Can you locate and capture the Horsehead Nebula with a camera or a smartphone?
Orion, the Hunter remains prominent through February and this is a great time to try for what used to be regarded as a difficult photographic target, the Horsehead Nebula, B33. In modern times, highly sensitive camera sensors have made it less tricky and if you’ve never attempted it before, this is a great time to try. If you have captured it in the past, we’ve got an extended challenge for you too.
The Horsehead is a dark nebula, a protrusion of gas which creates a silhouette in front of a glowing curtain of emission nebula IC 434. The curtain runs south of Alnitak (Zeta (ζ) Orionis). From Alnitak, locate mag. +3.8 Sigma (σ) Orionis 0.8˚ to the southwest. Now look 0.5˚ to the east-southeast where you’ll find mag. +6.2 HIP 26713 with mag. +6.4 HIP 26820, 0.3˚ further to the east. Both faint stars are distinctive in the region and identifiable. IC434 runs from just south of Alnitak towards HIP 26820. The Horsehead is midway between Alnitak and HIP 26820.
In order to capture it you’ll need a camera set up on an equatorial, polaraligned, tracking mount. This could be a camera on its own or one attached to a telescope. A field of view of at least 2˚ is recommended. Using a full-frame DSLR camera requires a focal length of less than 1,000mm, while a camera with an APS-C sensor requires a focal length of less than 600mm.
Focus accurately and frame your shot to include both Alnitak and HIP 26820. Set your camera to a mid-range ISO and take as long an exposure as your mount will allow without star trailing. If you’re not sure what this limit is, use the ‘bracket exposure’ technique, where you take a series of test shots – with exposures of 30 seconds, 60 seconds and 90 seconds etc – until you see signs that the stars are starting to trail.
Taking multiple shots along with dark frames etc, will allow you to produce a better result, but if you’re impatient and want to see what’s there, load your longest exposure into a graphics editor, open adjustment levels and move the two extreme markers so they sit at the data peak’s start and end. If successful, the Horsehead silhouette will become obvious. The next step is to improve on the result.
If you’re an old hand at imaging the Horsehead with a camera, you could try the further challenge of capturing it with a smartphone. It’s possible with a bright object such as M42, but the Horsehead may be beyond this method of capture.