About the nebula:


The heart nebula is a huge star factory in the constellation of Cassiopeia. A cluster of young bright stars in the centre have ionised and blown away the surrounding gas creating a heart shaped bubble. Where the hot ionised gas meets the huge surrounding cloud new stars and dark shadows of dense photo star regions are revealed against the backdrop of the bright ionised gas.

The nebula is huge! 7500 light years away and 165 lightyears across. It is over 4 times the size of the full moon in the sky but too dim to see with the naked eye. You would need an 8m telescope to see it! It is located in the Perseus arm of our galaxy so is a close galactic neighbour.

This photo was taken using a set of narrowband filters that only let through light emitted by specific ions in the gas. Sulphur, Hydrogen and Oxygen. These are mapped to red, green and blue to create a false colour image. In reality the hydrogen would produce a deep red colour and makes up most of the nebula so it would appear nearly completely red.

The centre of the nebula in the image appears blue due to the emission from oxygen ions driven by the hight temperatures in the centre of the nebula heated by the central star cluster. The outer regions are cooler and dominated by the sulphur and hydrogen emission lines.

How the image was taken:

This image was taken with a specialised camera and telescope. The telescope is on a motorised mount that rates in the opposite direction to the earth’s spin so that it remains pointed at the same region of the sky even as the earth rotates. This allows photos to be exposed while keeping the image of the nebula projected onto the camera sensor with an accuracy in microns for up to 5 minutes. That’s the width of a human hair! Even after 5 minutes the nebula is so dim compared to the atmosphere of earth at night (especially in my light polluted garden) that the resulting image would be too noisy to see many details. So many images are averaged together to produce the final result. In this case over 8 hours of exposure were used!

I'm still working on the channel combination in my narrowband images. This is the first time I've been able to combine that channels in the linear stage. I tried some slightly different methods to get the colour balance right but it's still a learning process.

This is my longest integration yet and I'm really pleased with some of the detail in the nebula.

Processing steps were
Dynamic Crop
DBE
Copy Ha channel as luminance

Colour processing:
Linear fit and SHO channel combination
SCNR to green channel
Manual colour calibration and background neutralisation
Hue Curves transformation to reduce residual green tint from the stronger Ha channel
TGV and MMT denoise (quite severly)
Saturation adjustment for nebula
Fix magenta stars script
Slight histogram stretch
ACDNR
Masked stretch.

Luminance processing:
TGV and MMT denoise
Deconvolution
Slight histogram stretch
ACDNR
Masked stretch.
Exponential transform
Remove stars using Starnet
HDR
MLT and unsharp mask sharpening
dark structure enhance script
Replace stars in image
LRGB combine

Final tweaks:
Starnet to extract starless layer and star mask
Morphological reduction to image with stars
Pixel math combo for starless, reduced stars and original image.
Saturation and brightness adjustments using range and starmasks.
Final ACDNR pass.