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IC 4592 - The Blue Horsehead Nebula - Astrophotography

Updated: Aug 14

IC 4592 is a beautiful reflection nebula in the constellation Scorpius. It is very close to the brighter, larger, and more colorful Rho Ophiuchi molecular cloud complex. This object is best photographed in the summer and is a good challenge for advanced astrophotographers.

Some equipment issues made acquiring this target much more difficult than it needed to be, and I had to spend several nights on it under dark skies. I did my best to process the data to the best of my abilities, and was able to get a pretty good overall image!

How did it turn out? find out below!

Object Designation: IC 4592

Also known as: The Blue Horsehead Nebula

Constellation: Scorpius

Object Type: Reflection Nebula

Distance: 420 light-years away

Magnitude: Unknown

Discovered in: 1771

IC 4601 Astrophotography in the Blue Horsehead Nebula
Crop on IC 4601

One of the most beautiful aspects of the Blue Horsehead Nebula is a second, much smaller nebula that lies near the ear of the horse.

IC 4601, which you can see on the left, is another blue reflection nebula that is illuminated by two binary blue giant stars.

IC 4601's colors really pop out with vibrant blue against the dark interstellar clouds that constitute the neck of the horse.

Packing up the telescope during Sunrise at Death Valley
Packing up the telescope during Sunrise at Death Valley

I imaged this object when I went on an unplanned Death Valley solo trip, (watch me get my car stuck in the sand, meet a scorpion, and image this object on YouTube!). The first night was a complete failure, as one of my cables was not cooperating and gave me corrupted images. I was able to image the nebula for less than three hours on the second night, after fixing my cable issue.

I imaged this target for a third night, which went really well, allowing me to add more hours to the data and total 12 hours!

Below is our final image of the Blue Horsehead Nebula. We are happy with the result, although it is extremely frustrating to know that the first night was completely ruined by a bad cable, and I am currently debating whether I should keep adding data to this image or not... Well, stick around and you'll find out!

The Blue Horsehead - 12 hours of exposure time from Death Valley, CA


Camera: QHY600C

Telescope: Meade 70mm APO

Mount: Astro-Physics Mach1

Guiding: ZWO ASI 290MM Mini

Processing: Pixinsight


Total Exposure Time: 12 hours

Exposure Time per frame: 10 minutes

Filters: N/A

Gain: 26


How to Find IC 4592

How to find the Blue Horsehead Nebula in the constellation Scorpius, map

Finding the Blue Horsehead Nebula is difficult visually, but very simple if you use a DSLR camera and a lens.

IC 4592 is located in Scorpius, a constellation that does not rise very high for northern observers. The good thing is that it lies very close to the bright Rho Ophiuchi cloud complex. If you cannot see Rho Ophiuchi, or are not sure how to find it, simply look for the bright orange star Antares.

wide-field milky way with rho ophiuchi and blue horsehead nebula

Antares is one of the stars that give the gases in Rho Ophiuchi their color, so if you are looking at Antares, you are also by definition looking at Rho Ophiuchi! To find the Blue Horsehead Nebula from there, hop North to the next bright star in Scorpius, Nu Scorpii (also known as "Jabbah" meaning "forehead" of the scorpion). Jabbah is the main star illuminating the Blue Horsehead Nebula. In our image at the top of this post, Jabbah is the star visible near the center/left area that makes up the eye of the horse.


Processing the Blue Horsehead Nebula

Processing IC 4592 was not easy. A fair amount of masks had to be used in order to bring all that dark nebulosity out without blowing up the bright blue gases near each of the bright stars. The main challenge was to be able to get as much dark gas as possible to form the entire horse's head and keep the noise levels low. The fact that this image was only 2.8 hours of total exposure did not help when it came to noise reduction.

The image below shows what a single shot of 10 minutes looks like. The shape of the horse's head can easily be seen, including some of the dark nebulosity on the right side. This image has been debayered, the shape of the object was much less obvious when the image appeared in black & gray on the laptop!

Blue Horsehead Nebula: Single 10-minute shot (left) and first attempt at processing (right)

If you are interested in learning how I process all our images, you can access our PixInsight workflow, which contains written lessons, walkthrough tutorial videos, our custom pre-sets and even raw data HERE.


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Final Thoughts

The Blue Horsehead Nebula is truly a magnificent object! It is difficult to capture, and also difficult to process, making it a rarely photographed target. It is also so close to the brighter and better-known Rho Ophiuchi that it is most of the time overlooked. We love the Blue Horsehead Nebula and would love to one day capture a full mosaic that will include both the Horse and Rho Ophiuchi.

Have you captured the Blue Horsehead Nebula? Attach your image in the comments and let us know your acquisition details!

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Clear Skies,

Galactic Hunter

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