2023: Missouri – The Consigned to Oblivion – Clamshell Nebula SH2-119 in One Shot Color Dual Narrowband.

About this project

I had the opportunity to take advantage of a rare stretch of clear nights and decided to try my luck at capturing a very faint target. According to my research, the magnitude of Sh2-119 varies depending on the wavelength of the light and the area of the nebula that is measured. Sky and Telescope estimates its magnitude at 13.5. Since this was a challenging object to capture, I dedicated three nights and over 30 hours to collecting several hundred long exposure images – precisely 388. Processing these images will be a fun challenge.

About the object

According to web search results, the number of stars in the Cygnus constellation varies depending on how they are counted. The constellation is made up of nine main stars that form its shape in the sky, but it encompasses many more stars within its area. Some sources report 378 discovered stars in Cygnus, while others indicate that there are ten stars known to have planets. Deneb is the brightest star in the constellation and one of the brightest stars in the night sky. It is also the most distant first-magnitude star. There are six named stars in Cygnus: Sadr, Aljanah, Fawaris, Albireo A, Zeta Cygni, and Azelfafage. Cygnus is a rich and fascinating constellation that contains many other interesting objects, such as nebulae, galaxies, and possibly a black hole.

The Cygnus Constellation

Sh2-119 is an emission nebula located in the constellation Cygnus, approximately 2200 light years away from Earth. It’s also known as the Clamshell Nebula, named after its unique shape and structure. The nebula is a combination of gas and dust, illuminated by blue-white stars. This ionization causes the gas to glow, producing the nebula’s characteristic red and blue colors. The nebula is also home to several dark clouds, which are regions of dense gas and dust that block out the light from the background stars. These stars are formed from clouds of gas and dust. As they age and exhaust their nuclear fuel, they release this material back into space, which helps in the formation of new stars and planets.

Sh2-119 is a faint and diffuse object that emits mostly red and blue light. This is due to the ionization of hydrogen and oxygen atoms by nearby stars like 68 Cygni. The complex contains several brighter emission patches and dark nebulae, each with its own LBN and LDN designations. To observe and photograph Sh2-119, you will need a telescope and long exposures as the nebula is much dimmer than its surrounding stars.

The magnitude of Sh2-119 is a complex function of several factors, including its surface brightness. The surface brightness is measured in magnitudes per square arcsecond, which indicates how bright each unit of the area appears in the sky. The surface brightness of Sh2-119 varies across different regions of the nebula, ranging from 20 to 25 magnitudes per square arcsecond, depending on the filter and location. This means that some parts of the nebula are barely visible while others are more easily detected.

Sh2-119 is often overlooked, it is located about 2 degrees west of North America and Pelican Nebulae and about 9 degrees west of the bright star Deneb. The best time to observe Sh2-119 is when it is high in the sky, away from the horizon, and light pollution. The constellation Cygnus is in the northern hemisphere from June to December and in the southern hemisphere from September to November.

The optimal time is around August and September when Cygnus is near the zenith at midnight. To capture its details, you will need a dark sky, a telescope with a wide field of view, and a narrowband filter to enhance the contrast of the nebula.

SH2-119 is a popular target for amateur astronomers. It can be seen with a small telescope, but it is best viewed with a larger telescope and a narrowband filter. Narrowband filters allow astronomers to isolate specific wavelengths of light, such as the hydrogen-alpha line. This allows them to see the nebula’s structure in more detail.

Alternatively, you can use a service like TelescopeLive to remotely access a professional telescope and take images of Sh2-119 without leaving your home.

SH2-119 is a beautiful and fascinating object, and it is a great example of the diversity of objects that can be found in the Milky Way galaxy.

Here is a summary of the key properties of SH2-119:

  • Type: Emission nebula
  • Constellation: Cygnus
  • Distance: 2200 light-years
  • Size: 100 light-years
  • Apparent magnitude: 10.2
  • Spectral type: G5 V

This view is 120 seconds of Sh2-119 – see all of those stars. My job is to reveal all of the nebulae within the star field.

Sh2-119 (Clamshell Nebula) – see all of those stars. A single 2-minute exposure.

Observing Details

Night 1 – Arrived at 615 p.m., temps 51°, seeing was 60% regular, 0% clouds, wind 5 mph, 52% humidity and dew point of 37° F. I departed at 505 a.m.

Night 2 – Arrived at 635 p.m., temps 55°, seeing was 63% regular, 3% clouds, wind 3 mph, 67% humidity and dew point of 41° F. I departed at 611 a.m.

Night 3 – Arrived at 617 p.m., temps 57°, seeing was g00d, 0% clouds, winds 3pmh, 51% humidity and a dew point of 46° F. I departed at 505 a.m.

Location in the Sky

Astrobin Sky Plot – red box shows the location of Clamshell Nebula

Annotated Image

Annotated using scripts in Pixinsight

About the Imaging Location

The Whetstone Conservation Area is becoming my go-to dark sky location. The area is managed by the MDC and it covers over 5,207 acres of unspoiled nature. The place offers incredible views to the North, West, and East, with two noticeable yet tame light domes to the Northeast and Southwest. At nighttime, you can hear crickets, birds, owls, and coyotes.

There are pit toilets and lots of lakes and camping areas located about 2-3 miles down a gravel road, which can be a little intimidating at night. It’s better to arrive during the day to avoid any inconvenience. The place rarely gets crowded, and you can enjoy the serenity of nature. Please note that the area is frequently patrolled by conservation agents to ensure the safety of all visitors.

Equipment used

Night 1 – RedCat51 with ASI2600, and FRA400 with ASI6200 – I noticed some vignetting on images with the latter scope. I will need to revisit the spacing.

Night 2 – RedCat51 with ASI2600. FRA400 with ASI6200. In the latter scope , I removed the filter drawer earlier and saw what caused the vignetting, but I forgot a critical spacer and could not achieve focus. I did not use this scope.

Night 3 – RedCat51 with ASI2600, and FRA400 with ASI6200 – I figured out the spacer issue, and vignetting was resolved, the FRA400 is ready for imaging.

An unstacked single 5-minute exposure image using a Hydrogen-beta and Sulphur II filter, this is a faint object and see the vignetting (dark triangles) in the corners

Acquisition details

Right Ascension: 21hr 16′ 00″ and Declination: 43º 43′ 00″

When I capture images in astrophotography, I usually use 300 seconds of exposure, as it is believed that longer exposures produce less noise in the image. However, during a recent discussion with experienced astrophotographers, they suggested that I try reducing the exposure time to 240 seconds to capture more dim details and not blow out fine details. Since this is deep sky astrophotography, we stack the images, so capturing images with longer total imaging times is more important than longer sub-exposures. For this imaging session, I will prioritize capturing more subs for a longer total imaging time, and if I like the results, I may even try reducing the exposure time to 180 seconds. However, there are some significant factors to consider, such as seeing, transparency, and sky class rating, which will ultimately determine the best exposure time. Only time will tell.

Night 1: Exposure (gain: 100.00) -10°C bin 1×1

Ha/OIII 5nm filter – 70 frames by 300″ (5h 50min)

Hb/SII 5nm filter – 70 frames by 300″ (5h 50min)

Night 2: Exposure (gain: 100.00) -10°C bin 1×1

Ha/OIII 5nm filter – 24 frames by 600″ (4hours)

Hb/SII 5nm filter – 24 frames by 600″ (4 hours)

Night 3: Exposure (gain: 100.00) -10°C bin 1×1

Ha/OIII 5nm filter – 100 frames by 240″ (6h 40mins)

Hb/SII 5nm filter – 100 frames by 240″ (6h 40min)

Total exposure time: 33h

Lights: 388 | Dark Cal Frames: 388, Flat Cal Frames 150, and Flat Cal Darks 150.

Image captured from a Bortle Class 3 Dark-Sky.

Processing time

I loaded 388 Light frames using the Weighted Batch Preprocessing script in PixInsight. After that, I calibrated the lights with Dark, Dark Flats, and Flats, then stacked all of the registered 388 measured light frames, only 27 were rejected. The entire process took 5 hours and 48 minutes.

Stacking is vital for astrophotography because it allows astrophotographers to capture detailed images of deep-sky objects without having to use extremely long exposure times.

Deep-sky objects, such as galaxies, nebulae, and star clusters, are very faint and require long exposure times to capture. However, long exposure times can also introduce noise into the image. Stacking helps to reduce this noise by averaging multiple images together.

The more images you stack, the greater the noise reduction and the more detailed the final image will be. However, it is important to note that there is a point of diminishing returns. After a certain number of images are stacked, the noise reduction is minimal, and adding more images will not significantly improve the image quality.

Stacking is also useful for astrophotographers who do not have access to dark skies. Light pollution can add noise to astro-photographs, but stacking can help to reduce this noise.

Here are some of the benefits of stacking for astrophotography:

  • Reduces noise: Stacking averages multiple images together, which reduces random noise. This can be especially helpful for imaging deep-sky objects, which are often very faint and noisy.
  • Increases signal: Stacking also increases the signal strength of the objects being imaged. This makes them appear brighter and more prominent in the final image.
  • Improves dynamic range: Stacking can also improve the dynamic range of the final image. This means that more detail can be visible in both the bright and dark areas of the image.
  • Reduces risk of over-exposure: Stacking allows astrophotographers to use shorter exposure times, which reduces the risk of over-exposing the image.

Overall, stacking is a powerful technique that can help astrophotographers capture high-quality images of deep-sky objects.

An unstacked single 5-minute exposure image using a Hydrogen-alpha and Oxygen III filter

Software Used

  • Pleiades Astrophoto PixInsight
  • Russell Croman Astrophotography StarXTerminator
  • Russell Croman Astrophotography BlurXTerminator
  • Russell Croman Astrophotography NoiseXTerminator
  • Adobe Lightroom Classic
  • Adobe Photoshop

Final Images and Thoughts

When processing an image in Pixinsight, to reveal the detail of the nebula, it is advised to remove the stars.

A stacked image using Hydrogen-alpha and Oxygen III filter – SH2-119 “Starless”


A stacked image using Hydrogen-beta and Sulphur II filter – SH2-119 “Starless”

If you are an astrophotographer, you may have seen or heard about the Hubble Telescope. One of its most iconic images is the “Pillars of Creation. The Hubble Palette, named for an image processing technique done by the Hubble Space Telescope team, creates what is called “false color” imaging by using narrow-band filters and assigning the data captured with each narrow-band-filtered channel to one of the red, green, or blue colors in an RGB image. SHO refers to the first letters of the narrow-band filters—SII, Ha, OIII. The technique and its use of false colors help to see very well the Pillars’ overall structures in the emission lines. Each color can represent a specific element. In other words, a false-color image of a nebula tells us exactly what it’s made of. There are many emission lines, but the three most commonly photographed by astronomers are hydrogen-alpha, oxygen-III, and sulphur-II. These emission lines are captured by using narrowband filters which only let through the light at very specific wavelengths, typically with a bandwidth of 12µm or less.

Element Emission line Wavelength Color

  • Hydrogen Hα 656.3 nm Red
  • Oxygen O-III 500.7 nm Green
  • Sulfur S-II 672.4 nm Red

Mapping Hα, O-III, and S-II to red, green, and blue is problematic when two of them are red, one is green and none is blue. Astronomers deal with this by using false color — one or more of these elements is going to have to take a hit for the team and take on an unnatural hue. The Hubble palette assigns red to SII, green to Hα, and blue to O-III: red is accurate, green and blue are false. Have I lost you yet? Well, hold on it gets better.

Green isn’t absent from space, the problem with green is that it’s right in the middle of the visible spectrum, so any star that’s producing a large amount of green light is also producing a large amount of light in all colors. Such a star, like the Sun, looks white. Very hot stars will look blue, rather than violet. Stars only range from red to light blue, dependent solely on their temperature. But green glows do exist in space, arising from heated gas. When electrons transition between different energy levels, they emit light at specific, well-defined frequencies.

So while the Hubble color palette is beloved and well used, I decided on a different path and I use the Foraxx color palette. What is Foraxx Palette Script? A new script has now been released by Paulyman Astro, which automates the process of creating narrow-band images in the Foraxx palette. The Foraxx palette makes use of so-called dynamic narrowband combinations, as published by The Coldest Nights. Compared to Hubble palette images, Foraxx images have their look with often more bronze colors in them and less dominant blues.

The script works for narrowband images from monochrome cameras, as well as OSC cameras with dual-band filters. It requires the stars to be separated from the nebulosity, so star removal is a prerequisite. This is typically a one-click operation using tools such as Starnet2 or Russ Croman’s StarXTerminator.

Here is the result of using the Foraxx Color Palette

Here is the resulting image from 33 hours of image capturing – This image is the result of combining Hydrogen-alpha/Oxygen III and Hydrogen Beta/Sulphur II filters. I processed using a Foraxx Palette in Pixinsight and Adobe Lightroom Classic

Until the next adventure and thank you for stopping by!

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  1. What a cool project, Miguel! Obviously a lot of time and effort went into this. Congratulations on this. The writing on this piece is also extraordinary. Learned a lot!

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