Dark nebulae are dense clouds of gas and dust in space that block light from stars and other celestial objects behind them. They are often seen as dark patches against the brighter background of the Milky Way or other galaxies. These nebulae are important for star formation, as they provide the material needed for new stars to develop. These clouds can vary in size and shape, with some being small and compact while others stretch over vast areas. Dark nebulae are often associated with regions of active star formation, where the gravitational pull of the dust and gas can lead to the birth of new stars and planetary systems.