Astronomy

How the Magellanic Clouds were Discovered



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The Large and Small Magellanic Clouds are part of the Local Group cluster of galaxies, which includes the Milky Way, but they are not bound gravitationally to the Milky Way. They can be found in the southern constellation Mensa. Both Magellanic Clouds were known as separate sky objects since ancient times, but were not labeled as clusters of stars until Ferdinand Magellan's circumnavigation in the 16th century.

Ancient times

Although the Magellanic Clouds are in the south celestial hemisphere, as is the main part of the Milky Way, most ancient written records are from the northern hemisphere. However, Large and Small Magellanic Clouds can be seen, close to the horizon, from the most southerly points in the northern hemisphere.

The earliest known record of the Large Magellanic Cloud is from the Book of Fixed Stars, by the Persian astronomer Al Sufi. Although his work was a re-examination and update of Ptolemy's Almagest, he also added sky objects which could not have been seen by Ptolemy, who was based in Alexandria, Egypt.

The Large Magellanic Cloud is also invisible in Persia (modern-day Iran) and most of the Arabian peninsula. However, it can be seen from the Strait of Babd al Mandab, at 12 degrees 15 minutes north, near the southern tip of the Arabian peninsula between modern day Eritrea, Djibouti, and Yemen. Al Sufi included it among the fixed stars as Al Bakr, the White Ox.

The Magellanic Clouds also appear in the astronomy of the South Pacific islanders and the Australian aborigines. Darwin records the Polynesian name for the Magellanic Clouds as "fmthu," which means mist or vapor. They are distinguished with one being above ("ainanu") and the other below ("amino").

European voyages of discovery

The earliest European observation of the Magellanic Clouds may have been shortly after Columbus' own voyage of discovery. Toward the end of the 15th century, Italian explorers Peter Martyr d'Anghiera and Andrea Corsali are believed to have seen them.

Later, around 1503 or 1504, Amerigo Vespucci may have mentioned them in a letter which he wrote during his third voyage. Vespucci describes "three Canopes, two bright and one obscure." The 2 bright "Canopes" are believed to be the Magellanic Clouds, while the obscure one may be the Coalsack Nebula.

Their most famous mention during this time is by Antonio Pigafetta, who accompanied Magellan's expedition on his voyage around the world between 1519 and 1522. He was also the first person to describe them as dim clusters of stars.

Subsequent Portuguese and Dutch sailors referred to them as the Cape Clouds. They would not become known as the Magellanic Clouds for several centuries.

Astronomers

In his Uranometria (1603), Johann Bayer designated the Magellanic Clouds as nebecula major and nebecula minor. Nicolas Lacaille updated the Uranometria in his own Planisphere (1756), and marked the Magellanic Clouds as le Grand Nuage and le Petit Nuage. However, they are not included in Charles Messier's list, because it was exclusive to the northern hemisphere.

Between 1834 and 1838, John Herschel made detailed observations and measurements of the southern skies from the Royal Observatory at the Cape of Good Hope, using a 20-foot reflecting telescope. He described the Magellanic Clouds as cloudy masses of light with an oval shape and a bright center. By this point, the Magellanic Clouds were understood to be large, distant clusters of stars, which were later identified as galaxies.

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ARTICLE SOURCES AND CITATIONS
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