written by: Nick Oza•edited by: RC Davison•updated: 4/22/2011
The Milky Way Galaxy has two satellite galaxies known as the Magellanic clouds. We will explore the Large Magellanic Cloud and the Small Magellanic Cloud and describe what type of galaxies they are, a brief history of them, notable events in the clouds and where to find them in the night sky.
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History of Human Observations
The Magellanic Clouds were observed by the ancients for several millennia. The Persian astronomer Al-Sufi was the first to mention the Large Magellanic Cloud (LMC) in 964 AD in one of his books. Circumnavigator, Ferdinand Magellan brought the LMC to the attention of Europe during one of his voyages. The Small Magellanic Cloud (SMC) was first noticed by European sailors during voyages when they were used for navigational purposes.
Collectively, the clouds were referred to as the Cape Clouds by Dutch and Portuguese sailors. They were known by this name for several centuries and were later named in honor of Magellan. It was not until the 1900s that the distance to the SMC was first calculated by astronomers. The Large and Small Magellanic Clouds are neighboring dwarf galaxies.
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The Large Magellanic Cloud (LMC)
The LMCis an irregular dwarf galaxy located 160,000 light years from Earth. The galaxy is part of the Local Group of which includes the Milky Way. Within the Local Group it is the fourth largest galaxy, the first three being the Andromeda galaxy, the Milky Way galaxy and the Triangulum galaxy. The LMC is the third nearest galaxy to our own, the other two being Sagittarius Dwarf and Canis Major Dwarf.
The LMC is composed of some 10 billion stars and is 14,000 light years across. The galaxy contains plenty of gas and dust and is undergoing star formation at a rapid rate. Several globular clusters, planetary nebulae and open clusters have been discovered within the LMC. In addition, the galaxy contains a large number of giant and supergiant stars.
Since the galaxy has plenty of star forming regions, the most notable being the Tarantula nebula, it is considered as an excellent source to study the birth and evolution of stars. The LMC may be a satellite galaxy of the Milky Way, that is, it may be gravitationally bound to the Milky Way Galaxy. This is currently being researched.
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The Small Magellanic Cloud (SMC)
The SMC is also an irregular dwarf galaxy and is located some 200,000 light years from Earth. It is smaller than its neighbor, the LMC and is approximately 7,000 light years across. At some point in the past, the SMC may have had a barred spiral shape, but it was distorted due to the gravitational effects of a passing galaxy or probably the Milky Way itself. The galaxy contains several open clusters, planetary nebulae, nebulae, supernova remnants and one globular cluster. The SMC is also part of the Local Group and like the LMC it may be a satellite galaxy of the Milky Way.
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Notable Event in the LMC
In 1987, a supernovawas observed by astronomers in the Tarantula Nebula, located in the LMC. The supernova occurred at a distance of 51.4 kiloparsecs from Earth, making it visible to the naked eye. The supernova was discovered by astronomers working at the Las Campanas Observatory in Chile.
It was officially named SN 1987A. The supernova event tool place in the Tarantula Nebula, which is the most active star forming region in the Local Group. Since SN1987A is located 51.4 kiloparsecs or 168,000 light-years from Earth, the supernova happened somewhere around 168,000 light-years ago and the light from the dying star reached Earth on February 23, 1987.
In the image to the right, the supernova remnant is in the center of the picture, surrounded by a glowing ring of debris, with two fainter rings above and below it.
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Where to See Them?
The Magellanic Clouds are only visible from the Southern Hemisphere. An observer would have to travel south and for those observers located 20 degrees South latitude, the LMC is circumpolar. You can find the LMC about 22 degrees from the South Celestial Pole, located between the constellations of Dorado and Mensa. The stars in this region are faint and the LMC appears as a faint galaxy, but with the aid of a telescope it can be viewed in more detail.
The SMC is located some 20 degrees from the South Celestial Pole in the south-eastern region of the constellation Tucana. An easier way to find the SMC is by spotting the bright star Achemar in the constellation Eridanus the River and looking about 15 degrees below Achemar. The SMC appears fainter than the LMC and is better visible on darker nights.