NGC/IC Objects

B33 "Horsehead Nebula": Dark Nebula (Orion) RA: 05h 40.7m / DEC: -02° 27'.0
Instrument: 10-inch Starfinder

The Horsehead nebula is a real deep-sky challenge. Good optics, solid observing skills and excellent conditions are required to meet the challenge. You might be surprised to hear that large aperture is not required. The Horsehead is a dark nebula (B33) seen in the foreground of a delicate emission nebula (IC 434). IC 434 is not very bright so the contrast between it and the Horsehead is quite low. As long as the optics, seeing and transparency are good, a 6-inch aperture is up to the task.

The Horsehead is located 31' south of Alnitak, the easternmost star in Orion's belt. NGC 2024, an emission nebula with a wide dark channel running north-south through the middle, should be visible about 15' east of Alnitak. This is the Flame nebula and is sometimes mistaken for the Horsehead. If you can't see the Flame nebula, don't even bother with the Horsehead. Both Alnitak and the Flame nebula are outside the field of view in the sketch at left, which presents an 82X view in my 10-inch Newtonian.

Twenty-three arc minutes southeast of Alnitak, NGC 2023 is visible as an island of nebulosity surrounding 7.8 magnitude HD 37903. IC 434, a corridor of north-south running nebulosity is just barely visible west of NGC 2023. The Horsehead is located 15' southwest of HD 37903. It appears as a notch of darker sky within IC 434. To say the Horsehead is subtle would be a gross understatement. The Horsehead is framed by a handful of 12th magnitude GSC stars forming a "stair step" asterism. You can use these to identify the field.

When you go after the Horsehead, look first for the Flame nebula and NGC 2023. If they're not visible, the Horsehead won't be. Then look for IC 434. Same deal, if it's not seen, don't bother trying for the Horsehead. Then, look for those five stars that frame the Horsehead. Once you know where to look, finding an object becomes much easier. An H-beta filter will enhance IC 434 and make the Horsehead easier to detect. Good luck.

Instrument: 18-inch Obsession

The observation at left was made in January 2006, 10 years after the first. Since getting the 18-inch Obsession in September 2004, I've never had a night when the Horsehead wasn't visible when I turned the big Dob in its direction. But on this night, the views were truly stunning. Even unfiltered, the inky black form of B33 was obvious at 109X (22-mm Nagler Type 4 w/ Paracorr). Surprisingly, it was an easy detection in my friend's 6-inch, f/8 Newtonian. I suspect a quality 4-inch refractor may have been up to the task on this night.

My drawing represents a combination of two views. The first was unfiltered to record the stars. The second was with a Lumicon hydrogen-beta (H-beta) filter in place to record the full glory of the B33/IC 434 complex. Some 60 stars frame the view. Among these are the three 12th magnitude embers that crown the dark nebula, which is nearly centered. 7.5 magnitude HD 37805 blazes away nearly 10' north of B33. HD 37903 is enmeshed within NGC 2023 just inside the northeast field boundary. 6.2 magnitude HD 37744 marks the southern limit of the field. The horsehead cuts into IC 434 along the nebula's eastern edge. It is distinctively darker than the surrounding sky. It has a genuine inky blackness, as if someone has carelessly left the tip of their quill too long against the sky. The back of the horse's neck, head, brow, and snout are all discerned. This is as much detail as I've ever seen in the Horsehead.

Sharpless 2-240 Hickson 16


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Revised: December 4, 2005 [WDF]