The Andromeda Galaxy is the closest big galaxy to Milky Way and is located over 2 million lightyears away.
The Andromeda Galaxy is notable for its bright blue tinge, which is caused by pockets of hot young stars burning bright blue.
It can be seen in the night sky in the northern hemisphere throughout much of the year, but is best seen in autumn.
What's more, it can be seen with the naked eye under good conditions. For more on this, read our guide on how to see the Andromeda Galaxy.
The Andromeda Galaxy and the Milky Way are gravitationally interacting, and astronomers have calculated that both galaxies will collide in about 4.5 billion years time. This event is known as the Andromeda-Milky Way collision.
Andromeda Galaxy and the Great Debate
Observations of the Andromeda Galaxy have led to some of the most important discoveries in the Universe: particularly its part in the Great Debate, in which astronomers Harlow Shapley and Heber Curtis debated about whether other galaxies existed beyond our own.
The matter was settled largely because of the work of Edwin Hubble, after whom the Hubble Space Telescope was named.
Hubble was able to photograph individual stars in the 'Andromeda Nebula' (as it was then known) and in 1923, his observations of Cepheid variable stars led him to conclude that the Andromeda Galaxy must be located beyond our own Galaxy.
Below is a selection of images of the Andromeda Galaxy captured by astrophotographers and BBC Sky at Night Magazine readers.