"A dark nebula is an interstellar cloud of cosmic dust that's so dense it absorbs, scatters and blocks visible light, making it appear inky black when viewed against the starry cosmos.Famous examples of a dark
nebula include the Coalsack Nebula, the
Horsehead Nebula and the Snake Nebula.Many dark nebulae are known as Barnard objects and are catalogued using the 'Barnard' designation followed by a number, like Barnard 363 (below).These are named after Edward Emerson Barnard, an American astronomer who published a record of dark nebulae known as the Barnard Catalogue in 1919, and an extended list posthumously in 1927.Dark nebulae are irregular in shape, unlike certain kinds of nebulae like
planetary nebulae, which generally have a spherical appearance.While dark nebulae may seem like foreboding, lifeless cosmic objects, in actual fact many of them are active regions where hydrogen molecules form and
stars are born.These stars are often hidden from optical light due to the density of the dark nebula in which they're born, but radio and infrared telescopes allow astronomers to peer through the cosmic dust and get a closer look at the star formation occurring within.A dark nebula may be the dense core of a Giant Molecular Cloud a million times more massive than the Sun, or they could take the form of compact molecular clouds known as Bok Globules, just 2,000 times the mass of the Sun.Bok globules are a type of dark nebula named after the Dutch-American astronomer Bart Bok, and are thought to be the precursor to protostars, just waiting to gain enough mass that they collapse, igniting the process of star formation.
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source:
https://www.skyatnightmagazine.com/astrophotography/nebulae/dark-nebula
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