Dear Vishnu, To start a career in Astronomy, you should take up Mathematics, Physics and Chemistry after your 10th. You should complete your 10+2 in these subjects with a minimum aggregate of 50%. You need to pursue your Bachelor's in any one subject among Physics/Mathematics and score a minimum aggregate of 50%.  You can also pursue B.Tech and then take up Masters in Astrophysics. But to be relevant, B.Sc in Mathematics or Physics is advisable. In Masters you can choose Astrophysics/Astronomy. There are full time Ph.D programmes in Astrophysics /Astronomy. For that you need to complete your Masters, qualify in the valid Entrance exam and then clear the Personal Interview.