Dear Piyush, You haven't mentioned the University or the State from which you want to pursue your Masters in Astrophysics. However, this is consolidated information regarding a few of the best Institutions offering M.Sc Astrophysics. 

Osmania University, Andhra University and Punjabi University are the best among the Institutions that offer 2-year Full-time Programme in M.Sc Astrophysics. The candidates who wish to pursue this course should have at least score a minimum of 50% in their graduation in Physics. The admission to this course in these Institutions is through entrance examination of these particular universities.

For Osmania University, the entrance examination is OUCET and the application form is available in its official website when the registration opens tentatively from the Month of April. For more information, visit their official website at http://www.osmania.ac.in.

For Andhra University, the entrance examination is AUCET and the application form is available in its official website when the registration opens tentatively from the Month of April. For more information, visit their official website.

For Punjabi University, the admissions are based on Merit in your graduation. For more information, please visit their official website. 

Almost all the Universities begin their admission process by April and close it by June/July.

If you have any University that you want to know about in particular, please do let us know so that we can consolidate that information for you.