  Coronae exist in most astrophysical objects: stars, accretion disks, and
individual galaxies and clusters of galaxies. Coronae in these varied systems
have some common properties: 1) hydrostatic equilibrium in background gravity
is a good assumption; 2) they are optically thin, i.e., photons escape as soon
as they are born; 3) they have cooling times shorter than their ages, and thus
require heating for sustenance. Generally the coronal heating mechanisms are
quite complex but the structure of the corona is tightly constrained by the
interplay of cooling, {\em global} heating, and background gravity. We briefly
summarize the results from our studies of the intracluster medium (the cluster
corona) and draw inferences which should apply to most astrophysical coronae.
