The Great Pumpkin Nebula

An orange sphere that seems inflated from within, crossed by dark veins: in this image, Sh2-232 lives up to its nickname, the Great Pumpkin. This vast nebula lies in the constellation Auriga, about 6,200 light-years away. It is number 232 in the catalogue published in 1959 by the American astronomer Stewart Sharpless, which lists the regions of ionized hydrogen visible from the northern hemisphere. It spans about 40 arcminutes of sky, more than the apparent diameter of the full Moon, or roughly 70 light-years from edge to edge.

Sh2-232 is an HII region: a cloud of gas ionized by the ultraviolet light of hot, massive B-type stars. As it recombines, hydrogen emits the red light of the H-alpha line, and sulphur that of the SII line. The nebula belongs to the giant molecular cloud G174+2.5, a stellar nursery that also hosts the nebulae Sh2-231, Sh2-233 and Sh2-235.

The image was made in the HSO palette: hydrogen is shown in red, sulphur in green and ionized oxygen in blue. The outer shell, where hydrogen and sulphur dominate, takes on this golden hue, while the core turns magenta where oxygen adds to hydrogen. The sharp dark filaments in the upper part of the sphere are cold, dense dust lying in front of the glowing gas and blocking its light. Oxygen is the faintest signal in this nebula: it took 7 hours of exposure for it alone, out of a total of 29 hours.