60 THE UNIVERSE A VAST SYSTEM OF PARTS 20. After the completion of a study of this unit on astronomy, a student wrote, " I was very much interested in this study of astrology." Write a paragraph using this statement as your text. 21. What are the major ideas of astrology? 22. Differentiate between astronomy and astrology. 23. Look up the meaning of the word astronomy in an encyclopedia. 24. State Kepler's three laws of motion.
UNIT II SECTION 2 TELESCOPES HAVE GREATLY EXPANDED MAN'S CONCEPTION OF THE MATERIAL UNIVERSE Like buried treasures, the outposts of the universe have beckoned to the adventurous from immemorial times. Princes and potentates, poHtical or industrial, equally with men of science, have felt the lure of the uncharted seas of space, and through their provision of instrumental means the sphere of exploration has rapidly widened.^ — George Ellery Hale. Introduction. Galileo's application of the telescope to astronomy was very significant because it extended the observational basis for generalizations in the telescope. concerning the heavenly bodies. It revealed an unknown universe, whose vast proportions have been expanded with each improvement This section deals with the development of the telescope and the information thus made available. Telescopes Have Been Greatly Improved Since the Time of Galileo. Galileo's telescope was a refracting type, based on the extremely simple, familiar principle that a convex lens will bring light to a focus by bending (refracting) it. There are two lenses in a refracting telescope — one, the object glass, brings the light to a focus; the other, the Piece Fig. 3. The principle of the refracting telescope. eyepiece, magnifies the image. The focal length of the magnifier, or eyepiece, in relation to the focal length of the objective, determines the magnifying power of the telescope, and the amount of magnification may be changed by merely changing the eyepiece. The telescope concentrates the light which is too faint to be visible ' Signals from the Stars, Charles Scribner's Sons, New York. 1931. 61