How old is the universe? What was the Big Bang? How does space travel work? Find out in this interactive book with 100 questions and answers and 70 flaps to lift. Discover what a planet is, look at the eight planets of the solar system, learn why a year is 365 days long, find out what life is like for astronauts, see the amazing Milky Way and take a closer look at life outside our galaxy ... could aliens really exist?