What Is the Closest Galaxy to the Milky Way?

What is the closest galaxy to the Milky Way? The closest galaxy to the Milky Way was only recently discovered, and is named Canis Major. Just 42,000 light years from the Milky Way’s center, Canis Major is technically inside the Milky Way: already the Milky Way is swallowing stars from Canis Major. You can’t get much closer together than that.

Canis Major is the answer to what the closest galaxy to the Milky Way is.  Canis Major was discovered in 2003 by an international group of astronomers, who were observing the sky with the use of infrared technology. Infrared is capable of filtering through obstacles in the galaxy not previously possible, and so the astronomers can use it to pick out stars not visible with other types of observation equipment.

All About the Canis Major Galaxy

Compared to other galaxies, Canis Major - the closet galaxy to the Milky Way - is considered very tiny, with approximately one billion stars. The Milky Way, for example, holds 200 to 400 billion stars. It is believed that the Milky Way grew to its current size by doing exactly what it seems to be doing to Canis Major: encompassing it and making it part of itself. Thus, the discovery of Canis Major, which is already partially inside the Milky Way, was also a discovery of the fact that our own galaxy is bigger than we thought.

The Stars in Canis Major

The stars that make up Canis Major are comprised primarily of two specific types:

• M-Dwarf: The majority of the most common type of star within the Milky Way are called M-dwarf stars. M-dwarfs are very small and dim – too small to see from the earth – but they make up over half of the stars in the Milky Way.
• M-Giant: Although the Canis Major is the closest Galaxy to the Milky Way, we weren't always aware of it. So, what led us to it? It wasn’t the tiny, barely-visible M-dwarf stars that led the astronomers to find Canis Major. It was the larger, brighter M-giant stars. M-giant stars are easier to see than M-dwarf stars, but still aren’t very visible: in spite of their larger size, they’re still much cooler than other stars, and thus remain dim. The exception is when they are examined through infrared light.

Other Galaxies Close to the Milky Way

The answer to what is the closest galaxy to the Milky Way has actually changed. Before Canis Major was discovered, it was thought that a galaxy called the Sagittarius Dwarf Elliptical Galaxy was the closest to the Milky Way’s center. Also being encompassed by the larger galaxy, the Sagittarius was discovered in 1994 and measures approximately 75,000 light years from the center. 

Finally, there is one other way to look at this question. When asking about the closest galaxy to the Milky Way, the answer of Canis Major is correct. However, if you’re asking about the closest galaxy that is like our own, the answer changes. Both Canis Major and Sagittarius are different classifications of galaxies than the Milky Way. The nearest galaxy that is a spiral galaxy, like ours, is Andromeda.