Great clouds of gas and dust, called nebulae, extend across space. Bight clouds are limited regions stimulated to shine by the light of nearby hot stars. An example is the faint patch of light just discernible in the sword of the constellation Orion. In reality this is a nebula about 15 light years across, the birthplace of thousands of new stars.
More extensive are the dark nebulae. The bulk of these is transparent gas, but the dust in them blocks the light from stars beyond. The dark “lanes” that we seen in the Milky Way are actually dust clouds blocking our view of the piled up banks of stars lying beyond and preventing us from seeing to the center of the galaxy, 30,000 light years away.