In astronomy

Astronomy

Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...

, the Great Rift (sometimes called the Dark Rift or, less commonly, Dark River) is a series of overlapping, non-luminous, molecular dust clouds

Cosmic dust

Cosmic dust is a type of dust composed of particles in space which are a few molecules to 0.1 µm in size. Cosmic dust can be further distinguished by its astronomical location; for example: intergalactic dust, interstellar dust, interplanetary dust and circumplanetary dust .In our own Solar...

 that are located between the Solar System

Solar System

The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...

 and the Sagittarius Arm

Sagittarius Arm

The Carina–Sagittarius Arm is generally thought to be a minor spiral arm of our home galaxy, the Milky Way. Each spiral arm is a long, diffuse curving streamer of stars that radiates out from the galactic center...

 of the Milky Way Galaxy at a distance of about 100 parsec

Parsec

The parsec is a unit of length used in astronomy. It is about 3.26 light-years, or just under 31 trillion kilometres ....

s or about 300 light years (2×10¹⁵ miles or 3×10¹⁵ kilometers) from Earth. The clouds are estimated to contain about 1 million solar mass

Solar mass

The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...

es of plasma

Plasma (physics)

In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...

 and dust.

To the naked eye, the Great Rift appears as a dark lane that divides the bright band of the Milky Way

Milky Way

The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...

 lengthwise, through about one-third of its extent, and is flanked by lanes of numerous stars.

Starting at the constellation of Cygnus

Cygnus (constellation)

Cygnus is a northern constellation lying on the plane of the Milky Way. Its name is the Latinized Hellenic word for swan. One of the most recognizable constellations of the northern summer and autumn, it features a prominent asterism known as the Northern Cross...

, where it is known as the Cygnus Rift or Northern Coalsack, the Great Rift stretches to Aquila

Aquila (constellation)

Aquila is a stellar constellation. Its name is Latin for 'eagle' and it is commonly represented as such. In mythology, Aquila was owned by the Roman god Jupiter and performed many tasks for him....

; to Ophiuchus

Ophiuchus

Ophiuchus is a large constellation located around the celestial equator. Its name is from the Greek "serpent-bearer", and it is commonly represented as a man grasping the snake that is represented by the constellation Serpens. Ophiuchus was one of the 48 constellations listed by the 2nd-century...

, where it broadens out; to Sagittarius

Sagittarius (constellation)

Sagittarius is a constellation of the zodiac, the one containing the galactic center. Its name is Latin for the archer, and its symbol is , a stylized arrow. Sagittarius is commonly represented as a centaur drawing a bow...

, where it obscures the Galactic Center

Galactic Center

The Galactic Center is the rotational center of the Milky Way galaxy. It is located at a distance of 8.33±0.35 kpc from the Earth in the direction of the constellations Sagittarius, Ophiuchus, and Scorpius where the Milky Way appears brightest...

; and finally to Centaurus

Centaurus

Centaurus is a bright constellation in the southern sky. One of the largest constellations, Centaurus was included among the 48 constellations listed by the 2nd century astronomer Ptolemy, and it remains one of the 88 modern constellations.-Stars:...

. One of the most important regions it obscures is the Cygnus OB2 association

Cygnus OB2

Cygnus OB2 is one of the largest young clusters of stars in our Galaxy, and home to some of the most massive stars known, including Cyg OB2 #8 and Cyg OB2 #12, one of the most luminous stars known. The region is embedded within a wider region of star formation known as Cygnus X, which is one of the...

, a large cluster

Star cluster

Star clusters or star clouds are groups of stars. Two types of star clusters can be distinguished: globular clusters are tight groups of hundreds of thousands of very old stars which are gravitationally bound, while open clusters, more loosely clustered groups of stars, generally contain less than...

 of young stars and one of the largest regions of star formation near the Earth. A similar dark band can be seen in edge-on distant galaxies, such as NGC 891

NGC 891

NGC 891 is an edge-on unbarred spiral galaxy about 30 million light-years away in the constellation Andromeda. It was discovered by William Herschel on October 6 1784. The galaxy is a member of the NGC 1023 group of galaxies in the Local Supercluster...

 in Andromeda

Andromeda (constellation)

Andromeda is a constellation in the northern sky. It is named after Andromeda, the princess in the Greek legend of Perseus who was chained to a rock to be eaten by the sea monster Cetus...

.