An Introduction to Astronomy

altitude appear asteroids astronomers atmosphere average axis bright star brightest calendar celestial bodies celestial equator celestial sphere cepheids circle clouds comet constellations corona craters dark diagram diameter direction disk dust earth earth's orbit east eccentricity eclipse effect fainter galactic system galaxies gases globular clusters Hale telescope heavens hemisphere horizon hour hydrogen inclined Jupiter latitude light lines longitude lunar magnitude main sequence maps Mars mass mean distance meteorites meteors miles a second Milky million miles moon moon's motion Mount Wilson Observatory naked eye nearly nebula northern novae observed Palomar Palomar Observatories parallax perihelion period phases Photographed at Mount radio telescopes reflecting telescope refraction region revolution revolve right ascension rings satellites Saturn seasons sidereal solar south celestial pole spectra spectrum speed spiral sun's sunlight sunspot surface tion umbra variable stars Venus vernal equinox visible wave lengths Yerkes Observatory zenith zodiac