The Horsehead Nebula, Barnard 33, IC 434

The Horsehead Nebula, Barnard 33, IC 434, is a dark nebula resembling a horse's head. The dark nebula is part of the Orion Molecular Cloud Complex. It is located in the eastern most region of the belt of the constellation Orion.

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 above center in the image. (NSF, NOIRLAB)

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

This image images is a narrowband image. Ionized gases in this nebula produce three prominent emissions: Hydrogen Alpha (656.3 nm), Sulfur II (672 nm) and Oxygen III (500.7 nm).

A formula is used to assign pixel values to 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: Heaven's Mirror Observatory, Yass, Australia

Telescope: Takahashi FSQ-106ED

Aperture: 106 mm (4.17 inches), f/3.6

Focal Length: 382 mm (with 0.73x focal reducer)

Camera: QHY 600M Pro CMOS

Filters: Ha, SII, OIII

Total Exposure: 8 hours 45 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.