MISCELLANEOUS WEB SITES

AST 3047

1. Here are some links to pages dealing with the celestial sphere and the apparent motions of the Sun and Moon from Dr. Nick Strobel: (a) daily motion of stars and celestial sphere at different latitudes; (b) apparent motion of the Sun; (c) coordinates including equatorial; and (d) solar and sidereal days and tropical and sidereal years and seasons; (e) Moon's synchronous motion; (f) sidereal and synodic months and Moon's phases, eclipses. I've also thrown in Strobel's version of the inferior and superior planets and retrograde motion.

There are a few minor errors in these. First, at the North Pole all directions are S, which changes a couple of things. Second, at one point it states that the equatorial coordinate system is fixed with respect to the stars, meaning that it doesn't change. That's almost right; just remember that precession does cause a slow change, as it says farther down. Thirdly, the diagram showing the celestial sphere with the ecliptic going up from right to left is backwards -- it should be the other way. (Think about it!) Fourth, the path of the North Celestial Pole with precession is seen looking up, just as in lecture. Lastly, you can ignore the mention of the Moon's perigee in connection with eclipses, and what Strobel refers to as "precession" is what I have called "regression." I think those are all the ones that count.

2. I've found a couple of pages dealing with retrograde motion. For an animation showing what retrograde motion looked like on the sky a few years ago as well as diagrams showing how it worked in the Ptolemaic system and how it works in the modern (Copernican) system click here.