Heyy,
I do GCSE astronomy and I'm actually sitting paper 1 for the GCSE tomorrow! I took Sunday morning classes at the Royal Observatory Greenwich which was cool because we got to watch live planetarium shows on a few of the topics we were learning. Having astronomy as part of your school timetable will be less time-consuming and advantageous in the sense that you'll likely have access to your teacher throughout the week. Mine was not a full-time worker at the observatory so we could only speak to him during our once-a-week lessons and he wouldn't even respond to emails loll. Either way, it's not necessarily a problem as (despite it being a rare option for GCSEs) the many online resources can help guide you through the course - I'll link them below. That brings me to the subject of difficulty. In my opinion, astronomy isn't crazy difficult or hard to understand. I find it quite interesting. Plus, if you don't get something you can simply research it. It's also worth noting that the grade boundaries in this subject are relatively low- I'm pretty sure last year you could get a grade 6 with just over half marks. No one would bat an eye if you didn't do as well in astronomy as the other 12 GCSEs (?!) you're sitting. The whole point of astronomy as a GCSE is that you will be credited regardless since you did more than what the average UK student did. Aiming high is always great but don't let the idea of GCSEs and grades stop you if it's something you want to learn.
BUT
I would not recommend doing Astronomy if:
1) you've looked over the content and decided it doesn't interest you at all (no point doing something you don't care about!)
2) there are more enjoyable or beneficial things you could be doing with your time (you already have a lot going for you academically so instead of sitting another GCSE, consider ways you can branch out: you could take an online course in an area your interested in to help boost your employability, do some work experience, volunteer somewhere, try out a few extra-curricular activities or a new hobby, you could even use the time for some extra rest and relaxation)
3) you will be starting the course in year 11 and sitting the GCSE that same year (maybe I'm biased because I'm a year 10 who started the course in Sep'23 and am sitting the GCSE in June'24, but year 10 really is the best year to do it as there's less pressure from the other subjects at that time. if you're entering year 11 it's much better to focus on the things you already have on your plate.)
4) you are sitting the GCSE in year 10 but have other early entry subjects (you will still be expected to attend classes, complete homework and revise for exams in other subjects while you revise for actual GCSEs, plus there are two mandatory pieces of coursework for astronomy. if you're anything like me your attendance may drop- I frequently have to take days off school to revise, complete unfinished tasks, stay sane etc. I didn't go to school today for all the reasons listed above!)
Those are just my personal takes so consider them but don't let them stop you if it's something you really want to do!! Good luck

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GCSE astronomy links:
Abingdon Science PartnershipNewton's Notepad Space FMPhysics with KeithGCSE Astronomy HelpStudy OnionLawrence SmallmanSpecification (I've assumed your exam board is Edexcel)
Textbook (most learning centres provide this for free but just in case!)
Hope this helps

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