Astronomy

They offer an integrated M.Tech + Ph.D program. As mentioned on their website here is the eligibility
'The Integrated M.Tech- Ph.D (Tech.) Programme will admit bright, highly motivated students with a three years B.Tech. degree (Post BSc Hons) in Optics and Optoelectronics / Radio Physics and Electronics from CU or B.Tech / BE degree in Electrical/ Instrumentation/ Electronics and Communications /Computer Science and Engineering from an institution recognized by AICTE. A candidate with M.Sc degree in Physics / Electronic Science / Applied Mathematics /Applied Physics from a UGC recognized institution is also eligible to apply'.
Hence you must hold either of these degrees and pass out with flying colors to be eligible. They will also hold an entrance test. Please check the website of IIAP.

The Indian Institute of Astrophysics is a premier institute devoted to research in astronomy, astrophysics and related physics. Institute runs a full-time research programme where in the students work towards their Ph.D. degree under the supervision of an IIA faculty. Students may join the programme in either the first semester beginning in August or the second semester beginning in January. Entrance examination is held in December followed by interview in January. Students passing the JEST exam are interviewed in May / June. The eligibility criteria for PhD at IIA is M.Sc in mathematics / applied physics / applied mathematics / optics and photonics / instrumentation / electronics, etc. All around excellent academic performance from 12th to PG will help you fulfill your dream.
Indian Institute of Astrophysics also conducts the Integrated M.Tech- Ph.D (Tech.) programme in Astronomical Instrumentation in collaboration with Department of Applied Optics and Photonics, University of Calcutta (CU). The Degree will be awarded by the University of Calcutta. The duration of M.Tech course work will be of 2 years divided into 4 semesters. After successful completion of the M. Tech course a student can opt for registration for Ph.D (Tech.) programme, subjected to a selection procedure and minimum cut-off grade.
The Integrated M.Tech - Ph.D (Tech.) Programme will admit bright, highly motivated students with a three years B.Tech. degree (Post B.Sc Hons) in Optics and Optoelectronics / Radio Physics and Electronics from CU or B.Tech / BE degree in Electrical/ Instrumentation/ Electronics and Communications /Computer Science and Engineering from an institution recognized by AICTE. A candidate with M.Sc degree in physics / electronic science / applied mathematics /applied physics from a UGC recognized institution is also eligible to apply.
You are advised to take PCM subjects in 10+2 board. After that you can take either engineering or science route to fulfill your dream.

You must have physics and mathematics at the plus two level as well as during graduation.
Institutes in India offering astrophysics courses are:
Aligarh Muslim University, Andhra University, Rashtrasant, Tukdoji Maharaj, Nagpur University, Aryabhata Research Institute of Observational Sciences (A.R.I.E.S) Bangalore, Institute of Technology, St. Xavier's College-Cochin, University of Science and Technology, Dr. Babasaheb Ambedkar Marathwada University, Harish Chandra Research Institute, Indian Institute of Astrophysics, Indian Institute of Geomagnetism, Indian Institute of Science (IISC), Indian Institute of Technology, Inter-University Centre for Astronomy and Astrophysics (I.U.C.A.A.), JNTU College of Engineering-Madurai, Kamaraj University, Mahatma Gandhi University, Osmania University, Patiala University, Physical Research Laboratory (PRL)-Punjab University, Raman Research Institute, Gulbarga University, S N Bose National Centre for Basic Sciences, Shivaji University, Swami Raman and Teerth Marathwada University, Tata Institute of Fundamental Research, Tezpur University, Indira Gandhi National Open University, University of Chennai, University of Kolkata and University of Lucknow.