Edexcel recomends a physics GCSE instead. Although it probably won't have the same level of content as a GCSE dedicated to Astronomy.
There is an Astrophysics module in Physics A Level that seems to go into the subject in more detail.
So if you're going to take it you NEED to in the next two years as it will no longer exist after that.
It's a fun GCSE and not too taxing.
Most useful when you are applying to a sixth form or university as they are always looking for grades.
There is coursework, however, there is not a lot.
I imagine your school would not be offering this (whoever is reading) but there are many websites which help you through the course like these:
You will have to do a lot of the learning alone so you'll need books, probably these:
I'm not sure if i'm going to do it myself so yeah have fun.