Hello

First of all, eligibility for MSc Astronomy is that the candidate must have completed +2 examinations with science stream and take Physics as the main subject in his/her undergraduate degree.

MSc Astronomy will include subjects like quantum mechanics, Celestial and Fluid Mechanics, Electromagnetics waves, Electronics, etc., mostly related to physics only. Chemistry will not  a use at all, so go for BSc Physics Honors.

All the Best!