The structure of the Orion nebula

The Orion nebula is the best studied of all H II regions. The experimental data for this nebula are reviewed, and interpretive models of the structure of both the nebula and its environs are developed. The H II region is composed of an inner 3-min core surrounding the exciting star theta 1 C which is partially imbedded on the near side of a massive neutral complex. A network of strong flows results that resupplies high-density ionized gas to the core region. Gas in the core then freely expands, where possible, primarily into the foreground, south, and west. Details of this model are compared with optical, radio, and infrared observations of the ionized, neutral atomic, and molecular gas in the Orion nebula. The nature of the neutral complex is also discussed.