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.

By the end of the module the student should:
• Have a firm grasp of the concept of a stable system and how
forces balance in typical astrophysical systems;
• Display a good working knowledge of the principles governing
the behaviour of rotational systems, and the application of the
concept of conservation of angular momentum, in particular in
the context of the dynamics of planetary systems and binary
systems;
• Be familiar with the various methods used to detect exoplanets,
and the strengths and weaknesses of each method dependent
upon the intrinsic and observational properties of exoplanet
systems;
• Be able to apply familiar laws of dynamics to simple spherically
symmetric distributions of matter, and apply them to
understand the dynamical evidence for dark matter in galaxies;
• Be familiar with the Virial equation, and be able to apply it, both
qualitatively and quantitatively, in several astrophysical
contexts;
• Be able to manipulate, and discuss the physical significance of,
equations describing simple Newtonian cosmologies.