This image is the result of layering the OIII data on top of the Ha data twice then running Noel Carboni's Synthetic Green action, which replaces the middle layer with a combination of the Ha and OIII layers to make a synthetic green yielding a more traditional looking RGB image.
The 1' subexposures badly overexposed the core of the nebula, as expected. So I made a series of 15" exposures for each channel to use for the core. I aligned and combined the long exposures in ASIP and then RGB merged them in Photoshop. I RGB merged the short exposures in Photoshop and then added them to the long exposure version as a layer with a "hide all" layer mask. Then select the layer mask and paint over it with a white brush with very low opacity in the brush to reveal the core slowly.
Description:
M42
Possibly discovered 1610 by Nicholas-Claude Fabri de Peiresc.
Independently found by Johann Baptist Cysatus in 1611.
Trapezium cluster found as multiple star by Galileo Galilei in 1617.
The Orion Nebula M42 is the brightest diffuse nebula in the sky, and one of the brightest deepsky objects at all. Shining with the brightness of a star of 4th magnitude, it visible to the naked eye under moderately good conditions, and rewarding in telescopes of every size, from the smallest glasses to the greatest Earth-bound observatories as well as outer-space observatories like the Hubble Space Telescope. It is also a big object in the sky, extending to over 1 degree in diameter, thus covering more than four times the area of the Full Moon.
