A compendious and stunningly illustrated fact-filled book for children who have endless questions about how the world works. How do scientists see into space? How do polar bears keep warm? How do keys open locks? How do fireworks explode? Featuring more than 150 compelling questions about space, Earth, machines, buildings, animals, and the human body, this magnificent book by the author-and-illustrator team behind the bestselling First Big Book of Why provides answers for every inquisitive child (and their grown-ups!). And these are answers you can trust, as they have all been thoroughly fact-checked and reviewed by subject experts, who are proudly profiled in the book. With stunning photography and gorgeous original illustrations by Kae Slater, including a host of helpful and friendly diagrams, this is the ultimate gift for kids who need to know everything-- and now!