XXXI. Some Astronomical Facts Worth Remembering 250 ILLUSTRATIONS PAGE Northern Portion of the Moon at Last Quarter _Frontispiece_ The Great Hercules Cluster--A Universe of Suns _facing page_ 56 A Dark Nebula: The Dark Bay or Dark Horse Nebula in Orion _facing page_ 110 A. Venus. B. Mars. C. Jupiter. D. Saturn _facing page_ 122 Spiral Nebula in Canes Venatici _facing page_ 216 Spiral Nebula in Andromeda Viewed Edgewise _facing page_ 222 LIST OF TABLES PAGE I. The Principal Elements of the Solar System 261 II. The Satellites of the Solar System 262 III. The Twenty Brightest Stars in the Heavens 263 IV. A List of the Principal Constellations 264-265 V. Pronunciations and Meanings of Names of Stars and Constellations 266-267 PREFACE Astronomy, it has been said, is the oldest and the noblest of the sciences. Yet it is one of the few sciences for which most present-day educators seem to find little, if any, room in their curriculum of study for the young, in spite of its high cultural value. It is, we are told, too abstruse a subject for the youthful student. This is doubtless true of theoretical or mathematical astronomy and the practical astronomy of the navigator, surveyor and engineer, but it is not true of general, descriptive astronomy. There are many different aspects of this many-sided science, and some of the simplest and grandest truths of astronomy can be grasped by the intelligent child of twelve or fourteen years of age. Merely as a branch of nature study the child should have some knowledge of the sun, moon, stars and planets, their motions and their physical features, for they are as truly a part of nature as are the birds, trees and flowers, and the man, woman or child who goes forth beneath the star-lit heavens at night absolutely blind to the wonders and beauties of the universe of which he is a part, loses as much as the one who walks through field or forest with no thought of the beauties of nature that surround him. The astronomer is the pioneer and explorer of today in realms unknown just as the pioneers and explorers of several centuries ago were to some extent astronomers as they sailed unknown seas and traversed unexplored regions. As the years pass by the astronomer extends more and more his explorations of the universe and brings back among the fruits of discovery measures of giant suns and estimates of the form and extent of the universe, views of whirling, seething nebulæ, mysterious dark clouds drifting through space, tremendous solar upheavals or glimpses of strangely marked surfaces of nearby planets.