Andromeda galaxy
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The Andromeda Galaxy is a spiral galaxy similar to the Milky Way, and situated within the same galactic cluster called the Local Group.
It is situated about 2.51 ± 0.13 million light years from the Milky Way, and it is on a collision course with us to hit sometime in about 3 to 5 billion years; it is likely to move, 'through' our galaxy, although, since both are mostly empty space, it is unlikely that planets or stars will collide.[1][2]
The number 2.51 million light years has been reached through three separate methods for determining the distance to an astronomical object.
- Cepheid variables
- Eclipsing binary star[3]
- Measurement of brightness of individual stars and comparing to the distance to the Magellanic Clouds