Dark Horse (astronomy)
Dark Horse Nebula
|Observation data: J2000.0 epoch|
|Right ascension||17h 21m|
|Apparent magnitude (V)||–|
|Apparent dimensions (V)||10 degrees|
|Absolute magnitude (V)||–|
|Designations||Great Dark Horse|
The Dark Horse Nebula or Great Dark Horse (sometimes called The Prancing Horse) is a large dark nebula, which as seen from Earth, obscures part of the upper central bulge of the Milky Way. The Dark Horse lies in the equatorial constellation Ophiuchus (the Serpent Bearer), near its borders with the more famous constellations Scorpius and Sagittarius. It is a significant, visible feature of the Milky Way's Great Rift. It can only be seen from very dark places (places without light pollution) and places that do not have a lot of moisture in the atmosphere.
This region of dark nebulae is called Dark Horse because it resembles the side silhouette of a horse and appears dark as compared with the background glow of stars and star clouds. It is also known as "Great" because it is one of the largest (in apparent size) groups of dark nebulae in the sky.
The rear of The Great Dark Horse (its rump and hind legs), is also known as the Pipe Nebula, which itself carries the designation B77, B78, and B59. (The 'B' numbers reference entries in the Barnard Catalogue of dark nebulae.) The Snake Nebula (B72) is by comparison a small S-shaped nebula emerging from the west side of the northern part of the bowl of the Pipe (B77).
Barnard 68 is another named dark patch of molecular gas and dust appearing in the Dark Horse Nebula.