NGC 896 & IC 1795: The Fish-Head Nebula...

NGC 896 & IC 1795 - The Fish Head Nebula

Object: NGC 896, IC 1795
Type: Emission Nebula 
Constellation: Cassiopeia
Distance: 6000 light years

Date: 15th and 17th January 2020
Equipment: ATIK 460EX with EFW2, Skywatcher f5.5 Esprit 100 ED refractor, Avalon Linear mount, guiding with Lodestar X2/PHD

Subframes: 25 x 300s H-alpha, 20 x 300s OIII (2x2 binned), 6 x 300s each for RGB (2x2 binned), no flats/darks (hot pixel removal in Astroart).

Stellarium map showing location of IC 1745

High in the winter north-western sky (close to the Double Cluster in Perseus), NGC 896 is a relatively bright knot of nebulosity which forms part of a wider area of nebulosity designated as IC 1795, itself part of the larger IC 1805/IC 1848 complex ( the “Heart and Soul Nebula”). It is approximately 20 arc-seconds across, appearing to occupy an area in the sky around two-thirds of the full moon. 

Discovered by William Herschel in 1787, NGC 896 lies at the edge of a large molecular cloud located in the distant Perseus spiral arm of the Milky Way Galaxy. The area around NGC 896 is also a strong source of radio emissions.

The hydrogen alpha frames were taken on the 15th. I took some 300s unbinned OIII subs the same night, but a combination of high haze and a rising gibbous moon washed them out. The OIII signal of IC 1795 is also comparatively weak compared to the Ha, so I went for 2x2 binned subs at the next available opportunity.  In hindsight, I should have gone for longer exposures in narrowband as both Ha and OIII stacks were pretty noisy, as were the RGB subs.

I prepared an RGB colour frame from red, green and blue stacks and a HOO frame from the narrow band stacks, both in PaintShop Pro.  I then combined the two to give a balanced colour mix, and then overlaid the Ha stack as a luminance layer. Selective sharpening and curves in PaintShop gave the final image.  I had to hit the narrowband stacks with noise reduction a bit harder than I would have liked as they were fairly noisy, so the stars are a bit fuzzy. This is a bit frustrating as sky conditions were (for once) excellent on the 17th, and I could easily have taken much longer exposures.

I had previously imaged this area in December 2007 as a two-frame wide-field mosaic using a 135mm camera lens. The image below shows the relation of IC 1795 to IC 1805 and IC 1848.

Emission nebulae IC 1848, IC 1805 and IC 1795 in Cassiopeia.