Astronomy is basically about observing the motions of heavenly bodies in the sky and their patterns, while cosmology is the study of the history and structure of the cosmos, or the universe, as a whole. To get into these fields, you need to study physics, maths or engineering at the undergraduate level and then take up the relevant study programme for your masters or doctorate.
There are no BSc programmes in cosmology but there are masters-level research programmes which cover cosmology. These include those offered by the Indian Institute of Astrophysics, Bangalore; Tata Institute of Fundamental Research, Pune; Raman Research Institute, Bangalore and the Physical Research laboratory, Ahmcdabad. In addition, the Indian Institute of Science, Bangalore (www.iisc.ernet.in), now offers an integrated BSc/ MSc programme in different fields of science.
The programme is a balanced blend of core science and interdis- ciplinary topics. Do check the details of this programme as it may cover the areas you wish to take up.