Hello Abhishek,

To become an astronomer the prefered subjects one should pursue are physics or aeronautics in graduation, masters which would be followed by PhD. Pursuing biology as a subject won't help much.

Good Luck!

Heyyy Abhishek.....

After 12th you'll need to do undergraduate in aeronautical engineering or in physics and then masters in the same for becoming an astronomer. You'll also need to get a doctorate. You can get a good career in  ISRO with different entrance exam's.