Horsehead Nebula
What is Horsehead Nebula?
Nebulae· Distance 1,375 ly. A cold cloud of dust just below Alnitak, the eastern star of Orion's Belt. Against a glowing red background it shows as the dark shape of a horse's head. It is famous in photos but very hard to see by eye.
📍 Visible from where you are right now — computed in your browser
Distance and scale
| Distance | ~1,375 ly |
|---|---|
| Size | ~3.5 ly tall |
| Type | dark nebula |
| Constellation | Orion |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Barnard 33: the light behind the Horsehead's dark shadow
The Horsehead's formal name is Barnard 33. It is number 33 in a list of dark objects published in 1919 by the American astronomer Edward Emerson Barnard. Barnard used photographs to show that the dark gaps scattered through the Milky Way are not empty holes without stars. They are clouds of dust blocking the starlight behind them. The Horsehead is the best-known example of such a dust cloud.
The red background behind the Horsehead is lit not by Alnitak but by Sigma Orionis, a group of hot stars to its south-west. Their ultraviolet light makes the hydrogen cloud behind the Horsehead glow. The Horsehead shows up so well in photos thanks to filters that let through only the red light given off by hydrogen. With such a filter the bright background stands out and the dark shape becomes sharper, so even a small telescope and camera can capture it after a few hours of collecting light.
The nebula in depth
The Horsehead Nebula does not shine on its own. It is a dark nebula that blocks the light behind it. Behind it is IC 434, a cloud of gas that glows red. This red cloud lights the scene from behind like a backdrop, and in front of it stands a cold pillar of dust about 3.5 light-years tall. The dust blocks the light and makes the dark silhouette of a horse's head. It is about 1,375 light-years away.
This dust cloud is part of a huge cloud of molecules that spreads across Orion. Inside, hydrogen molecules and dust are packed so tightly that starlight cannot get through. Williamina Fleming of Harvard Observatory first spotted it on a photographic plate in 1888. In 2013 the Hubble Space Telescope looked inside the dark shape using infrared light and revealed the cloud's 3-D structure.
In 2024 the James Webb Space Telescope took a very detailed picture of the top of the cloud, the part that forms the horse's mane. It shows the edge of the cloud splitting into thin threads as strong light from nearby stars wears it away. At the rate it is being worn down, the Horsehead is expected to break up and disappear in about five million years.
Frequently asked
- How far is Horsehead Nebula from Earth?
- The distance of Horsehead Nebula is ~1,375 ly.
- What kind of object is Horsehead Nebula?
- Horsehead Nebula is a dark nebula.
- In one line, what is Horsehead Nebula?
- Nebulae — A cold cloud of dust just below Alnitak, the eastern star of Orion's Belt.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.