This colloquium focuses on some (apparently) simple aspects of galaxy formation. The talk includes theory, observation, and simulation, and is aimed at a general astrophysics audience. The starting point is a description of galaxies in terms of their most basic physical properties: mass, scale radius, and rotation velocity, or equivalently, mass, gravitational energy, and angular momentum. This description and some simple theory leads to a physical explanation for the formation of galaxies of different morphological types (aka the Hubble Sequence). Some other highlights of the colloquium are the following: (1) The morphologies of galaxies are closely related to their specific angular momenta. (2) Disk-dominated galaxies have about the same specific angular momenta as their dark-matter halos; spheroid-dominated galaxies have about five times less. (3) Feedback by young stars (galactic winds) and active galactic nuclei is crucial for understanding the angular momenta of galaxies and hence their morphologies and hence the Hubble sequence. (4) The relations between the specific angular momenta and sizes of galaxies and their halos are nearly constant over the redshift range 0 < z < 3. Galaxies and their halos grow together nearly homologously.
Followed by wine and cheese in Pupin 1332.