The World of Comets

according action already amongst ancients apparition appeared astronomers atmosphere become bodies bright brilliant calculated called cause celestial centre century changes comet cometary compared considered continuous course curve described determined diameter direction discovered distance drawing earth eccentricity effect elements elliptic equal explain fact force further give given greater head heavens idea inclination increase influence July June Jupiter kind known least length less light luminous March mass matter mean mention meteors miles motion move movement nature nearly nebulosity node November nucleus observed October orbit origin parabolic passed perihelion perihelion passage period perturbations phenomena physical planets portion position prediction present probable question rays reason regarded region remarkable respect seen situated solar space spectrum stars supposed tail telescope theory true visible