Barnard 33, The Horsehead Nebula, Foraxx Palette

This is a region in the constellation of Orion. The three stars in a diagnal dropping down from the top left corner of the image is the belt of Orion. The Horsehead Nebula, Barnard 33, IC 434, is a dark nebula resembling a horse's head. It is located just below the center of the image. The nebulosity in the image is all part of the Orion Molecular Cloud Complex.

The Horsehead Nebula is silhouetted against an HII Emission Nebula. The HII gas cloud is composed of excited hydrogen gas that glows a deep red (656.28 nm.). Radiation from the multiple star cluster, Sigma Orinus, excites the hydrogen gas causing it to glow. Sigma Orinus is located at the center in the image. (NSF, NOIRLAB)

To the left of the Horsehead nebula is the emission nebula, the Flame Nebula, NGC 2024. (TheSky Professional)

A formula is used to assign pixel values to the RGB channels. The purpose is to more closely emulate the classic Hubble Palette. The specific palette I used is the Foraxx Palette.

(PixInsight Forum)

The color mapping, for this image, is as follows:

Red: (OIII^~OIII) * SII + ~(OIII^~OIII) * Ha

Green: ((OIII*Ha)^~(OIII*Ha))*Ha + ~((OIII*Ha)^~(OIII*Ha))*OIII

Blue: OIII

Bottom line, this mapping communicates the composition of different regions in the nebula. It does not represent the way the nebula appears to our eyes. In this image, the dominant yellow/orange indicates a strong hydrogen (H-alpha) with some sulfur (SII) emission.

Image processed by Andrew F. Macica, original data from Telescope Live.

Imaging Details:

Observatory: IC Astronomy Observatory, Oria, Almería, Spain

Telescope: Takahashi FSQ-106EDX4

Aperture: 106 mm, w/ 0.73x focal reducer, f/3.6

Focal Length: 382 mm

Camera: FLI ProLine PL16803 CCD

Filters: Ha, SII, OIII

Total Exposure: 13 hours 5 minutes

Image Processing:

PixInsight 1.8.9-3 Ripley (x64);

BlurXTerminator, NoiseXTerminator, StarXTerminator (RC Astro);

Python 3.9;

Adobe Photoshop 25.12.1;

Adobe Lightroom Classic 14.2

Instruction on PixInsight from Adam Block Studios.