Popular Astronomy

ancient angle apparent motions astronomers atmosphere attraction axis cause celestial equator celestial motions celestial sphere centre century circle comet Copernican system Copernicus dark described determined diameter direction disk distance diurnal motion earth eccentricity entirely epicycle equal equator equinox exact eye-piece focus force glass gravitation heavenly bodies heavens Hipparchus horizon inches instrument Jupiter Kepler known latitude latter length light lines longitude lunar magnifying power Mars mass measuring Mercury meridian method miles minutes mirror moon's move nearly Newton night node object observations Observatory opposite orbit parallax pass perihelion photosphere planet planetary pole position Ptolemaic system Ptolemy rays reflecting telescope refraction result revolution revolving right ascension rotation round the sun satellites Saturn seen shadow side solar spectrum sun and moon sun's supposed surface telescope theory tion total eclipse transit transit of Venus Uranus velocity Venus visible