Book excerpt: The attempt to understand the universe's seemingly endless mysteries involves a process of discovery that can evoke fascination, frustration, and continual wonder and amazement. Planets, Stars, and Galaxies, Third Edition takes readers on an incredible full-color journey through the vast universe. This engaging title tackles the questions students studying science are eager to know: How large is the universe? Is it infinite or finite? What is its structure? Is it possible to visit other worlds, and if so, what similarities might they bear to our own world?