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Nearest Galaxy [Q&A]


We had a Science Day at Cambridge recently and the SAO ran an Open House where people could come and ask questions of astronomers. One question that came up repeatedly was, what is the galaxy that is nearest to us?

It depends on how you define the term. If you are looking for a galaxy that is “like” the Milky Way, that is, a large spiral galaxy, then the answer is the Andromeda Galaxy, M31, which is about 780 kiloparsecs (two and a half million light years) away.

If you are simply looking for large conglomerations of stars, even if irregularly shaped, then the Small and Large Magellanic Clouds, at a distance of 60 and 50 kiloparsecs respectively (200 thousand and 160 thousand light years), are nearer. They are fairly small compared to the Milky Way, with the LMC only about 14000 light years wide.

If you are not particular about there being a coherent confined structure to define a galaxy, then there is the Sagittarius Dwarf Elliptical, which has pretty much been torn to shreds by tidal forces of our Galaxy and now forms a big loop like stream that cuts through the plane of the Milky Way. In fact, one arm of the stream is actually in the solar neighborhood. The core of Sag DEG is about 90 thousand light years almost perpendicularly away from the core of the Milky Way.

That’s not the end of the story. There’s another tidally disrupted galaxy called the Canis Major Dwarf Galaxy, whose core is only 40 thousand light years from the core of the Milky Way. Its tidal streams don’t come near the solar neighborhood however, as the Sag DEG’s do.