The Magellanic Clouds

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The Magellanic Clouds

Both the LMC and SMC were named after the Portuguese explorer Ferdinand Magellan (1480-1521) who mistakenly believed they were clouds. While the LMC is only approximately 163,000 light years from us, the SMC is not much farther at about 199,000 light-years. In order to envision this, our entire Milky Way Galaxy is 100,000 light-years across, and it is approximately 3,000,000 light-years away from the approaching Andromeda Galaxy (M31).

Over twenty small satellite galaxies circle our own, but only the duo of Magellanic Clouds are bright enough to be viewed from Earth with the unaided human eye. Both the LMC and SMC are brimming with gas, in dramatic contrast to our Milky Way’s other orbiting galactic satellites, and gas is the stuff that stars are made of. For this reason, both Magellanic Clouds are sufficiently rich in gas to create brilliant new fiery baby stars.

The people of several ancient cultures knew of the existence of the Magellanic Clouds. The most ancient continuous extant references to the pair of “clouds” were likely conducted by ancient sky-watchers from the Khoisan culture located in Southern Africa. The ancestors of these people are thought to have lived in isolation from other living human cultures for thousands of years.

Another substantially long history of cultural association may have re-emerged with the migration of ancient humans south from their region of origin in the Middle East. These migrating people are thought to have reached Australia approximately 50 to 60 thousand years ago, and they were the ancient forebears of modern Aborigines, whose several cultures have created a variety of interesting and colorful myths, legends, and folktales centered around this mesmerizing duo of starlit satellite galaxies.

The ancient people of Polynesia were also aware of the existence of this bewitching pair of “clouds”, and they used them as navigation markers. Taking both “clouds” together, the duo were also known to the Maori of New Zealand as Nga Patori-Kaihau or as Te Reporepo. The ancient Maori used the pair of “clouds” as predictors of winds.

The Magellanic Clouds

Even though both “clouds” have been readily visible to the prying eyes of southern nighttime sky-watchers well back into prehistoric times, the first known written reference to the LMC was made by the Persian astronomer ‘Abd al-Rahman al-Sufi Shirazi (303 AD-986 AD)–later known in Europe as “Azophi”–in his Book of Fixed Stars (~964 A.D.).

The second recorded observation of the Magellanic Clouds was made in 1503-4 by the Italian explorer Amerigo Vespucci ((1454-1512) in his letter describing his third voyage. In this letter, Vespucci mentions “three Canope [sic], two bright and one obscure”; “bright” here refers to the LMC and SMC, while “obscure” refers to the Coalsack Nebula, a cloud composed of gas and dust, that is the most prominent dark nebula in the skies.

Measurements conducted with the Hubble Space Telescope (HST), that were announced back in 2006, indicate that both Magellanic Clouds are actually traveling too fast to be orbiting our Milky Way. For some time, many astronomers proposed that both Magellanic Clouds had been in orbit around our Milky Way at approximately their current distances for eons. However, more recent observations indicate that it is rare for the duo to be located as close to our Galaxy as they are now. Both theory and observation indicate that the “clouds” have both been greatly distorted by tidal interactions with our own considerably larger Galaxy as they travel ever closer and closer to it.

The distance to the LMC has been determined by astronomers using several different methods that depend on “standard candles”, with Cepheid variables being one of the most favored “candles”. “Standard candles” are astrophysical objects such as supernovae or variable stars, which have known luminosity because of some characteristic quality possessed by its entire class of objects. Cepheids are intrinsic variable stars that pulsate in a predictable way, and have long been known to display a relationship between their absolute luminosity and the period over which their brightness changes. However, Cepheids are often considered to be inadequate because they suffer from a “metallicity effect”. This means that Cepheids of differing metallcities show different period-luminosity relations. Alas, the Cepheids that flicker brightly in our Milky Way, that are usually used to calibrate the period-luminosity relation, are more rich in metals than those found dwelling within the LMC.

In astronomy, the term metal differs from the same term as it is used by chemists. The Big Bang birth of the Universe, thought to have occurred about 14 billion years ago, produced only the lightest of atomic elements: hydrogen, helium, and trace amounts of lithium. All of the atomic elements heavier than helium are called metals by astronomers. Metals, in the terminology used by astronomers, originate in the hot nuclear-fusing cores of the Universe’s myriad stars–or, alternatively, in the case of the heaviest atomic elements (such as gold and uranium), in the supernovae explosions that mark the end of a massive star’s life on the hydrogen-burning main-sequence of the Hertzsprung-Russell Diagram of Stellar Evolution. mkvmoviesking

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