An Introduction to Astronomy

altitude amount apparent motion astronomical attraction axis azimuth Barnard body celestial equator celestial sphere circle comets computed conclusion Consequently constellations crosses the meridian density depends determined diameter direction distance doub earth earth's atmosphere earth's equator earth's orbit eastward eccentricity ecliptic energy equal example fact forces gravity heat horizon hour angle Jupiter known latitude law of gravitation laws of motion length Lick Observatory light magnitude Mars mass means measured Mercury meridian meteors miles per second molecules moon moon's move nearly Neptune number of stars oblate observations orbit pendulum perihelion period of rotation phenomena Photographed planetesimals planetoids planets plumb line pole position problem radiation respect revolution revolve right ascension satellites Saturn seen sidereal solar day solar system spectroscope sphere spherical sun's Suppose surface synodical period telescope temperature theory tides tion velocity Venus vernal equinox Yerkes Observatory