The present volume has been prepared With a double purpose, and upon a plan somewhat unusual. First, an effort has been made to meet the Wishes of the ordinary reader who may desire to inform himself as to the present state of astronomic science, or to secure a simple explanation of the many phenomena constantly exhibiting themselves in the universe about him and the further purpose has been to produce a satisfactory textbook for use in high schools and colleges. Thus, for the general reader, it has been thought necessary to eliminate all formal mathematics; for the student, on the other hand, the occasional use of elementary algebra and geometry are essential. To satisfy these two apparently contradictory conditions, the book has been written in two parts; the first free from mathematics, the second a series of extended elementary mathematical notes and explanations to which appropriate references are made in the first part of the book. Thus the general reader may confine his attention to the non-mathematical part; the student should master the Whole volume.