THE CRESCENT NEBULA
NGC 6888 • Wolf–Rayet bubble • Cygnus • 5000 light-years from Earth
🔭
Askar FRA400
📷
ZWO 2600MC Pro
🌃
Bortle 8
⏱️
25 hours
🗓️
July 2022
Overview
The Crescent Nebula, also known as NGC 6888, is a bright emission nebula located around 5000 light years from Earth in the constellation Cygnus. It formed when fast stellar winds from a hot, massive star collided with slower moving material ejected during an earlier stage of the star’s life, driving powerful shockwaves through the surrounding gas. The Crescent itself is embedded within much larger sweeping clouds of hydrogen, visible here in red, which frame the nebula and add to the sense of scale in wide field astrophotography.
Background
Although the Crescent Nebula itself is a bit small for my wide-angle 400mm Askar FRA400 telescope, it’s surrounded by nebulosity I figured would look good! My ZWO ASI 2600MC Pro camera has a fairly large sensor, and combined with the FRA400 gives a good field of view.
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Science
Although I knew that the Crescent itself is really too small to do justice in my telescope, I did have a punt on making an extreme crop to see it better. Lightroom’s Enhance function allowed me to upscale the resolution quite effectively (and of a higher quality than I got with Topaz Gigapixel AI). The result is better than I expected. The outer shell of Oxygen, shown in blue, is quite evident:
When editing the full image, I noticed a strange tiny circular object. At first I thought it was an artifact left over from the star removal stage during processing, but it didn’t look quite right for that. I did some research and found that it’s actually the Soap Bubble Nebula, a planetary nebula. It was discovered only about 15 years ago, by an amateur astronomer using a 160mm refractor. It’s quite amazing that with modern camera sensors and processing techniques it can be imaged from the centre of a city using a small aperture (72mm) refractor. Click on the full image at the top of this page and see if you can spot the Soap Bubble. Clue if you need it: look a little below the Crescent Nebula.
Kit list
This is the equipment I used to capture the image.
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Telescope: Askar FRA400
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Camera: ZWO ASI 2600MC Pro
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Guidescope: William Optics 32mm Slide-Base Uniguide
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Guidecam: ZWO ASI 120MM Mini
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Control: ASIAIR Plus
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Filter: Optolong L-eXtreme
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Processing
This was relatively straightforward, but I did try using Generalised Hyperbolic Stretch to take the data to non-linear; and NoiseXTerminator for noise reduction. Also, I liked the strong red colours in the image, so didn’t split the channels to create any kind of pseudo-Mono style picture.
It took a bit of teasing to get the faint nebulosity out. Use the slider below to compare a single sub-frame to the final, edited image. These slider comparisons make the whole process seem like magic!
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Example source data
Here’s an example single subframe and freshly integrated stack, just with simple stretches applied.
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Great to see some new content (I need to catch up on your site) – you actually inspired me to get my stuff up on a WordPress site.
I’ve been using StarXTerminator and NoiseXTerminator a bit now .. so much so I’m re-doing some of my older content with newer processes.
I’m impressed with your integration times! I’m still sub 4-5 hours on most targets.. I plan to beef most up to 10-15+ . I’m loving the new 16bit sensors and how sensitive they are.
Like you, I thought the Soap Bubble was a reflection, and spent hours trying to clone it out … need to reprocess again with it back in haha!
I couldn’t get my head around GHS, I’m still lazy.. most of my imaging is targets using the L-Extreme, so I’m using EZ Stretch and then extracting/manipulating and a channel combination as fake SHO. (although I have a SII/OIII Dualband filter on back order..)
Take care, clear skies!
Luke
Thanks for the comment Luke! Give GHS a good go, it can give great results 🙂