iOS Pick: Universal Zoom
Leo Laporte's app cap on iOS Today 287 is Universal Zoom by GamifyIt. This is an educational app that's all about scale, sizes, and distances. You can just zoom in and out to discover the relative sizes of animals and objects. You can also compare any two objects.
Universal Zoom makes it fun to discover really small things like subatomic particles all the way up to very large things like planets and galaxies and everything in between. The app features great graphics and intuitive navigation. It also includes Wikipedia access to read more about the things you discover.