Astronomical Essays Historical and Descriptive

4th magnitude Al-Sufi Algol ancient apparent diameter Arabians Arabic name Arcturus Argelander astronomers binary star bright star brighter called catalogue celestial centre century B.C. Chinese components constellations Cygni dark body density distance of Sirius double stars earth eclipses equal estimate faint stars fainter fixed stars Flamsteed globular clusters Greek Harvard heavens Herschel thought Hipparchus Houzeau hypothesis Jupiter known Leonis light luminosity lunar magni magnitude by Ptolemy measures Messier Messier 67 Milky millions modern moon moon's naked eye nebulæ nebulosity nebulous matter number of stars observations Observatory Ophiuchi orbit Orion parallax period photographs photometric planets probably Procyon Professor proper motion Ptolemy Ptolemy and Al-Sufi Ptolemy's reference remarkable ring satellite Saturn seems sidereal Sirian type Sirius small stars solar spectroscopic spectroscopic binary spectrum spheres stellar stellar magnitude sun's mass supposed surface luminosity Tauri telescope theory tion tude Tycho Brahé variable stars velocity