I. The tools of astronomy -- The celestial sphere -- Celestial mechanics -- The continuous spectrum of light -- The theory of special relativity -- The interaction of light and matter -- Telescopes -- II. The nature of stars -- Binary stars and stellar parameters -- The classification of stellar spectra -- Stellar atmospheres -- The interiors of stars -- The sun -- The interstellar medium and star formation -- Main sequence and post-main-sequence stellar evolution -- Stellar pulsation -- The fate of massive stars -- The degenerate remnants of stars -- General relativity and black holes -- Close binary star systems -- III. The solar system -- Physical processes in the solar system -- The terrestrial planets -- The realms of the giant planets -- Minor bodies of the solar system -- Formation of planetary systems -- IV. Galaxies and the universe -- The Milky Way galaxy -- The nature of galaxies -- Galactic evolution -- The structure of the universe -- Active galaxies -- Cosmology -- The early universe -- Appendixes: -- A. Astronomical and physical constants -- B. Unit conversions -- C. Solar system data -- D. The constellations -- E. The brightest stars -- F. The nearest stares -- G. Stellar data -- H. The Messier catalog -- I. Constants, a programming module -- J. Orbit, a planetary orbit code -- K. TwoStars, a binary star code -- L. StatStar, a stellar structure code -- M. Galaxy, a tidal interaction code -- N. WMAP data.