Overview
The bright star in the top-left is called Gamma Cassiopeiae, and is around 550 light-years from Earth. It’s almost 20 times more massive and 65,000 times brighter than the Sun, and rotates so fast — 1.6 million kilometres per hour — that it blasts out intense ultraviolet radiation, eroding the nearby Ghost Nebula and causing hydrogen gas to glow red. Other parts of the nebula reflect Gamma Cassiopeiae’s strong blue light.
Background
Like most of my targets this object is really faint, so I needed to collect a lot of data to get a decent image from my light-polluted city centre location. The final image contains 32 hours of light, collected over nearly seven weeks. For tips on achieving long integration times, check out my article here. Despite all that it’s still quite noisy, but I’m happy considering it’s a bit of a feat to image it to any degree under my skies!
Being a reflection and emission nebula meant that I decided to collect data using my Optolong L-Quad Enhance (for RGB) and Optolong L-Ultimate (for Ha and OIII). I used this approach recently for the Flaming Star Nebula and it worked well. For more info, check out my guide to choosing filters for your OSC camera. Use the slider below to compare quick edits of the RGB and Ha/OIII data. You can see how various elements from both make it into the final image. I think it’s interesting from a scientific viewpoint too, as when looking at the two images side-by-side you can compare the emission (red) and reflection (blue) elements really well:
Imaging details
| Date | 3 March to 18 April 2024 (6.5 weeks) |
| Location | Bristol, UK (Bortle 8) |
| Telescope | Askar 130PHQ Flatfield Astrograph |
| Camera | ZWO ASI 2600MC-PRO |
| Mount | Sky-Watcher EQ6-R PRO |
| Guide | William Optics 50mm Guidescope with 1.25″ RotoLock; ZWO ASI 120MM Mini |
| Control | ASIAIR Plus |
| Software | PixInsight, Lightroom |
| Filters | – Optolong L-Quad Enhance (RGB) 192 x 300 seconds (16 hours) – Optolong L-Ultimate (Ha/OIII) 192 x 300 seconds (16 hours) |
| Total exposure time | 32 hours |
| Image credit | Lee Pullen |
Processing
The halo around Gamma Cassiopeiae is big and nasty, and was a pain to remove during processing. I outline how I went about this in the processing video below. (Spoiler alert: I used Photoshop’s new Generative Fill function).
Source data
Seestar S50
To be added later…
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