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Great Rift

Dark Rift, Dark River, Dark Side

Proper NamesDark Rift, Dark River, Dark Side, Great Rift
Messier NumberNone
NGC/IC NumberNone
Constellations (east to west)Cygnus, Sagitta, Aquila, Serpens, Scutum, Sagittarius, Ophiuchus, Scorpius, Ara, Norma, Circinus, Centaurus
Right Ascensionc. 13h 30m to 20h 45m
Declinationc. -63° to +45°
Distancec. 300 light years
c. 100 parsecs
(at closest approach, highly variable)
Optimum VisibilityApril to August (the southern parts of the Rift are usually visible in southern latitudes)
NotesA narrow band of dark obscuring matter that runs along the Milky Way for some 130°, or just over a third of its entire circuit of the sky. The Rift blocks light from the Galaxy beyond, including the regions around the Galactic Core in Sagittarius.

A large and prominent feature of the Milky Way in the sky, the Great Rift forms a dark thread that divides the main band of the Milky Way into two separate strands for about a third of its length. This feature is not truly a 'rift', but a string of dark clouds of dust stretching along the plane of the Galaxy. These immense clouds are some hundreds of light years from the Solar System, and together they obscure the brighter disc and core of the Galaxy that extend out for thousands of light years beyond.

The Rift is not uniformly dark, and examined in detail it reveals rich patterns of internal structure, with tendrils of matter stretching away from the central mass. Structures of this kind are not unique to the Milky Way, and several other spiral galaxies can be observed to show similar patterning, with lanes of dark dust accumulating along their central planes or around their rims.

A detailed view of the Great Rift as it passes through western Sagittarius. This marks the general direction of the Galaxy's core, though the nucleus itself is entirely obscured by the dust of the Rift. The two lighter areas within the dark lane are nebulae: the larger of the two is the Lagoon Nebula, M8, while the smaller object to the north is the Trifid Nebula, M20. Imagery provided by Aladin sky atlas

In the sky, the Milky Way's Great Rift begins near Deneb in Cygnus, where a particularly dense patch of dust forms a segment known as the Cygnus Rift. From there it stretches southward and westward through Vulpecula, Sagitta, Aquila and Serpens. At this point it enters Sagittarius, and its clouds obscure the Galactic Nucleus that lies within that constellation. From Sagittarius, the Rift runs on through Scorpius and the minor constellations of Ara, Norma and Circinus until it reaches its end in the vicinity of the star Alpha Centauri.


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