Vertical Structure of an Atmosphere. Hydrodynamics of Atmospheres. Chemistry and Dynamics of Earth's Stratosphere. Planetary Astronomy. Ionospheres. Airglows, Auroras, and Aeronomy. Stability of Planetary Atmospheres. A Table of Physical Constants. Planetary Characteristics. A Model of Earth's Atmosphere. Planetary Spacecraft Missions. Supplementary Reading. The Planck Function. Diffusion Coefficients. Ortho and Para Hydrogen. Partition Functions for a Spherical Exosphere.