Magellanic Clouds(redirected from Clouds of Magellan)
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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. The LMC is some 160,000 light-years from the earth; the SMC, some 200,000 light-years. They are part of the Local GroupLocal Group,
in astronomy, loose cluster of at least 40 nearby galaxies, including our own Milky Way galaxy, the Andromeda Galaxy, and the Magellanic Clouds. The Local Group is spread over an ellipsoidal region of space with a major axis of approximately 3 million light-years.
..... Click the link for more information. of galaxies, which includes our own galaxy (the Milky WayMilky Way,
the galaxy of which the sun and solar system are a part, seen as a broad band of light arching across the night sky from horizon to horizon; if not blocked by the horizon, it would be seen as a circle around the entire sky.
..... Click the link for more information. ) and the Andromeda GalaxyAndromeda Galaxy,
cataloged as M31 and NGC 224, the closest large galaxy to the Milky Way and the only one visible to the naked eye in the Northern Hemisphere. It is also known as the Great Nebula in Andromeda. It is 2.
..... Click the link for more information. , and are the nearest extragalactic objects.
The Magellanic Clouds, named for the Portuguese navigator MagellanMagellan, Ferdinand
, Port. Fernão de Magalhães, Span. Fernando de Magallanes, c.1480–1521, Portuguese navigator who sailed for Portugal and Spain. Born of a noble family, he was reared as a page in the royal household.
..... Click the link for more information. , were first studied in detail by Sir John HerschelHerschel
, family of distinguished English astronomers. Sir William Herschel
Sir William Herschel, 1738–1822, born Friedrich Wilhelm Herschel, was a great pioneer in astronomy.
..... Click the link for more information. in the 19th cent. While studying Cepheid variableCepheid variables
, class of variable stars that brighten and dim in an extremely regular fashion. The periods of the fluctuations (the time to complete one cycle from bright to dim and back to bright) last several days, although they range from 1 to 50 days.
..... Click the link for more information. 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.
Magellanic Clouds(maj-ĕ-lan -ik, mag-) Two comparatively small irregular galaxies that are close neighbors of our own Galaxy. Both are naked-eye objects but, being close to the south celestial pole, they are visible only from the southern hemisphere. They were first recorded in 1519 by Ferdinand Magellan. The Large Magellanic Cloud (LMC) has a diameter of about 10 000 parsecs; it lies in the constellation Dorado at a distance of about 50 000 parsecs. The Small Magellanic Cloud (SMC) has a diameter of about 6000 parsecs; it lies in the constellation Toucan and is about 60 000 parsecs away.
Both the LMC and SMC are rich in population I objects and contain a much greater proportion of gas than our own Galaxy. They are enveloped in a common cloud of cool neutral hydrogen, which extends into a narrow streamer. This Magellanic Stream stretches over 110° of the sky, extending toward the Galaxy. The Stream contains almost 109 solar masses of gas, probably ripped out of one or both Magellanic Clouds when they passed near the Galaxy about 200 million years ago and now strewn along the orbit of the Clouds. If the Galaxy has a massive dark halo, the Magellanic Clouds are gravitationally bound as satellites of the Galaxy and they have probably made several close approaches; otherwise, they have been involved in just one encounter, and the Magellanic Stream marks a hyperbolic orbit.
(Large and Small Magellanic Clouds), two stellar systems (galaxies) of irregular shape, the nearest stellar systems to our stellar system, the Milky Way Galaxy, which includes the sun. The Magellanic Clouds are visible to the unaided eye from the southern sky in the form of nebulous patches; the Clouds are not visible in the middle latitudes of the northern hemisphere. They are called the Magellanic Clouds because their discovery is attributed to one of the members of the voyage around the world led by F. Magellan (1519-22).
The Large Magellanic Cloud is located in the constellation Dorado, and the Small Magellanic Cloud in the constellation Tucana. The distance to both Magellanic Clouds from the sun has been determined from observations of the many cepheid variable stars. Data on the Magellanic Clouds are given in Table 1.
|Table 1. Data on Magellanic Clouds|
|Large Magellanic Cloud||Small Magellanic CloudCloud|
|Distance from sun (kpc)............||55||55|
|Apparent diameter......... . .||˜7°||˜4°|
|Absolute Photographic stellar magnitude ............||-18.1||-16.2|
The Magellanic Clouds contain an extremely large number of star clusters, gaseous nebulae, different types of variable stars, and other objects. The star S Doradus, whose photographic luminosity is 120,000 times greater than that of the sun, is found in one of the star clusters of the Large Magellanic Cloud. The Large Magellanic Cloud also contains the giant gaseous nebula 30 Doradus (the Looped Nebula). If this nebula were located at the same distance from Earth as the Orion Nebula (300 parsecs), then objects on the earth illuminated with its light would have observable shadows.