This newly revised and updated Ninth Edition of HORIZONS shows students their place in the universe ? not just their location, but also their role as planet dwellers in an evolving universe. Fascinating and engaging, the book illustrates how science works, and how scientists depend on evidence to test hypotheses. Students will learn to focus on the scientific method through the strong central questioning themes of "What are we?" and "How do we know?" Students are also provided with an assessment tool, AceAstronomy, to help test their knowledge of the concepts through assessment, tutorials, and post-tests.