This is an extensive revision of the first (and still, only) introductory astronomy text to take a ``discovery activities'' approach to learning astronomy, encouraging students to be active rather than passive learners. Students use an equipment kit included with the book to construct observing instruments, including a telescope, so they can carry out measurement activities and obtain direct experience in the scientific gathering and analyzing of data. The text is flexible; it is not a lab manual. The equipment kit is available separately; it contains a simple telescope, a cross-staff, quadrant, spectroscope, Ray Box grill, telescope, and diffraction grating. Changes in this new edition include greater adaptability of the text, updated astrophysics, observations from the Voyager mission, discussion of grand unified theories and of the inflationary universe.