Current thinking suggests that IC 443 is the remnant of a type II supernova that occurred between 3,000 and 30,000 years ago, leaving a neutron star at the centre. IC 443 is one of the best examples of a supernova remnant interacting with surrounding molecular clouds.

The nebula contains a number of sub-shells of different radii, emissions and centres. There is a larger north eastern shell caused by a 100 km/s shock wave and a smaller south eastern shell caused by a 30 km/s shock wave. A third larger shell is believed to be from an earlier supernova explosion about 100,000 years ago. It is useful to note that in this image north is to the top and east is to the left side of the photograph. This appears to be laterally inverted when compared to a terrestrial map, however, here we are dealing with the heavens and when looking up to the southern sky, the eastern horizon is down to the left and western to the right.

The nebula is positioned between two bright variable red giant stars that represent the feet of Castor, who stands next to his Geminian twin Pollux. To the left is Mu Geminorum (Tejat Posterior, back foot) at a distance of 230 ly, which is both cooler and brighter than the Sun. To the right is Eta Geminorum (Propus, front foot), a triple star at a distance of 350 ly. The primary is a spectroscopic binary with a period of about 8 years. The secondary is a dwarf star with an orbital period of about 700 years. These stars are much nearer and appear about 4000 times brighter than the nebula.

This extreme brightness created significant problems during processing. It was necessary to continually mask the two bright stars so that the relatively faint surrounding nebulosity could be developed without overexposing the area of the stars.