IC443

IC443 is a supernova remnant in the constellation Gemini, just northeast of the bright star Propus. This nebula is thought to have been produced by a supernova explosion about 30,000 years ago. It is 5,000 light years distant. In this image, north is up, and Propus is out of view toward the bottom-right.

This image was exposed through filters having extremely narrow bandwidths to capture only the light emitted by certain gasses when excited by stellar radiation.

The data from the three filters was assigned to this "natural-color" palette in Photoshop. First, the monochrome hydrogen-alpha image was converted to color. Next, the oxygen-III and sulfur-II images were layered one on top of the other, with the blending mode set to "screen" to get data from both images. The two layers were flattened into one, which was copied and pasted into the blue channel of the RGB-mode H-a image, leaving the H-a data in the red and green channels. Finally, the green channel was replaced with data synthesized from the red and blue channels using Noel Carboni's Astronomy Tools for Photoshop.