit is only slightly eccentric-- . 016 so very circular.
