---
author:
- |
    G. J. Ferland, R. L. Porter, P. A. M. van Hoof, R. J. R. Williams, N. P. Abel,\
    M. L. Lykins, Gargi Shaw, W. J. Henney, P. C. Stancil
bibliography:
- 'LocalBibliography.bib'
- './common/bibliography2.bib'
title: The 2013 Release of Cloudy
---

=1

Introduction
============

Most quantitative information we have about the cosmos comes from spectroscopy. In many astronomical environments the density is too low for equilibrium thermodynamics to apply, so the ionization, molecular state, level populations, kinetic temperature, and the resulting spectrum are the result of a host of microphysical processes. As a result the spectrum reveals much about the properties of an object, but it also means that modeling this detail is complex. Analytical results are only possible in certain limits, so numerical simulations must be used. Texts that review this field include @Spitzer1978, @DopitaSutherland03, @Tielens2005, @AGN3 (hereafter AGN3), and @Draine.B11Physics-of-the-Interstellar-and-Intergalactic-Medium.

[^1] is an open source plasma simulation code that is designed to simulate conditions in a non-equilibrium gas, and predict its spectrum. The code incorporates physical processes from first principles, as much as possible. The goal is to simulate the ionization, level populations, molecular state, and thermal state, over all extremes of density and 