New books about astronomy, aimed at general readers, are coming out all the time. The most obvious reason for this is that it’s a subject that never stands still, and even a book written five years ago can look dated to anyone who keeps up with the latest theories and discoveries. While authors are scarcely likely to complain about the ongoing demand for new books, they may struggle to find a sufficiently fresh angle to make their latest contribution stand out from its predecessors. Yet that’s what Brian Clegg has done brilliantly well in Interstellar Tours , which presents what might have been a pretty standard account of the make-up of our galaxy from a strikingly different perspective. Clegg asks us to imagine we are 22nd-century tourists taking a short cruise around the galaxy on a starship that’s capable of jumping, more or less instantaneously, to any point within a 100,000-light-year sphere centred on the Earth. This much is science fiction, because there’s no way it could be ma...