Interior screen from 'Stephen Hawking's Snapshots of the Universe" (Random) Hawking

While still not a household word, since the November 2014 release of film The Theory of Everything, the name Stephen Hawking is known to many. Through text and activities, today's app explains some of the science behind the British physicist's work. Gretchen Kolderup reviews the production below. Move planets into place and launch them into orbit, tilt the iPad to reposition a space ship, and zoom in to discover black holes as Stephen Hawking’s Snapshots of the Universe (Random, iOS, $4.99; Gr 5 Up) guides you through our understanding of the universe. Interactive experiments demonstrate the relativity of time, gravity as a bending of the space-time continuum, black holes, and more. The smooth integration of the accompanying text and occasional video segments address the underlying science. From the "Atom of Democritus" to the contemporary "No-Boundry Proposal" various models of the universe are briefly explained. Clean, colorful visuals, subtle musical cues and sound effects, and an intuitive interface make this app friendly and also accessible to younger users, who may enjoy the experiments (such as dropping watermelons from the Tower of Pisa) even if they're not ready for the scientific explanations. Teachers will appreciate the opportunity for students to explore a concept before going deeper—but they will need to go deeper elsewhere; despite physics being fundamentally mathematical, none of the relevant equations are mentioned here. An additional pack containing two experiments can be purchased in-app for a minimal fee, and each text explanation ends with an invitation to learn more by buying one of Hawking's books. Users are also given the option to "share" via email or social networks (just posting a link to the app, not actual content or any personal information). While the replay value may not be very high—it's easy to blast through the experiments and explanations in one sitting—this app is a delight to use and makes for a fun introduction to big concepts in astronomy.—Gretchen Kolderup, New York (NY) Public Library For additional app reviews, visit the Touch and Go webpage.