This is the third of a series of first steps in science, through the dialogue, question and answer method through which the Old Professor teaches inquiring Bobby some of the facts of science behind the things of everyday life. This book includes more than subjects usually associated with astronomy, -- measuring of time, relation of weight and gravity, measuring distance, importance of glass in lenses, etc. Then he takes Bobby in imagination on a trip to the moon, the sun, the planets; he teaches him primary facts about the constellations and the Milky Way. There is no sugar-coating; the story is straightforward fact, handled in this form. Unprepossessing in appearance, but good content material.