I have cleared INAO twice.

The first time it was junior, so not much competition and I got in without Astronomy stuff.

The OCSC teaches a hell lot of Astronomy. I didn't get into the team in 9th.

I gave in 12 again and cleared without studying Astronomy as I had knowledge from the Junior Camp and strong Physics and Maths(I guess I scored 87/100 or so). Didn't go for the camp though.

Still, you might wanna know about important stars and constellation(frequently asked in INAO). You can use Wikipedia to know about basic Astronomy. Try Schaum’ s( hope I spelt it right) or Roy and Clarke( not recommended before OCSC).

Try online resources and solve past papers thoroughly.

Hope it helps. All the best!!!

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