The Horsehead Nebula In Hydrogen Alpha

I had an unexpected clear night recently. So I decided to take the Astronomik Ha 12nm Clip In Filter for a road sky space test. Pointing the telescope towards Orion, I decided to begin gathering data on The Horsehead Nebula.

The Horsehead Nebula

Otherwise known as Barnard 33, this dark nebula gets its name by the striking resemblance to that of a horse’s head. Often (almost always) photographed with it is the reflection nebula NGC 2023. The Horsehead Nebula is a popular winter time target and as such the perfect time to photograph it is late November to January.

Being partly an emission nebula, one popular trick is imaging this nebula in Hydrogen Alpha. Hydrogen Alpha is a narrowband wavelength of light that only allows light from that gas to pass through.The Astronomik Hydrogen Alpha Filter Is Used To Isolate The Hydrogen Alpha Wavelength.

I was able to capture this wavelength due to the generosity of The Widescreen Centre in loaning me the filter for review. The Astronomik 12nm Hydrogen Alpha Clip-In Filter is a heavy weight filter known for being really useful and good with DSLR cameras. So it was perfect for me and my modified Canon 600D.

Alnitak

We can’t talk about the Horsehead Nebula without the Shire Horse in the room – Alnitak. This bright Class O star within Orion’s Belt makes shooting the Horsehead Nebula (and by extension the Flame Nebula) difficult. We need nice long exposures to capture the beauty of the Horsehead. Yet, with too much time, Alnitak decides to shine brighter and brighter.

I’ve seen the Horsehead Nebula cited as Magnitude 6.8. Alnitak, however, is magnitude 2. Making it much brighter.

We can help control Alnitak using hydrogen alpha data. One benefit of Ha data is making stars smaller. It won’t stop this bright star entirely. Just helps control it. Just another reason to love Ha data.

Exposures

As the Ha data is narrowband, and the Horsehead Nebula is pretty dark already (being a dark nebula, after all), selecting the correct exposure is a bit of trial and error.

With my Canon 600D, I didn’t want to go to ISO1600. It was certainly cold enough to be able to bump the ISO up, but I like to stay at 800 wherever possible (I’m also too lazy to shoot ISO1600 bias frames).

I tried 3 minutes at ISO 800, but I couldn’t see much data coming through. I mean, Alnitak still was there as an ever present beacon of light. But as for the actual hydrogen data I was trying to grab, not so much.

So instead I bumped up the exposures to 5 minutes long. A few test shots later and I had decided that I was happy with that length. Had this been the middle of summer I may have ended up going 3 minutes ISO 1600, just to stop exposing so long. (I did very long exposures with a DSLR mid summer this year and you can see how well that turned out in this video).

A Raw 5 Minute Exposure

The red tint is taken care of in post production after stacking. It’s red because Hydrogen Alpha is located on the red part of the spectrum up at 656nm.

The Horsehead Nebula In Hydrogen Alpha

So with all considerations taken into account, I carried on that night with 5 minute sub exposures. I ultimately ended up with 31 x 300s of exposures for a hydrogen alpha image with just over 2 and a half hours of integration time.

To this I will add RGB data and combine into a HaRGB composite image. I’ve done HaRGB composites before with my California Nebula photo. This nebula is striking as it is in monochrome as it shows so much contrast and detail. But I think its true beauty will come clear once the composite has been made.

Summary

Whilst this is a well imaged nebula by so many astrophotographers, I don’t have one in my own portfolio. It’s such a striking and iconic nebula. Everyone knows it, and I strive to have one of my own. The Ha data is a solid start that was able to be acquired whilst the Moon was out, with thanks to the Moonlight resisting nature of Ha filters.

This final image was stacked in Deep Sky Stacker and then processed quite minimally in Photoshop.

Again, one big shoutout to The Widescreen Centre for allowing me the ability to review this filter. That review should be out sooner than later – if the UK weather behaves itself.

Until then, keep looking up and keep them cameras clicking.

The Horsehead Nebula Presented In Hydrogen Alpha

 

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