This module introduces students to the basic principles of theoretical and observational astrophysics. Our current knowledge of our position in our galaxy and the Universe is reviewed. Problems of observing from the Earth and from Space are outlined, and the basic concepts of positional astronomy and the magnitude scale are introduced. Elementary concepts of physics learnt elsewhere are applied to understand the relation between colours of stars, their age and temperature, the evolution of stars throughout their lifetime and the generation of energy in them. The Milky Way is studied in comparison to other galaxies, and the principles of extragalactic study, including measuring distances to them, are introduced. We also review the current understanding of the Hot Big Bang and the subsequent evolution of the Universe, and the evidence that the latter is predominantly made up of dark matter.