Dark nebulae are dense clouds of interstellar gas and dust that block the light of stars or glowing nebulae behind them. They appear in the sky as dark, silhouette-like regions set against brighter backgrounds. Astronomically, dark nebulae are primarily composed of cold molecular hydrogen and dust particles. While the dust accounts for only about one percent of their mass, it is responsible for the obstruction of light. The temperatures in dark nebulae are extremely low, often around 10 Kelvin, which virtually eliminates thermal emission. The density of these nebulae varies greatly but typically ranges from a few hundred to several million molecules per cubic centimeter.
Dark nebulae are commonly found in the plane of the Milky Way and are closely associated with star-forming regions such as the Orion Molecular Cloud Complex. They can vary significantly in size, from small, compact globules like Bok globules to vast structures such as the famous Horsehead Nebula. Their distances typically span from several hundred to thousands of light-years. These nebulae play a critical role in astronomy, as they are often the birthplaces of new stars. In their dense cores, gas collapses under gravitational forces, leading to the formation of protostars.
Barnard 33 – Horsehead Nebula
The Horsehead Nebula, a dark nebula located in the constellation Orion approximately 1,500 light-years away from Earth, is best observed during its annual culmination at astronomical midnight mid December ...
