The answer depends on what you mean by "astronomy." If you want a reference for backyard astronomy and/or how to properly set up and use a small telescope, then I recommend The Backyard Astronomer's Guide by Dickinson and Dyer
It is very well written and quite comprehensive.
However, if you're looking for something more formally academic, then it depends even more on what you are looking for. The traditional introductory textbooks used in college and university courses are woefully inadequate, so much so that I don't even use them for the courses I teach any more. Too many publishers are obsessed over details (e.g. current number of jovian satellites, extrasolar planets, etc.) that they leave out the fundamental science, which renders them useless for their intended purpose in the first place. If you really want to see what textbooks used to be, find a very early edition of George Abell's book Exploration of the Universe. The second edition in front of me is copyright 1969. The science foundation is excellent and the level of presentation is much deeper than any contemporary text. The fundamentals never change. Obviously, some here will disagree with me but with twenty years of undergraduate teaching experience I stand by my comments.
This post imported from StackExchange Physics at 2014-03-24 05:08 (UCT), posted by SE-user Joe