GREAT RIFT

in astronomy, a complex of dark nebulae that seems to divide the bright clouds of the Milky Way Galaxy lengthwise through about one-third of their extent. From the constellation Cygnus, the rift reaches through Aquila and Sagittarius, where the centre of the Galaxy lies hidden behind it, to Centaurus. The clouds of dark material making up the Great Rift are several thousand light-years from the Earth.