Don’t take math over the summer. While getting ahead may seem like a good idea, colleges (especially selective ones like you mentioned) would much rather you take a full course over the year because then you can actually focus on learning. It would be much better to do some productive EC/internship over the summer. I agree with the others about not retaking physics as well. If you are going to take AP Physics, take it immediately after your current physics class, you will forget material over a year. Also, is it Physics 1, 2, or C? If it is 1 then it may not be the best option because it will be a repeat of the course you are taking (Physics 1 is an introductory course for someone who hasn’t taken physics), it may be better to take AP Bio or AP Chem because they generally aren’t intro courses. If it’s Physics 2 or Physics C (hopefully C) then you should definitely take it if you want to do astronomy.