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Magellanic Clouds

 
Dictionary: Mag·el·lan·ic Clouds   (măj'ə-lăn'ĭk) pronunciation
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pl.n.
Two small, irregularly shaped galaxies that are the galaxies closest to the Milky Way and are faintly visible near the south celestial pole.

[After Ferdinand MAGELLAN.]


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Britannica Concise Encyclopedia: Magellanic Cloud
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Either of two irregular companion galaxies of the Milky Way Galaxy, named for Ferdinand Magellan, whose crew discovered them during the first voyage around the world. They share a gaseous envelope and lie about 22° apart in the sky near the southern celestial pole (see celestial sphere). They are visible to the unaided eye in the Southern Hemisphere but cannot be seen from northern latitudes. The Large Magellanic Cloud is more than 150,000 light-years from Earth; the Small Magellanic Cloud is roughly 200,000 light-years away. They are excellent laboratories for the study of the formation and evolution of stars.

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Sci-Tech Encyclopedia: Magellanic Clouds
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Two small, irregular galaxies that are close companions of the Milky Way Galaxy. Both are nearby galaxies that are located in the southern sky, not far from the south celestial pole. When viewed without a telescope, they resemble small sections of the Milky Way that might have drifted away from the main arc. The Large Magellanic Cloud (LMC) subtends an angular extent of about 5° in the sky, and the Small Magellanic Cloud (SMC) is about 3° across. Telescopic studies show, however, that each is really much larger than it appears. See also Milky Way Galaxy.

The Magellanic Clouds are rather small irregular-type galaxies. The Large Magellanic Cloud is at a distance of 160,000 light-years (1.5 × 1018 km or 9 × 1017 mi), and the Small Cloud is about 10% farther away. The explosion of Supernova 1987A in the Large Magellanic Cloud was seen in February 1987. The galaxies are satellites of the Milky Way Galaxy. See also Supernova.

It was shown in 1998, using Hubble Space Telescope measurements, that the oldest globular clusters in the Large Magellanic Cloud have the same ages as the oldest such clusters in the Milky Way Galaxy, indicating that both galaxies must have formed at nearly the same time. The Small Magellanic Cloud may have formed more recently, as no very old clusters have yet been identified among its several hundred star clusters. Both Magellanic Clouds have large numbers ofvery young stars, most of which are located in stellar associations, each ofwhich contains several hundred recently formed stars in loose aggregates about200 light-years (2 × 1015 km or 1.2 × 1015mi) across. See also Star clusters.

Both objects also are rich in gas, mostly neutral hydrogen gas. In certainareas the gas is heated by nearby bright stars, producing brilliant glowingnebulae. The brightest and biggest is the 30 Doradus nebula, one of the mostremarkable objects of the nearby universe, which includes a “nursery” forthe formation of supergiant stars. See also Interstellar matter; Nebula; Supergiant star.

 
Columbia Encyclopedia: Magellanic Clouds
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Magellanic Clouds (măj'əlăn'ĭk), two dwarf galaxies located in the far southern sky and visible to the unaided eye; they are classified as irregular because they show no definite symmetry or nucleus. The larger of the two, known as the Large Magellanic Cloud (LMC), is located mostly in the constellation Dorado; its angular diameter measures approximately 7°. The Small Cloud (SMC) is almost completely in the constellation Tucana, and measures approx. 4° in diameter. Both are nearly 160,000 light-years from the earth. They are part of the Local Group of galaxies, which includes our own galaxy (the Milky Way) and the Andromeda Galaxy, and are the nearest extragalactic objects. The Magellanic Clouds, named for the Portuguese navigator Magellan, were first studied in detail by Sir John Herschel in the 19th cent. While studying Cepheid variable stars in the SMC, Henrietta Leavitt discovered (1912) the period-luminosity relation. This relation offered a technique for measuring the distances of stars and galaxies. In Feb., 1987, Supernova 1987A erupted in the LMC. The first supernova visible without a telescope since 1604, this star gradually brightened over the next few months and remains under careful observation as it fades. The diffuse nebulae in both the LMC and the SMC appear to have fewer "metals" (elements heavier than helium); the deficiency is much more pronounced in the SMC.

Wikipedia: Magellanic Clouds
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The Large and Small Magellanic Clouds.

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:

Contents

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).

Characteristics

The Large Magellanic Cloud (LMC)
Part of the Small Magellanic Cloud (SMC)

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.

In fiction

See Galaxies in fiction.

See also

References

  1. ^ a b c Allen, R. H., (1963). Star Names: Their Lore and Meaning (rep. ed.). New York, NY: Dover Publications Inc. , pp. 294-295.
  2. ^ http://news.bbc.co.uk/1/hi/sci/tech/6249421.stm News.bbc.co.uk Retrieved on 2007-05-31
  3. ^ http://www.cfa.harvard.edu/press/2007/pr200722.html Harvard presse release Retrieved on 2007-09-22
  4. ^ a b Bayer, J., (1661) Uranometria, pl. Aaa (49). (US Naval Observatory,Retrieved on 2009-09-05)
  5. ^ 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)
  6. ^ http://www.centauri-dreams.org/?p=1468 See second Paragraph below inserted picture.
  7. ^ http://home.insightbb.com/~lasweb/lessons/magellanic.htm Home.insightbb.com Retrieved on 2007-05-31
  8. ^ 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.

External links


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Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.  Read more
Britannica Concise Encyclopedia. Britannica Concise Encyclopedia. © 2006 Encyclopædia Britannica, Inc. All rights reserved.  Read more
Sci-Tech Encyclopedia. McGraw-Hill Encyclopedia of Science and Technology. Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved.  Read more
Columbia Encyclopedia. The Columbia Electronic Encyclopedia, Sixth Edition Copyright © 2003, Columbia University Press. Licensed from Columbia University Press. All rights reserved. www.cc.columbia.edu/cu/cup/.  Read more
Wikipedia. This article is licensed under the Creative Commons Attribution/Share-Alike License. It uses material from the Wikipedia article "Magellanic Clouds".  Read more