THE BUTTERFLY NEBULA
IC 1318 • Emission nebula • Cygnus • 4000 light-years from Earth
🔭
Askar 130PHQ
📷
ZWO 2600MC Pro
🌃
Bortle 8
⏱️
35.5 hours
🗓️
July & August 2023
Overview
The Butterfly Nebula, also known as IC 1318, lies around 4000 light years from Earth and forms part of the wider Sadr region in the constellation Cygnus. Centred near the bright star Gamma Cygni, this area is rich in glowing gas and complex dark structures shaped by ongoing star formation. Although this image spans roughly 80 light years in physical size, the region covers only a tiny patch of sky, about twice the width of a thumbnail held at arm’s length, highlighting just how vast these structures are despite their subtle appearance from Earth.
Background
Cygnus is high overhead as seen from the UK this time of year, and it’s full of intricate nebulae. My Askar 130PHQ telescope has a focal length of 1000mm, which means it’s well suited for tight framing, detail-oriented shots. For this project I chose the Butterfly Nebula (not to be confused by a planetary nebula with the same name) because it looked interesting and would entirely fill the frame edge-to-edge.
As is now my standard practice for these types of nebulae, I used an Optolong L-Ultimate filter for Hα and OIII data; an Askar D2 filter for SII and more OIII; and then no filter just for the stars, to give them fairly accurate colours. So it’s an SHO image from an OSC camera. In terms of integration times, the L-Ultimate is 15 hours; D2 is 20 hours; and the no filter RGB stars is just 30 minutes (stars are really bright so you don’t need much time on them).
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Science
I was surprised to discover that I’d actually managed to image two extremely faint planetary nebulae that are within the Butterfly Nebula. They have the official designations PK078+0.01, and PK079+0.01.
Don’t let the name fool you: planetary nebulae aren’t actually anything to do with planets. Rather, they’re shells of gas being released from low-mass stars reaching the ends of their lives. Early astronomers thought they looked a bit like the disks of planets when seen through their telescopes, and the name stuck.
Kit list
This is the equipment I used to capture the image.
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Telescope: Askar 130PHQ
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Camera: ZWO ASI 2600MC Pro
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Mount: Sky-Watcher EQ6-R Pro
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Guidescope: William Optics 50mm with ROTO Lock
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Guidecam: ZWO ASI 120MM Mini
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Control: ASIAIR Plus
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Filter: Optolong L-Ultimate
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Processing
I’m receiving a lot of requests for a processing guide for this approach, and I plan to make one soon. Meanwhile, I made what I think is an interesting comparison of the data sources. I took just the Optolong L-Ultimate data and made a rough edit, producing a starless image. Then I did the same thing with the Askar D2. You can compare them using the slider:
The L-Ultimate data is better quality despite the lower integration time, simply because there’s so much Hα in the nebula. But the D2 is clearly bringing a different wavelength into the mix. My final image is the result of mixing L-Ultimate and D2 data, with RGB stars sprinkled in top.
There are methods of creating pseudo-SHO images from just the stronger Hα/OIII data. Perhaps best-known nowadays is the Bill Blanshan Pixinsight script that does this with a single click. For interest, I ran this script on my L-Ultimate data and gave it a very quick edit:
I much prefer the version with Askar D2 data added, although admittedly it’s a far longer total exposure time and was more fiddly to process.
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Example source data
Here are example single subframes and freshly integrated stacks, just with simple stretches applied.
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