Magellanic Clouds
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The two Magellanic Clouds (or Nubeculae Magellani[1]) are irregular dwarf galaxies, which are members of our Local Group of galaxies. Once they were thought to be orbiting our Milky Way galaxy. However, new research seems to indicate that this is not the case.[2][3] The two galaxies are:
- Large Magellanic Cloud (LMC)
- Small Magellanic Cloud (SMC)
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[edit] History
The Magellanic Clouds have been known since the earliest times by the ancient Middle Eastern peoples. The first preserved mention of the Large Magellanic Cloud was by Persian astronomer Al Sufi, who in 964, in his Book of Fixed Stars, calls it al-Bakr, meaning "the White Ox", of the southern Arabs, and points out that while invisible from Northern Arabia and Baghdad, this object is visible from the strait of Bab el Mandeb, at 12°15' Northern latitude.[1]
In Europe, the Clouds were first observed by Italian Peter Martyr and Andreas Corsali at the end of the 15 century. Subsequently, they were reported by Antonio Pigafetta for the expedition of Ferdinand Magellan during the circumnavigation in 1519–1522.[1] However, naming the clouds after Magellan did not become widespread until much later. In Bayer's Uranometria they are designated as NVBECVLA MAIOR[4] and NVBECVLA MINOR[4]; even in French astronomer Lacaille's 1756 star map, they are designated as le Grand Nuage[5] and le Petit Nuage.[5] (i.e. the "Large Cloud" and the "Small Cloud", in Latin or French).
[edit] Characteristics
The Large Magellanic Cloud and its neighbor and relative, the Small Magellanic Cloud, are conspicuous objects in the southern hemisphere, looking like separated pieces of the Milky Way to the naked eye. Roughly 21° apart in the night sky, the true distance between them is roughly 75,000 light-years. Until the discovery of the Sagittarius Dwarf Elliptical Galaxy in 1994, they were the closest known galaxies to our own.
Observation and theoretical evidence suggest that the Magellanic Clouds have both been greatly distorted by tidal interaction with the Milky Way as they travel close to it. Streams of neutral hydrogen connect them to the Milky Way and to each other, and both resemble disrupted barred spiral galaxies. (Zeilik) Their gravity has affected the Milky Way as well, distorting the outer parts of the galactic disk. (Chaisson and McMillan)
The Magellanic Clouds' radial velocity and proper velocity were recently accurately measured by a team from the Harvard-Smithsonian Center for Astrophysics to produce a 3-D velocity measurement that clocked their passage through the Milky Way galaxy in excess of 480km/s (300 miles per second) using input from Hubble Telescope. This unusually high velocity seems to imply that they are in fact not bound to the Milky Way, and many of the presumed effects of the Magellanic Clouds have to be revised.[6]
Aside from their different structure and lower mass, they differ from our Galaxy in two major ways. First, they are gas-rich; a higher fraction of their mass is hydrogen and helium compared to the Milky Way.[7] They are also more metal-poor than the Milky Way; the youngest stars in the LMC and SMC have a metallicity of 0.5 and 0.25 times solar, respectively.[8] Both are noted for their nebulae and young stellar populations, but as in our own Galaxy their stars range from the very young to the very old, indicating a long stellar formation history.(Chaisson and McMillan)
The Large Magellanic Cloud was host galaxy to a supernova (SN 1987A), the brightest observed in over three centuries.
[edit] In fiction
- See Galaxies in fiction.
[edit] See also
[edit] References
- ^ a b c Allen, R. H., (1963). Star Names: Their Lore and Meaning (rep. ed.). New York, NY: Dover Publications Inc., pp. 294-295.
- ^ http://news.bbc.co.uk/1/hi/sci/tech/6249421.stm News.bbc.co.uk Retrieved on 2007-05-31
- ^ http://www.cfa.harvard.edu/press/2007/pr200722.html Harvard presse release Retrieved on 2007-09-22
- ^ a b Bayer, J., (1661) Uranometria, pl. Aaa (49). (US Naval Observatory,Retrieved on 2009-09-05)
- ^ a b de Lacaille, N. L., (1756) "Planisphere contenant les Constellations Celestes", Memoires Academie Royale des Sciences pour 1752. (Linda Hall Liblary,Retrieved on 2009-09-05)
- ^ http://www.centauri-dreams.org/?p=1468 See second Paragraph below inserted picture.
- ^ http://home.insightbb.com/~lasweb/lessons/magellanic.htm Home.insightbb.com Retrieved on 2007-05-31
- ^ http://aa.springer.de/papers/8336003/2300925/sc6.htm Aa.springer.de Retrieved on 2007-05-31
- Eric Chaisson and Steve McMillan, Astronomy Today (Englewood Cliffs: Prentice-Hall, Inc., 1993), p. 550.
- Michael Zeilik, Conceptual Astronomy (New York: John Wiley & Sons, Inc., 1993), pp. 357–8.
[edit] External links
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