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Sadr Region

Gamma Cygni Nebula, Butterfly Nebula, IC 1318

Proper NamesSadr Region, Gamma Cygni Nebula, Butterfly Nebula
Messier NumberNone
NGC/IC NumberIC 1318
Right Ascension20h 19m 0s
Declination+40° 20' 0"
Distancec.3,500 light years
c.1,100 parsecs
(highly approximate)
MagnitudeApparent: +10.00
Absolute: +1.69
DimensionsApparent: 3° 30' x 2°
Actual: at least 100 light years
Optimum VisibilityAugust

A vast complex of emission clouds and dark clumps and strings of matter in the heart of the constellation Cygnus. This nebulous region creates a dramatic backdrop to the star Sadr (also called Sadir or Gamma Cygni) that forms the central point of the asterism within Cygnus known as the Northern Cross. Sadr itself is not part of the Sadr Region but lies on a direct line between the Solar System and the more distant nebula complex.

The distance to the nebula is not known with certainty, but it probably lies some 2,000 to 5,000 light years from the Sun. This means that the entire sprawling region is at least a hundred light years across, and may, depending on its true distance, approach three hundred light years from side to side. It has a mottled appearance, with bright pink-orange areas of ionised hydrogen being obscured in places by a tracery of dark dust clouds and lanes.

A view of the central regions of the extensive Sadr Region. The bright star to the east (left) of centre in this view is Sadr itself, the foreground star from which the region takes its name. Visible within the nebula are two young open clusters, Collinder 420 (to the northeast of Sadr) and Collinder 419 (to the northwest). Imagery provided by Aladin sky atlas

Three brighter areas of the Sadr Region stand out from the main mass, and these are given individual designations. IC 1318A forms a distinct northern lobe in the north of the Region, while IC 1318B and IC 1318C lie to the south, closer to the star Sadr in the sky. IC 1318B and IC 1318C form a nearly symmetrical pattern divided by a dark lane, and are sometimes jointly known as the Butterfly Nebula (not to be confused with C69, the Bug Nebula in Scorpius, which is also sometimes known as the 'Butterfly Nebula').

As well as being densely nebulous, the Sadr Region is also rich in open clusters, newly hatched groups of stars scattered throughout this star-forming region. Most notable among these is Collinder 420 (or NGC 6910), which appears close to Sadr in the sky near the IC 1318B zone of the Region. A little farther away in the sky is an even more prominent cluster, M29. While not now part of the Sadr Region, the M29 cluster is thought to have had its origins within that huge accumulation the star-forming material.


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