The Magellanic Clouds (or Nubeculae Magellani) are two irregular dwarf galaxies visible from the southern hemisphere; they are members of the Local Group and are orbiting the 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 (LMC), approximately 160,000 light-years away
- Small Magellanic Cloud (SMC), approximately 200,000 light years away
Probably the oldest continuous cultural references to the clouds come from the Khoi San peoples of Southern Africa. The ancestors of these people appear to have been quite separate from all other living humans for 100 to 200 thousand years. Examples of surviving references can be found at https://assa.saao.ac.za/astronomy-in-south-africa/ethnoastronomy/
Another long history of cultural association may have reemerged with the migration of humans south from the Middle East reaching Australia approximately 50 to 60 thousand years ago. Those people were the ancestors of the Aborigines, whose various cultures have a variety of stories about these galaxies, for example, those at http://aboriginalastronomy.blogspot.com/2011/08/adnyamathanha-night-skies-part-ii.html
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, under Argo Navis, he quoted that "unnamed others have claimed that beneath Canopus there are two stars known as the 'feet of Canopus' , and beneath those there are bright white stars that are unseen in Iraq nor Najd, and that the inhabitants of Tihama call them al-Baqar [cows], and Ptolemy did not mention any of this so we [Al-Sufi] does not know if this is true or false."
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.
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 ("the Large Cloud" and "the Small Cloud").
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 (since 2003, the Canis Major Dwarf Galaxy was discovered to be closer still, and is now considered the actual nearest neighbor). 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 (14,000 ly and 7,000 ly respectively). For comparison, the Milky Way is about 100,000 ly across.
The total mass of these two galaxies is uncertain. Only a fraction of their gas seems to have coalesced into stars and they probably both have large dark matter halos. One recent estimate of the total mass of the LMC is about 1/10 that of the Milky Way. That would make the LMC rather a large galaxy in the present era of the observable universe. Since the size of relatively nearby galaxies are highly skewed, the average mass can be a misleading statistic. In terms of rank, the LMC appears to be the fourth most massive member of over 50 galaxies in the local group. Suggesting that the Magellanic cloud system is historically not a part of the Milky Way is evidence that the SMC has been in orbit about the LMC for a very long time. The Magellanic system seems most similar to the distinct NGC 3109 system, which is on the edge of the Local Group.
Astronomers have long assumed 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. The LMC maintains a very clear spiral structure in radio-telescope images of neutral hydrogen. 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.
Measurements with the Hubble Space Telescope, announced in 2006, suggest the Magellanic Clouds may be moving too fast to be long term companions of the Milky Way. If it is in orbit, that orbit takes at least 4 billion years. It is possibly on a first approach and we are witnessing the start of a galactic merger that may overlap with the Milky Way's expected merger with The Andromeda Galaxy (and perhaps Triangulum) in the future.
Mini Magellanic Cloud (MMC)
Astrophysicists D. S. Mathewson, V. L. Ford and N. Visvanathan proposed that the SMC may in fact be split in two, with a smaller section of this galaxy behind the main part of the SMC (as seen from Earth's perspective), and separated by about 30,000 light years. 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.
- Astronomical surveys of the Magellanic Clouds
- Irregular galaxy
- Magellanic Stream
- Magellanic Bridge
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