Clusters of galaxies are the largest organized structures in the Universe.
They contains 100's of bright galaxies and 1000's of fainter galaxies
in a regions which is several Mpc in size. Although originally defined
as collections of galaxies, the dominant observed form of matter in
clusters is actually diffuse, hot intracluster gas at a temperature of
around 100 million K. This gas contains about 20% of the mass of the
cluster, while the stars and galaxies contain only about 4% of the mass.
Most of the mass is "dark matter" which is only detected gravitationally.
Topic convered will include the physical properties of clusters of galaxies,
the nature of their galactic populations, and the properties of the
hot, X-ray emitting gas. The use of clusters as cosmological probes will
also be described.
