Hello Jericho Jonah ,

If you wish to become an astronomer in ISRO so you should go ahead with astrophysics....

After completing Msc in physics you could apply for the job in ISRO.

You can work as research associate in various projects in ISRO.

Also Msc Physics graduates can apply for technical posts in ISRO. Generally you will be considered for Research /Scientists/ Senior Physicist positions in ISRO.

It's all up to you .....to decide the perfect side according to your interest

Hope this helps

Thank you !