Taking advantage of the fact that narrow band imaging is relatively unaffected by a full moon in the sky (and the 50% discount in telescope cost) I added another two 15 minute Ha exposures to my collection of the Horsehead. Then the pain-staking process of combining the individual frames to make a single pleasing colour image could begin.
All the frames were calibrated and aligned in Maxim DL and the red, green and blue frames combined to make a single RGB image. A Digital Development Process stretch was then applied to all images and they were saved as 8-bit tiff images for further processing in Gimp (my favourite open source image processing software).
The bright star is Alnitak, the left hand star in Orion’s belt. The radiation from this star lights up a hydrogen gas cloud making it glow red and the Horsehead itself is a dark cloud of gas and dust silhouetted against the bright background. The Flame nebula (NGC 2024) is formed in a similar manner. Just below the Horsehead is NGC 2023, a bright reflection nebula. 1500 light years away, the Horsehead is some 3.5 light years in height (or 2×1013 miles high).
