Information...
Here is a SHO false colour image of the North America Nebula (NGC7000) and Pelican Nebula (IC5067) taken by LAS member, James Clark from his back garden in South Harrogate.
The SHO or 'Hubble' palette is used in narrowband imaging, where filters capture particular wavelengths of light, which are then mapped to the Red, Green and Blue channels found in a regular computer screen / TV image. In the SHO palette, the light emitted by ionised sulphur (SII at 671.7 & 673.0 nm) is mapped to the 'Red' channel; light from Hydrogen (Hα at 656.3nm) is mapped to 'Green'; and double-ionised Oxygen (OIII at 500.7 & 495.9nm) is mapped to 'Blue'. Because the Hα and SII emissions are both in the deep-red end of our visible spectrum, regular colour images can't distinguish between the two.
To overcome this problem, the SHO palette was developed by Jeff Hester and Paul Scowen at the Arizona State University in 1995, who were using the NASA Hubble space telescope to study photo-evaporation in the Eagle nebula (M16). The resulting photo, nicknamed 'The Pillars Of Creation' caught the public imagination & soon led to false-colour imaging becoming popular among amateur astrophotographers.
In practice, many narrow band images are tweaked to make them more aesthetically pleasing and less scientific.
Astro-Photography processing software has also advanced in recent years, with the introduction of tools to remove the stars from an image using neural-network machine learning techniques. As well as providing a novel view of deep sky objects, the tools enable the stars to be processed seperately & then recombined with the main image, giving the user much more control over the final result. Two such popular star removal tools are StarNet and StarXterminator.
In James' amazing rendition of the North America and Pelican nebulae, he used a set of filters with just a 3nm bandwidth and was able to capture the data at twilight with only 30 mins for each of the three filters.
