Just a note though--the first edition of ostlie and caroll is probably pretty outdated on certain topics at this point. I used it several years ago and even then there were areas where it wasn't abreast of new developments (this is to be expected considering how much research is continually being done). You'll probably want to get the newest edition or you might end up stuck thinking we've only discovered a dozen or so exoplanets or that Pluto is still a planet!