The approximate boundaries of the Orion OB associations Ib and Ic are indicated by dashed ellipses. The Orion Id association is directly associated with the molecular cloud behind the Orion nebula, M42. The reddish glow is due to the Hα line, which originates from recombinations in the ionized gas of Barnard’s loop. The belt stars and the knees are obvious. The size of the image is approximately 10° on the sky.