The Andromeda Galaxy (M31) is the closest spiral galaxy to our own Milky Way. It is visible to the naked eye as a faint smudge on a dark moonless night; it is impressive in a small telescope; but it takes a long exposure photograph to reveal its full extent and structure.
Its tightly wound spiral arms harbor countless stars and cosmic dust. This image captures some of the intricate details of these spiral arms.
The Andromeda Galaxy (M31) and its Satellites (Mosaic of two 60 min total exposure Nov 19, 2023)
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M31 is approximately 2.5 million light-years away. It is closer and hence appears larger than any other galaxy (apart from the two Magellanic Clouds visible only from the southern hemisphere that are small satellites of our Milky Way). And it is on a collision course with us and will collide with our Milky Way in about four billion years.
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Like the Milky Way with its Magellanic Cloud satellites, M31 has two prominent satellite galaxies, M32 and M110. M32, a compact elliptical galaxy, appears as a distinctive celestial companion, nestled near the heart of Andromeda. M110, a larger elliptical galaxy, graces the frame with its glow, extending the canvas beyond the M31.
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NGC 206 is a star cloud contained within a spiral arm of the Andromeda Galaxy. It is the richest and most conspicuous such cloud and contains hundreds of new and extremely bright stars.
The Andromeda Galaxy was long assumed to be one of the nearest gaseous nebulae in own Milky Way, similar to many of the nebulae that I have shared pictures of recently. Later some astronomers came to believe it was instead another “island universe” similar to and far beyond the edge of the Milky Way. The debate was settled in 1925 by Edwin Hubble (for whom the space telescope was named) when he found and measured a number of Cepheid variable stars contained therein.
Andromeda is a fairly tightly-wound spiral galaxy that we see about 23 degrees away from being edge-on. Because of this, it is difficult to study its spiral structure. You can see very noticable dark dust clouds interspersed among the spiral arms, especially to the lower right (the portion of the disk nearest to us) and near the bottom left.
I shared an earlier picture of the Andromeda Galaxy that I took nearly four years ago. You can click here to revisit that post. That one was a 5 minute exposure – you can see how much more detail shows up in the recent 60 minute exposure!