It gives me pleasure to acknowledge that the experience acquired in making the astronomical drawings published in Volume VIII. of the Annals of the Harvard College Observatory, while I was connected with that institution, has been of considerable assistance to me in preparing this work; although no drawings made while I was so connected have been used for this series. E. L. TROUVELOT. _Cambridge, March, 1882._ CONTENTS INTRODUCTION LIST OF PLATES _THE SUN_ GENERAL REMARKS ON THE SUN SUN-SPOTS AND VEILED SPOTS SOLAR PROTUBERANCES TOTAL ECLIPSE OF THE SUN _THE AURORAL AND ZODIACAL LIGHTS_ THE AURORA BOREALIS THE ZODIACAL LIGHT _THE MOON_ THE MOON ECLIPSES OF THE MOON _THE PLANETS_ THE PLANETS THE PLANET MARS THE PLANET JUPITER THE PLANET SATURN _COMETS AND METEORS_ COMETS SHOOTING-STARS AND METEORS _THE STELLAR SYSTEMS_ THE MILKY-WAY OR GALAXY THE STAR-CLUSTERS THE NEBULÆ APPENDIX LIST OF PLATES[1] PLATE I. GROUP OF SUN-SPOTS AND VEILED SPOTS. _Observed June 17, 1875, at 7 h. 30m. A. M._ II. SOLAR PROTUBERANCES. _Observed May 5, 1873, at 9h. 40m. A. M._ III. TOTAL ECLIPSE OF THE SUN. _Observed July 29, 1878, at Creston, Wyoming Territory._ IV. AURORA BOREALIS. _As observed March 1, 1872, at 9h. 25m. P. M._ V. THE ZODIACAL LIGHT. _Observed February 20, 1876._ VI. MARE HUMORUM. _From a study made in 1875._ VII. PARTIAL ECLIPSE OF THE MOON. _Observed October 24, 1874._ VIII. THE PLANET MARS. _Observed September 3, 1877, at 11h. 55m. P. M._ IX. THE PLANET JUPITER. _Observed November 1, 1880, at 9h. 30m. P. M._ X. THE PLANET SATURN. _Observed November 30, 1874, at 5th. 50m. P. M._ XI. THE GREAT COMET OF 1881. _Observed on the night of June 25-26, at 1h. 30m. A. M._ XII. THE NOVEMBER METEORS. _As observed between midnight and 3 o'clock A. M., on the night of November 13-14, 1868._ XIII. PART OF THE MILKY-WAY. _From a study made during the years 1874, 1875 and 1876._ XIV. STAR-CLUSTER IN HERCULES. _From a study made in June, 1877._ XV. THE GREAT NEBULA IN ORION. _From a study made in the years 1873-76._ [Footnote 1: For Key to the Plates, see Appendix.] _Reproduced from the Original Drawings, by Armstrong & Company, Riverside Press, Cambridge, Mass._ GENERAL REMARKS ON THE SUN The Sun, the centre of the system which bears its name, is a self-luminous sphere, constantly radiating heat and light. Its apparent diameter, as seen at its mean from the Earth, subtends an angle of 32', or a little over half a degree. A dime, placed about six feet from the eye, would appear of the same proportions, and cover the Sun's disk, if projected upon it. That the diameter of the Sun does not appear larger, is due to the great distance which separates us from that body. Its distance from the Earth is no less than 92,000,000 miles. To bridge this immense gap, would require 11,623 globes like the Earth, placed side by side, like beads on a string.