The Cygnus Loop...

The Cygnus Loop (Sharpless 2-103)...

Objects NGC 6992-5, IC1340 (the Eastern Veil), NGC 6960 (the Western Veil or "Witches Broom"), "Pickering's Triangle" (wedge of nebulosity at "one-o-clock" position above): also NGC 6974 and NGC 6979 (knots of nebulosity to the left of Pickering's Triangle)

Type: Supernova remnant
Constellation: Cygnus
Distance: 2,400 light years

Equipment: Atik 460/EFW 2, Samyang 135mm lens@ F2, Vixen GPDX mount, guiding with Lodestar X2/PHD
Date: August 8th. 2022

Subframes: 18 x 300s for Ha, 12 x 300s for OIII, flats, no darks (hot pixel removal in Astroart). 

High overhead on a summer’s evening can be found the constellation of Cygnus (The Swan), whose brightest star (Deneb) is the top left star of the isosceles triangle of bright stars that dominates the UK summer night-time skies called the Summer Triangle.

Tucked under the Swan’s eastern wing is an enigmatic object, a supernova remnant called the Cygnus Loop. It consists of a bubble of dust filaments and fluorescent gas over 120 light years in diameter, or about 3 degrees across (6 moon diameters) as viewed from Earth, the remains of a supernova that occurred some 15,000 years ago.

The shock wave from that event is ploughing through and compressing the patchy interstellar medium of gas and dust that surrounded the exploding star, causing the rarefied gasses to fluoresce, hence the nebula we see today.

The brighter sections of the Cygnus Loop, NGC 6992-5 (the Veil Nebula) and NGC 6960 (The “Witches Broom”) are just visible through a large (8-inch aperture or more) telescope on clear, moon-free nights. Details of the central area of the bubble can only be detected on long exposure photography.

The five-minute subframes I used here weren’t really long enough to show up all of the available detail, and the stacks required a hefty tangential stretch to show the wispy central areas of nebulosity.

I used Starnet+ to remove the fog of stars in the stacked hydrogen-alpha and OIII images, which allowed some selective stretching and sharpening of the nebulosity. I then used the PSP “erode” function (“magic wand” to select background > invert > feather (3 pixels) > effects > edge > erode) to reduce the star sizes on the “normal” images, and combined the “starry” and “non-starry” images in “blend lighten” mode to give sharp nebulosity and small stars.

To make the colour image, I used the Ha channel as red, the OIII channel as blue and made an artificial green channel of 60/40 OIII/Ha. Combining the three as an RGB image gave the result at the top of this post.

NGC 6960: The Western Veil Nebula...

NGC 6960 in HOO

Object: NGC 6960 
Type: Supernova remnant
Constellation: Cygnus
Distance: 1,470 light years
Date: September 23rd. 2020
Equipment: ATIK 460EX with EFW2, Skywatcher f5.5 Esprit 100 ED refractor, Avalon Linear mount, guiding with Lodestar X2/PHD
Subframes: 10 x 300s Ha, 10 x 300s OIII, no flats, no darks (hot pixel removal in Astroart).

Stellarium map showing location of field of view

Tucked under the eastern wing of Cygnus, NGC 6960 (also nicknamed the “Witches’ Broom”) is a remnant of a supernova that is believed to have occurred approximately   8,000 years ago.  It is part of a larger nebula covering nearly 3 degrees of sky, and which includes the Eastern Veil nebula NGC 6992-5.  The link to my earlier image of the other half of this nebula gives more information about the object.

The image above is an HOO composite. Both seeing and transparency were not good during the evening of September 21st. and the resultant sub-frames were rather noisy, a sure sign of high altitude haze. I was also too lazy to take more or longer ones, although I may revisit this object in the near future. After grappling with a series of objects with very weak OIII signal, at least that of NGC 6960 is reasonably strong and facilitates image processing.