Pickering’s Triangle
NGC 6979 • Supernova remnant filament • Cygnus • 2400 light-years from Earth
🔭
Askar 130PHQ
📷
ZWO 2600MC Pro
🌃
Bortle 8
⏱️
17 hours
🗓️
August 2025
Overview
Pickering’s Triangle is the expanding remains of a massive star that exploded as a supernova sometime between 10,000 and 20,000 years ago. It stretches across 40 light-years of space, with thin, thread-like filaments glowing where shockwaves collide with interstellar gas.
From light-polluted urban skies this structure is extremely subtle, but imaging allows its delicate filaments to be separated from background sky glow and recorded — but only if you’ve got sufficient integration time!
Background
I enjoyed processing my previous two targets (the Lion Nebula and Pelican Nebula) and was in the mood for another frame-filling colourful image. The Cygnus Loop was well-placed in the sky, but the entire object is too large for my Askar 130PHQ telescope. I decided to focus on the lesser-imaged part of this large complex: Pickering’s Triangle.
There’s not much SII in the region, so I just used my Optolong L-Ultimate filter (Hα/OIII), along with RGB real-colour stars. During processing I edited the Hα as orange, and the OIII as blue. The entire project only took a week, thanks to an unusual run of clear skies!
The naming of Pickering’s Triangle is a point of historical interest. The larger Cygnus Loop structure was spotted in 1784 by William Herschel, but its finer structures (including the Triangle) were only discovered in the 1900s when a photographic survey of the area was undertaken by Harvard Observatory. The Triangle was discovered in these photos by Williamina Fleming, but naming honours went to the Observatory’s director: Edward Charles Pickering.
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Science
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- Pickering’s TrianglePickering Triangle
- Supernova remnant regionAlso catalogued as Pickering’s Triangle · Pickering Triangle
- An approximate marker within this filamentary region of the Cygnus Loop. The label is a regional guide, not a catalogue boundary.
About the labels and credits
Positions and outlines are calculated from a plate solution of this photograph. Outlines are catalogue guides and may not follow every visible filament. Additional catalogue objects may be faint or indistinct in this exposure.
The Pickering’s Triangle label is an approximate regional marker based on the NOIRLab reference image; it does not define a nebular boundary.
Plate solving and annotation data: SkySolver, by Dominik Sito. Stars: Gaia DR3 and Hipparcos (ESA). Deep-sky data: OpenNGC © Mattia Verga (CC BY-SA 4.0), SIMBAD and VizieR (CDS). Names: Wikipedia (CC BY-SA 4.0) and IAU WGSN. Catalogue overlay adaptations, including styling and selected display names, are shared under CC BY-SA 4.0. Photograph © Lee Pullen.
The story of Pickering’s Triangle begins 10,000 to 20,000 years ago, when a massive star, 2400 light-years from Earth, exploded as a supernova. The blast tore the star apart, sending shockwaves racing outward at 600,000 kilometres per hour, ploughing into the surrounding interstellar medium.
Pickering’s Triangle is a region where these shockwaves encounter clumps of gas at slightly different densities and speeds. This impact creates the knots and filaments visible in my image, stretching across about 40 light-years. The shockwave heats and ionises the gas. The visible filaments trace gas cooling behind the shock front, while much hotter gas elsewhere in the remnant emits X-rays. Different elements produce different colours: during image processing I mapped hydrogen to orange and oxygen to light blue.
Below are a selection of close-crops highlighting shock fronts, where the supernova’s expanding shell impacts gas and dust, creating rippling effects. I think that each one looks like an abstract painting. Use the slider function for inverted views, which can help make the finer structures easier to see.
Imaging details
- Total exposure
- 17 hours
- Dates captured
- 16 – 22 August 2025
- Location and sky
- Bristol, UK (Bortle 8)
Equipment and software
- Telescope
- Askar 130PHQ Flatfield Astrograph
- Camera
- ZWO ASI 2600MC Pro
- Mount
- Sky-Watcher EQ6-R Pro
- Guiding
- WO 50mm + ZWO ASI 120MM Mini
- Control
- ASIAIR Plus
- Software
- PixInsight, Lightroom
- Image by
- Lee Pullen
Exposure by filter
L-Quad Enhance
- Channels
- RGB (stars)
- Subframes
- 15 × 2 minutes
- Integration
- 30 minutes
View subframe and stack
Single subframe and integrated stack, both with a simple stretch applied.
Optolong L-Ultimate
- Channels
- Hα / OIII
- Subframes
- 198 × 5 minutes
- Integration
- 16.5 hours
View subframe and stack
Single subframe and integrated stack, both with a simple stretch applied.
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-Quad Enhance
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Filter: Optolong L-Ultimate
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Processing walkthrough
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