Popular Astronomy

angle aperture appear astronomers atmosphere attraction axis bright celestial sphere centre century circle comet constellation Copernican system Copernicus dark described determined diameter direction disk distance diurnal motion earth entirely equal equator equinox eye-piece focus force glass gravitation heat heavenly bodies heavens heliometer Herschel Hipparchus horizon inches instrument Jupiter Kepler known latitude latter lens light lines longitude magnifying power magnitude Mars mass measure Mercury meridian method miles minutes mirror moon moon's move naked eye nearly nebula node object object-glass observations Observatory orbit pass perihelion period photosphere planet pole position prism proper motion Ptolemy rays reflected reflecting telescope refraction result revolution revolving right ascension ring rotation round satellites Saturn seen sidereal solar parallax spectrum spots stars stellar sun's supposed surface tance telescope theory tion total eclipse transit of Venus Uranus vapor velocity visible zenith