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The Sagittarius Dwarf Elliptical Galaxy is the third closest neighboring galaxy to the Milky Way Galaxy, which is where our solar system is located. At only 50,000 light years distant from the Milky Way's core, the Sagittarius Galaxy is engaging in a polar orbit around the Milky Way, which is slowly devouring it. Even now, the Sagittarius Galaxy is leaking out a stellar stream, a filament which stretches around the Milky Way's core like a gossamer loop. The Sagittarius Galaxy is named after the constellation where it can be found, Sagittarius.
Discovered in 1994, the Sagittarius Dwarf Elliptical Galaxy is only about 10,000 light years in diameter, in comparison to the Milky Way's diameter of 100,000 light years. The Milky Way Galaxy is estimated to be about 10,000 times more massive than the Sagittarius Galaxy. Up until 2003, it was thought to be the closest galaxy to the Milky Way, although this spot has recently been taken by the Canis Major Dwarf Galaxy, which is also being devoured by the Milky Way. Both galaxies, along with about eight others, are considered satellites of the Milky Way Galaxy.
The Sagittarius Galaxy has about a billion stars, compared to the Milky Way's 200-400 billion stars. Although it takes up a portion of the sky similar to a full moon, the Sagittarius galaxy is very faint because most of it is obscured by the galactic disc. Its central star cluster, M54, was discovered all the way back in 1778 by Charles Messier, making it the first extragalactic star cluster discovered, although it took the astronomy community more than two centuries to realize this.
The Sagittarius Dwarf Elliptical Galaxy is one of the few galaxies to be on a direct collision course with the Milky Way. It will pass through the galactic disc in roughly a hundred million years. But since galaxies themselves are very diffuse, this will barely increase the incidence of stellar collisions.