The Magellanic Clouds are irregular galaxies that share a gaseous envelope and lie about 22° apart in the sky near the south celestial pole. The Magellanic Clouds are visible to the naked eye in the Southern Hemisphere, but they cannot be seen from most northern latitudes.
The Magellanic Clouds were formed at the same time as the Milky Way Galaxy, approximately 13 billion years ago. They are presently captured in orbits around the Milky Way Galaxy and have experienced several tidal encounters with each other and with the Galaxy. They contain numerous young stars and star clusters, as well as some much older stars.
The Magellanic Clouds serve as excellent laboratories for the study of very active stellar formation and evolution. For example, the Tarantula Nebula (also called 30 Doradus) is an immense ionized-hydrogen region that contains many young, hot stars. The total mass of 30 Doradus is about one million solar masses, and its diameter is 550 light-years, making it the largest region of ionized gas in the entire Local Group of galaxies. With the Hubble Space Telescope, it is possible for astronomers to study the kinds of stars, star clusters, and nebulae that previously could be observed in great detail only in the Milky Way Galaxy.
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