A Guide to Wider Horizons
This is a book by an astronomer, but it is not primarily about astronomy.  It also discusses physics, mathematics, biology, statistics, linguistics, ethics, history, economics, and literature.  Its purpose is to introduce the reader to a large number of interesting ideas, and other books to read.  It should appeal to any avid reader who wants to expand his or her horizons.  As a result, it could be used as supplementary reading in any college class for non-science majors.  Even if you only have 5 or 10 spare minutes a day to read (such as on a bus to work), this is a book that can help you connect to many things that are new and interesting.