AstroInfo: Table of Contents The Sky and Coordinate Systems Celestial Coordinate Systems Celestial Equator Celestial Poles Celestial Sphere The Ecliptic The Equinoxes Geographic Coordinates Great Circles The Horizon Hour Angle Local Meridian Precession The Zenith Time Epoch Julian Day Leap Years Sidereal Time Time Zones Universal Time Instrumentation Telescopes Physics Blackbody Radiation Dark Matter Flux Luminosity Parallax Retrograde Motion Astrophysics Elliptical Galaxies Spiral Galaxies The Magnitude Scale Stars: An Introductory &FAQ; Star Colors and Temperatures The Cosmic Distance Ladder