The collins dictionary of astronomy is good resource for space/astronomy and there are still some pretty cheap paperback copies around. beware of other dictionaries of astronomy which are full of pretty photographs but not really very useful tbh.
*probably* a GCSE astronomy book, there's one by Patrick Moore and Chris Lintott (which tbh I haven't read - but Moore is usually good at explaining things)
QED by Richard Feinman is readable by an intelligent person and has the scary maths stuff swept out of view.
My old favourite A level physics book (from the days before the exam boards entered into a racket with the book publishers)
Advanced Physics - Tom Duncan. still seems like you can get a second hand copy... but check your exam spec before relying on it totally cos it might not cover everything in the spec.