The Universe is full of structure. Most of the matter we can see is gathered into large, hot spheres, accompanied in most cases by planetary systems. The stars are grouped into galaxies, and these in turn are distributed in a network of clusters and filaments. In this lecture module, we will survey the properties of astrophysical structures and try to understand them in terms of the physics at play. We shall pay particular attention to the importance of rotation, and angular momentum, in systems, e.g., the orbital motions in galaxies and planetary systems. In this context, we will examine the evidence for dark matter in galaxies, and explore in detail the various methods now being used to find extra-solar planets. Finally, we will apply the principles of Newtonian dynamics to examine the expanding Universe, to address basic cosmological questions like how old the Universe is and how fast it is expanding. |