Southern Skies: The Magellanic Clouds

The Magellanic Clouds consist of two irregular galaxies, the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC). Many early navigators used these two small galaxies to find their way across southern oceans. They were always noticeable in the southern sky and figured in early southern legends and myths.  They are close to the South Celestial Pole, so they never appear to set.

ESO’s Paranal Observatory shows the four Auxiliary Telescopes of the Very Large Telescope (VLT) Array, set against an incredibly starry backdrop on Cerro Paranal in Chile. The Small and Large Magellanic Clouds, visible only in the southern sky. These two irregular dwarf galaxies are in the Local Group and so are companion galaxies to our own galaxy, the Milky Way.

Al-Sufi, the Persian astronomer (903-986 C.E.) first described what would become the Large Magellanic Cloud in his Book of Fixed Stars in the year 964. He called it Al-Bakr, the White Ox of southern Arabia, after receiving reports from Arab navigators in the Malay Archipelago. We now know this group of stars as Nubecula Major (the greater Magellanic Cloud).

The first confirmed recorded observation was noted in 1504 by Amerigo Vespucci, in a letter about his third voyage. He mentioned “three Canopes, two bright and one obscure”; “bright” refers to the two Magellanic Clouds, and “obscure” referring to the Coalsack.

This image from the Wide Field Imager on the MPG/ESO 2.2-metre telescope shows part of the huge cloud of dust and gas known as the Coalsack Nebula. The dust in this nebula absorbs and scatters the light from background stars.

The explorations of Ferdinand Magellan would support these observations in 1519, on his voyage to the East Indies, with his crewmate, astronomer Antonio Pigafetta, describing:

“The Antarctic pole has no star of the fate of the Arctic pole, but we see many stars congregated together, which are like two nebulae, a little separated from each other, and a little in the middle.  Among these, there are two not very large nor very bright, which move little. And those two are the Antarctic pole.”

Subsequently, the name Magellanic Clouds would become the nomenclature for these nebulae, in honor of Ferdinand Magellan per Charles V, King of Spain.

Centuries later, Henrietta Swan Leavitt would study the Large and Small Magellanic Clouds from Harvard College Observatory in Southern Peru. In the early 1900s, she published her work on variable stars in the Small Magellanic Cloud, showing the relationship between the periods (cycles) of the stars’ variability and their luminosities. Her study was titled 1777 Variables In The Magellanic Clouds.

The period-luminosity curve allowed American astronomers Edwin Hubble, Harlow Shapley, and others to determine the distances of many Cepheid stars and consequently of the star clusters and galaxies in which they were observed. The most dramatic application was Hubble’s use in 1924 of a Cepheid variable to determine the distance to the great nebula in Andromeda, which was the first distance measurement for a galaxy outside the Milky Way. 

The Large Magellanic Cloud lies about 163 thousand light years from Earth. The Small Magellanic Cloud is about 200,000 light years away. Spectral Analysis shows a normal amount of helium, and the cold dust contains carbon and silicon. A low amount of metal points to the stars being young. The Large Magellanic Cloud contains a region called the Tarantula Nebula, where new stars appear to be formed often, possibly caused by the compression of interstellar gas and dust.

IMAGE: NASA, ESA, CSA, STScI, Webb ERO Production Team