With a diameter of 36° the Gum nebula (named after the Australian astronomer Colin Gum) is one of the largest Hα emission regions in the sky. It is located in the southern constellations of Puppis and Vela. Relatively little is known about the origin of this object, although it is thought to be the remnant of a supernova explosion one million years ago. The Vela Supernova Remnant appears to be embedded in this nebula, although the two are considered separate objects.

22 narrow-band H&alpha images were combined into a mosaic covering approx. 41°×23°. In addition, a 4-frame color mosaic was assembled from images taken with a Canon EOS 350D digital SLR camera. In the color mosaic, the R channel was "enhanced" with the Hα data ("lighten only" mode); in addition, contrast-stretched copies of the Hα image were superimposed on the G and B channels, resulting in a "semi-false-color" HαRGB image.