Spectral synthesis code to simulate conditions in interstellar matter
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Most of the quantitative information we have about the cosmos comes from
spectroscopy. In many cases the light we analyze was produced by atoms in
the first generations of stars and galaxies.  The spectra are produced by
dilute gas where such properties as the gas kinetic temperature, chemical
state, level of ionization, and level populations, are determined by a
host of microphysical processes rather than by a single temperature.
Analytical solutions are seldom possible and computer solutions are
needed to understand their physical properties. Numerical simulations make
it possible to understand complex physical environments starting from
first principles. Cloudy is designed to do exactly this.