# Dark nebula

Also called: Barnard object, absorption nebula.

A dense cloud of dust seen in silhouette against the stars or glowing gas behind it.

Dark nebulae are holes that aren't holes: thick dust blocks the light of everything behind them. The Coalsack, next to the Southern Cross, is visible to the naked eye; the Horsehead Nebula (Barnard 33) is a dark pillar against the faint glow of IC 434.

E. E. Barnard catalogued hundreds of them in the early 1900s — hence names like B 33.

**At the eyepiece:** The Horsehead is a famous challenge: it needs a dark sky, at least 8 inches of aperture and an H-beta [nebula filter](https://astropilot.space/glossary/nebula-filter) to darken the sky around IC 434.

**Examples:** [B33](https://astropilot.space/object/B33.md), [C99](https://astropilot.space/object/C99.md)

**Related:** [Nebula](https://astropilot.space/glossary/nebula.md), [Emission nebula](https://astropilot.space/glossary/emission-nebula.md), [Milky Way](https://astropilot.space/glossary/milky-way.md)

From the AstroPilot astronomy glossary: https://astropilot.space/glossary/dark-nebula