ILLUSTRATIONS IN THE TEXT THE RATIONAL AND THE SENSIBLE 12 HORIZON ALTITUDE AND AZIMUTH 14 RIGHT ASCENSION AND 35 DECLINATION THE ECLIPTIC AND CELESTIAL 51 LATITUDE AND LONGITUDE HOW THE EARTH CONTROLS THE 75 MOON THE TIDAL FORCE OF THE MOON 79 REFRACTION 85 DIP OF THE HORIZON 87 SIDEREAL AND SOLAR TIME 93 THE CHANGE OF DAY 101 THE SEASONS 107 PARALLAX OF THE MOON 139 PARALLAX OF THE SUN FROM 141 TRANSIT OF VENUS SPECTRUM ANALYSIS 147 THE PHASES OF THE MOON 160 ORBITS OF MARS AND THE EARTH 183 ELLIPSE, PARABOLA, AND 203 HYPERBOLA THE NORTH CIRCUMPOLAR STARS 244 KEY TO NORTH CIRCUMPOLAR STARS 245 ------------------------------------------------------------------------ PART I. THE CELESTIAL SPHERE. ------------------------------------------------------------------------ PART I. THE CELESTIAL SPHERE. =1. Definition of Astronomy.= Astronomy has to do with the earth, sun, moon, planets, comets, meteors, stars, and nebulæ; in other words, with the universe, or “the aggregate of existing things.” It is the most ancient of all sciences. The derivation of the name from two Greek words, _aster_, “star,” and _nomos_, “law,” indicates its nature. It deals with the _law of the stars_—the word “star” being understood, in its widest signification, as including every heavenly body of whatever kind. The earth itself is such a body. Since we happen to live on the earth, it becomes our standpoint in space, from which we look out at the others. But, if we lived on some other planet, we would see the earth as a distant body in the sky, just as we now see Jupiter or Mars.