The two Magellanic Clouds are a duo of irregular dwarf galaxies visible from
the southern hemisphere, which are members of our Local Group and may be
orbiting our Milky Way galaxy. Because they both show signs of a bar structure,
they are often reclassified as Magellanic spiral galaxies. The two
galaxies are: Large Magellanic Cloud
Small Magellanic Cloud History
The Magellanic Clouds were known to the Polynesians and served as important
navigation markers. Collectively they were known to Māori of New Zealand as
Nga Patari-Kaihau or as Te Reporepo and were also used as predictors of winds.
The Magellanic Clouds have been known since the first millennium in Western
Asia. The first preserved mention of the Large Magellanic Cloud is by the Persian
astronomer Al Sufi. In 964, in his Book of Fixed Stars, he called it al-Bakr "of
the southern Arabs"; he noted that the Cloud is not visible from northern
Arabia and Baghdad, but can be seen at the strait of Bab el Mandeb, which is
the southernmost point of Arabia. In Europe, the Clouds were first
observed by Italian explorers Peter Martyr d'Anghiera and Andrea Corsali at
the end of the 15th century. Subsequently, they were reported by
Antonio Pigafetta, who accompanied the expedition of Ferdinand Magellan on its
circumnavigation of the world in 1519–1522. However, naming the clouds
after Magellan did not become widespread until much later. In Bayer's Uranometria
they are designated as nubecula major and nubecula minor. In the 1756 star map
of the French astronomer Lacaille, they are designated as le Grand Nuage and le
Petit Nuage. In Sri Lanka, from ancient times, these
clouds have been referred to as the Maha Mera Paruwathaya meaning "the great
mountain", as they look like the peaks of a distant mountain range.
Characteristics The Large Magellanic Cloud and its
neighbour 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. The LMC lies about 160,000 light years away, while the SMC
is around 200,000. The LMC is about twice the diameter of the SMC. For
comparison, the Milky Way is about 100,000 ly across.
Astronomers have long believed that the Magellanic Clouds have orbited the Milky
Way at approximately their current distances, but evidence suggests that it
is rare for them to come as close to the Milky Way as they are now. 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. Their gravity
has affected the Milky Way as well, distorting the outer parts of the
galactic disk. 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. 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. 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.
The Large Magellanic Cloud was host galaxy to a supernova, the brightest
observed in over four centuries. Announced in 2006, measurements with the
Hubble Space Telescope suggest the Large and Small Magellanic Clouds may be
moving too fast to be long term companions of the Milky Way.
Mini Magellanic Cloud It has been proposed by astrophysicists
D. S. Mathewson, V. L. Ford and N. Visvanathan that the SMC may in fact be
split in two, with a smaller section of this galaxy behind the main part of the
SMC, and separated by about 30,000 ly. They suggest the reason for this is due
to a past interaction with the LMC splitting the SMC, and that the two
sections are still moving apart. They have dubbed this smaller remnant the
Mini Magellanic Cloud. In fiction
See also Astronomical Surveys of the Magellanic
Clouds Irregular galaxy
Magellanic Stream Magellanic Bridge
References Sources
Eric Chaisson and Steve McMillan, Astronomy Today, p. 550.
Michael Zeilik, Conceptual Astronomy, pp. 357–8.
External links Magellanic Clouds Working Group