So I've been told recently, that I will be participating in the "British Olympiad in Astronomy and Astrophysics Competition", which I am really excited about. I took the British Physics Olympiad Paper earlier this year, and feel like I could've done better. So because I am quite new to Astronomy and Astrophysics, I would like to study both topics, to see what they are all about. I've been wanting to do this for quite some time now, and think this is the right time to ask: I am wondering if there are any good books/ online guides/ or other material (for free..) which would help me learn more about these broad topics. Keep in mind that i am currently in 9th Grade, so I would prefer a book/resource which material isn't too high above my skill/knowledge level ,However I am always open to more 'advanced' books/resources and will consider these, so please do mention them. Also, are there any other things(e.g. Mathematics) I would have to read up on? Any other tips/suggestions are welcomed. Thanks in advance.