Great Rift (astronomy)
In astronomy, the Great Rift (sometimes called the Dark Rift, or less commonly the Dark River), is an area of dark bands that appear to obscure the center of the Milky Way galaxy when seen from the earth. They are thought to be an aggregation of overlapping, non-luminous, molecular dust clouds that lie between the Solar System and the Sagittarius Arm of the galaxy. They form a dark lane through the starry path of the Milky Way which, seen from Earth, is a hazy band of white light, some 30° wide, arching across the night sky. These clouds are located about 800–1,000 parsecs (2,600–3,300 ly) from Earth. The clouds are estimated to contain about 1 million solar masses of plasma and dust.
Starting at the constellation of Cygnus, where it is known as the Cygnus Rift or Northern Coalsack, the Great Rift stretches to Aquila; to Ophiuchus, where it broadens out; to Sagittarius, where it obscures the Galactic Center; and finally to Centaurus. One of the most important regions it obscures is the Cygnus OB2 association, a large cluster of young stars and one of the largest regions of star formation near Earth. Similar dark rifts can be seen in many edge-on galaxies, such as NGC 891 in Andromeda and NGC 4565 (the Needle Galaxy) in Coma Berenices.
The dark areas obscuring the Milky Way were recognized by some ancient civilizations. In South America the Inca gave some patterns of darkness and stars names much as normal stellar constellations were, including a series of animals like llamas, a fox, toad, and so on, thought to be drinking from the "great river" (the Milky Way) and seen in silhouette.
The classical Greeks sometimes described the Great Rift as being the path of devastation left by Phaeton, who tried to guide the chariot of Helios (the Sun god) across the sky and lost control, wreaking havoc before being struck down by a lightning bolt of Zeus.
Modern astronomy first began to notice the rift in the 18th century, but struggled to explain it until E. E. Barnard and Max Wolf in the early 20th century, who produced the currently accepted explanation after careful photographic study.
Of this, Barnard said:
|“||I did not at first believe in these dark obscuring masses. The proof was not conclusive. The increase of evidence, however, from my own photographs convinced me later, especially after investigating some of them visually, that many of these markings were not simply due to an actual want of stars but were really obscuring bodies nearer to us than the distant stars. — Astrophysical Journal (1919)||”|
Mysterious ring composed of very dense and cold gas and dust around the Galactic Center
- Green, Gregory M; Schlafly, Edward F; Finkbeiner, Douglas P; Rix, Hans-Walter; Martin, Nicolas; Burgett, William; Draper, Peter W; Flewelling, Heather; Hodapp, Klaus; Kaiser, Nicholas; Kudritzki, Rolf Peter; Magnier, Eugene; Metcalfe, Nigel; Price, Paul; Tonry, John; Wainscoat, Richard (2015). "A Three-Dimensional Map of Milky Way Dust". The Astrophysical Journal. 810: 25. arXiv:1507.01005. Bibcode:2015ApJ...810...25G. doi:10.1088/0004-637X/810/1/25.
- "Great Rift: Dark area in the Milky Way". EarthSky Communications. 2010. Retrieved 2010-06-15.
- Pitts, Sam. "NGC 891 Edge on Galaxy (HV19)". Sams Astro. Retrieved 2009-04-25.
- Dark Rift in the Milky Way
- The Northern Coalsack
- Paddle the Milky Way’s Dark River
- "The Great Rift". Encyclopædia Britannica Online. 2009. Retrieved 2009-04-25.
- "Great Rift". Sci-Tech Dictionary:. Retrieved 2009-04-25.
- Kaler, Jim. "The Milky Way - From STARS". University of Illinois at Urbana-Champaign. Department of Astronomy. pp. Maps 2 and 5. Retrieved 2009-04-25.
- Dark River, Wide Field by Rogelio Bernal Andreo, at APOD