Physical processes which affect interstellar gas will be discussed, including
line excitation, absorption line formation, ionization, heating and cooling,
thermal equilibrium, and thermal instability.
Particular attention will be given to photoionized gas.
The dynamics and distribution of the interstellar gas will also be described.
Hot gas in elliptical galaxies, clusters of galaxies, and the intergalactic
medium may also be discussed.
The optical and physical properties of dust grains will be explored.
There may be some discussion of cosmic rays and interstellar magnetic fields.
