Revisiting An Old Friend

In all of the night sky, both North & South Hemispheres, there’s no other target quite so infamous as the Great Orion Nebula. Everyone can see it with their naked eye, even if they don’t realise that they’re looking at the closest star-forming region to Earth, at approximately 1,350 light-years away. Having a magnitude of +4, it is easily seen from city suburbs and is often mistaken for another star.

Once your eyes are dark adapted and with a pair of decent binoculars, gaze towards the south and located the Constellation Orion. First, find the well known Orion’s Belt, and then slowly move downwards towards the two lower stars of Rigel and Saiph. Somewhere in the middle, you should see a line of three diffuse stars; 42 OrionisTheta Orionis, and Iota Orionis, forming the asterism of ‘Orion’s Sword’.

Theta-1 Orionis is actually a small, open cluster of stars commonly known as the ‘Trapezium Cluster’, located in the heart of the Orion Nebula itself. This is often seen using an eyepiece and averted vision, however it often eludes astrophotographers. Due to the massive dynamic range of the surrounding nebulosity, the trapezium is often obscured in many images caused by over-exposing the core in order to get as much data in the outer fringes of the nebula as possible. It is why the trapezium is often used to judge an image of Messier 42.

The way around this is to take multiple lengths of exposures; shorter exposures for the core, and longer exposures to gather the outer dust. The whole Orion Molecular Cloud Complex, along with other cloud complexes within the local area, can be read about in the American Astronomy Society’s Journal “The Large System Of Molecular Clouds In Orion And Monoceros”.


The Orion Nebula has been eluding me so far in 2022; I’ve taken it as a wide field shot with my Samyang 135mm in my previous post, but not up close and personal with my Sky-Watcher 130PDS. Fortunately though, we have had a string of clear nights in early and late February, which also coincidentally means that Orion now has passed the meridian by the time I get back from home from work. By positioning to the far side of the back garden, I am now able to capture Orion earlier by shooting around the apex of the roof, just after astronomical darkness at 19:30.

The first night was at the beginning of the month, in which I went for the longer exposures, aiming to capture as much of the outer nebulosity as possible. As Messier 42 is classed as a hydrogen emission nebula, I also used my IDAS NBZ filter to further isolate the nebula from the light pollution. This new filter made a huge improvement over my previous version from last year, which was taken with the general light pollution filter, the IDAS NGS1.

Deep Sky Stacker Information

Unfortunately, I was only able to capture 17 exposures on the 4th February, which is one exposure shy of 90 minutes. However, the initial stack within Deep Sky Stacker looked promising so wasn’t worried too much. The project then sat stacked, but unprocessed, on my hard drive for the rest of the month. However, the past few days have been crystal clear all night, allowing me to finish this years version of Messier 42.

You can see how clear the skies were in the image below!

Sky-Watcher Explorer 130PDS + AZ-EQ6-GT Equatorial Mount

For the shorter exposures, I really wanted to highlight the trapezium in the core, so I captured over 200 20-second exposures at a lower ISO setting, giving a total of 1 hour 10 minutes.

Deep Sky Stacker Information

The unstretched exposures within N.I.N.A. (below) clearly show the 4 brightest stars in the Trapezium, right at the core of the nebula. In this image, you can also see my guiding graph, showing a total RMS error of 0.52″; a truly incredible guiding figure for an unhypertuned mount! As the exposures were so short, I decided to dither every 5 exposures, limiting any unnecessary movement of the mount in the process.

Single Unstretched Exposure in N.I.N.A.

I first processed the longer exposure stack within Photoshop CC, making curve adjustments to highlight the outer nebulosity, while also keeping the detail in the large amounts of dark dust that surround the Orion and Running Man Nebulae, some of which can already be seen in the above image on the left in Deep Sky Stacker. Once I was happy, I then edited the shorter stack in a similar vein; very minimal processing while trying to highlight the inner details and not over-expose the brighter stars. Very difficult to get right!

The next step is to then manually align the two images using separate layers in a new photoshop file; this was a relatively painless in all honesty. By using the brighter stars in the top and bottom of the image as guides, it was simply small rotations and movement changes until everything lined up perfectly. The bright overexposed core in the top layer was then removed by using the eraser tool, revealing the detailed core from the layer below. The most challenging part was seamlessly blending the two layers, thus giving the illusion of a single image. This was done by using more curves, levels and other adjustment layers to perfectly colour match the joins. A very painstaking process, with many do-overs to finally get it right!

The final result though is probably the best image that I have produced in the two years that I have been doing Astrophotography. The sheer amount of detail in the surrounding regions, especially between M42 and M43, truly blows me away every time that I look at the image. To think that light leaving those stars 1,350 years ago has travelled for all that time, to be captured by my telescope in my light-polluted back garden. The human brain cannot truly comprehend it!

The Great Orion Nebula – 2 Hours 35 Minutes 40 Seconds

Well, I hope that you’ve had some clear weather recently, wherever you are! I certainly have this month, and I promise it won’t be long until my next post, so stay tuned!

Till then, I wish you all clear skies!

2 Comments Add yours

  1. Ggreybeard says:

    I noticed your post in the the Facebook EQ Users Group.
    Great website and lovely image of M42. That IDAS filter does a good job!
    I’ve barely seen Orion this season, we’ve got constant cloud cover and floods here in Oz.
    🙃

    Like

    1. Thank you! 😄 Means a lot that you took the time to read it!

      I absolutely love my AZ-EQ6-GT mount, and my images would be nowhere near as good as they are without it. And yes, the IDAS is a superb filter in my opinion, as it has no star halo issues like the L-eXtreme is notorious for. My next post by the way will really show how good that filter really is, so stay tuned! 😁

      Liked by 1 person

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