Dark nebulae are the result of cool clouds of gas that are neither ionized nor illuminated, though they are actually physically quite similar to reflection nebulae.
Dark nebulae can be seen as voids in the background star field, or can be located along the line of sight to a nebula. In general, they are perhaps among the most difficult deep sky objects to hunt, as their surroundings must first be readily apparent. Dark skies are often crucial for their detection.
- B33 (Horsehead Nebula), in Orion
- B86 (Ink Spot Nebula), in Sagittarius
- B92, in Sagittarius
- B168, in Cygnus