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If you’re lucky enough to live in the Earth’s southern hemisphere, you’re familiar with two fuzzy patches in the night sky. These are the Large and Small Magellanic Clouds, which may or may not be companion galaxies to our own Milky Way. The two Magellanic Clouds are separated by 21 degrees in the sky (that’s about 42 times the width of the full moon). But their true distance is about 75,000 light-years.
The Large Magellanic Cloud is located about 160,000 light-years away from the Milky Way in the constellation Dorado, making it the 3rd closest galaxy to us; only the Sagittarius Dwarf and Canis Major Dwarf galaxies are closer. It has the mass of about 10 billion times the mass of the Sun, making it about a tenth the mass of the Milky Way. It’s actually the 4th largest galaxy in our Local Group of galaxies, after the Milky Way, Andromeda and the Triangulum Galaxy. Astronomers have classified the LMC as an irregular type galaxy, but it does have a very prominent bar in its center, so it’s possible that it was a barred spiral before its gravitational interactions with the Milky Way.
The Small Magellanic Cloud is located in the constellation Tucana, about 200,000 light-years away. With the unaided eye, the Small Magellanic Cloud looks like a small hazy patch detached from the Milky Way. In fact, it’s one of the most distant objects you can see with the unaided eye.
Astronomers used to think that the Magellanic Clouds were companion galaxies to the Milky Way, but recent velocity measurements have calculated that they’re not gravitationally bound to the Milky Way. Instead, they’re just passing nearby us before they travel away again.
These galaxies are different from the Milky Way in a few ways. For starters, they’re gas rich, which means they can still have large amounts of new star formation. They’re also metal poor, which means that they haven’t had many generations of star formation already.
The Magellanic Clouds were named after the explorer Ferdinand Magellan, who first observed the clouds during the circumnavigation of the Earth in 1519–1522,
We have written many articles about the Magellanic Clouds for Universe Today. Here’s an article about how their velocity was calculated, and astronomers discovered that the Magellanic Clouds are just passing by.
If you’d like more info on galaxies, check out Hubblesite’s News Releases on Galaxies, and here’s NASA’s Science Page on Galaxies.
We have also recorded an episode of Astronomy Cast about galaxies – Episode 97: Galaxies.
References:
ESO
Hyperphysics
About Fraser Cain
Fraser Cain is the publisher of Universe Today. He's also the co-host of Astronomy Cast with Dr. Pamela Gay.
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