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Contains:  NGC 246
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NGC 246 Skull Nebula HaOIII + RGB stars (12.2 hours), 


            Barry Brook
NGC 246 Skull Nebula HaOIII + RGB stars (12.2 hours)

NGC 246 Skull Nebula HaOIII + RGB stars (12.2 hours)

Technical card

Resolution: 1416x1096

Dates:Sept. 20, 2014

Astronomik Ha 12nm 1.25'': 18x1200" 3C bin 1x1
Astronomik OIII 12nm 1.25": 18x960" bin 1x1
ZWO optical ZWO RGBL Filters: 84x60" bin 1x1

Integration: 12.2 hours

Darks: ~70

Flats: ~100

Bias: ~500

Avg. Moon age: 26.13 days

Avg. Moon phase: 12.52%

Bortle Dark-Sky Scale: 6.00

Temperature: 7.00 job: 380644

RA center: 11.772 degrees

DEC center: -11.870 degrees

Pixel scale: 1.244 arcsec/pixel

Orientation: 91.327 degrees

Field radius: 0.309 degrees


NGC 246, "The Skull", is a eerie-looking planetary nebula in the constellation Cetus, about 1600 light years distant. It has an angular diameter of 4.5'. The central white dwarf (part of a binary) was mag 9 in 1930 but has since dimmed to mag 12. The complex braided structure is a result of shock waves as the dying star expelled its outer layers.

The image was captured in narrowband from my Adelaide surburban backyard, using an Skywatcher 120 mm achromat refractor (at f/4), mounted on an AZ-EQ6. This telescope is excellent for narrowband work as it has a decent aperture, fast focal ratio, and under these conditions, doesn't suffer from CA. The CCD camera was an Orion StarShoot G3 mono (dithered and drizzled), guided with PHD2 using a thin OAG and an ASI120MM-S guide camera.

The image is composed of the following:
Ha = 18 x 20 min
OIII = 18 x 16 min
R, G & B = 28 x 60 sec for each channel

Total integration time = 12.2 hours.

Synthetic luminance channel was created by blending an exposure-based weighting of the Ha, OIII, R, G and B. All subs were unbinned. Nebula colour was mapped as Ha:Ha:OIII.

Captured over the period 19 to 22 Sept 2014. Pre-processed with flats (light box), bad pixel map (based on 70 darks) and bias in Nebulosity. Aligned and Drizzled in DSS. Post-processed in StarTools.



Barry Brook
License: Attribution Creative Commons

Sky plot

Sky plot


NGC 246 Skull Nebula HaOIII + RGB stars (12.2 hours), 


            Barry Brook