RigTonightHow to photograph the Horsehead and Flame nebulae
The Horsehead Nebula is one of the most recognisable shapes in the sky, and one of the most satisfying targets to capture for the first time. The horse's head itself (Barnard 33) is a cloud of cold, dark dust. You see it only in silhouette, against the red glow of the hydrogen behind it, a sheet of emission nebula called IC 434. Just next door is the Flame Nebula (NGC 2024), a bright, orange-and-brown cloud split by dark dust lanes.
When and where
- Position: RA 5h 41m, Dec −2° 27′, just south of Alnitak, the easternmost star of Orion's belt.
- Season: best from December to March in the evening. Like the Orion Nebula, it's near the celestial equator and visible from almost everywhere.
- Neighbours: the Orion Nebula is about 3° to the south. At short focal lengths you can get both in one frame.
Framing
The horse's head itself is small, only about 8′ × 6′, but the region around it (IC 434, the Flame and Alnitak) covers about 90′ × 60′.
| Focal length (APS-C sensor) | What you get |
|---|---|
| 135–250 mm | The Horsehead, Flame, belt stars and the Orion Nebula together |
| 400–600 mm | The Horsehead and Flame together: the classic frame |
| 800–1200 mm | The Horsehead filling the frame |
| 1500 mm and up | Close-up detail in the head and the bright rim behind it |
Filters
The glowing backdrop of IC 434 is hydrogen-alpha emission, so:
- Hα is the key filter. With a mono camera, Hα shows the horse sharply against a bright red background, even from the suburbs and under the moon.
- Dual-band on a colour camera works well for the same reason.
- Broadband (or RGB added to Hα) brings out the Flame's warm colours, the small blue reflection nebula NGC 2023 beside the horse, and natural star colours. It needs a darker sky.
Dealing with Alnitak
Alnitak, at magnitude 1.8, sits right next to the Flame Nebula, and it can cause large halos, reflections and diffraction spikes:
- Frame so Alnitak sits near an edge of the frame, or just outside it at longer focal lengths.
- Filters with poor coatings can add rings around it; good narrowband filters and refractors keep it tidy.
- Keep subs short enough that Alnitak's halo doesn't swamp the Flame. Around 120–300 seconds through narrowband, less with broadband.
Exposure
The horse is faint. Plan on 3–5 hours of Hα, or longer with a dual-band filter on a colour camera. The dark head only stands out once the background glow is smooth and well exposed, and it keeps getting better with more time.
Example rigs
RigTonight's Targets tab draws your exact camera frame on the Horsehead region, so you can see where Alnitak falls before you start, and the Tonight tab shows when it's highest from your site.