Structure of OMC-1. (a) The Orion A star-forming cloud seen by Herschel with dust thermal emission. The black rectangle outlines the observed region of OMC-1, centered on the Trapezium star cluster. The image is a composite of 70 μm (blue), 160 μm (green) and 250 μm (red) emission. It spans about 1.3 × 1.6 deg². The moon is shown for scale. (b) OMC-1 composite image covering ~85 arcmin² at ~12″ with three emission lines: the [CII] 158 μm line which traces the FUV-illuminated surface of the molecular cloud (red), the C¹⁸O, J = 2→1 line which traces cold dense gas (blue) and the HCO⁺ J = 3→2 line (green). Reconstruction results will be detailed for positions 1 to 4. Adapted from Goicoechea et al. (2019).