At a distance of about 2.5 million light years, the Andromeda galaxy (also known as NGC 224 and M31) is the nearest galaxy to the Earth apart from smaller companion galaxies such as the Magellanic Clouds.
Like the Milky Way, Andromeda is a spiral galaxy. It can be spotted with the naked eye and so has been known to humans for a very long time.
In the 1920s astronomer Edwin Hubble confirmed that Andromeda is another galaxy and not just a gas cloud in the Milky Way as was previously thought.
Image: A mosaic view of the Andromeda galaxy created from 10 Galaxy Evolution Explorer images (credit: NASA/JPL-Caltech)
A nearby galaxy is similar to our own.
Edwin Hubble discovers galaxies outside the Milky Way.
Edwin Hubble discovers galaxies outside the Milky Way and measures how far away they are.
Patrick Moore and his guests discuss galaxies.
Sir Patrick Moore and his guests explain what galaxies are and discuss some of their interesting features.
The great astronomer worked at Mount Wilson Observatory.
This clip was filmed at a time when the Hubble Space Telescope had been discovered to have a flawed mirror, hence the reference to "failure". The Hubble Space Telescope went on to become one of the most successful NASA missions. This clip looks at some of the American astronomer Edwin Hubble's most important contributions to astronomy and the equipment he used at the Mount Wilson Observatory. The age of the Universe is now thought to be 13.7 billion years.
Patrick Moore discusses the Magellanic Clouds.
Sir Patrick Moore discusses the Magellanic Clouds, supernovae, and other sights.
Prof Brian Cox takes a closer look at the spiral galaxy Andromeda.
Prof Brian Cox takes a photograph of the spiral galaxy Andromeda, seeing the light it emitted 2.5 million years ago.
The Andromeda Galaxy (//) is a spiral galaxy approximately 780 kiloparsecs (2.5 million light-years; 2.4×1019 km) from Earth. Also known as Messier 31, M31, or NGC 224, it is often referred to as the Great Andromeda Nebula in older texts. The Andromeda Galaxy is the nearest major galaxy to the Milky Way, but not the nearest galaxy overall. It gets its name from the area of the sky in which it appears, the constellation of Andromeda, which was named after the mythological princess Andromeda. The Andromeda Galaxy is the largest galaxy of the Local Group, which also contains the Milky Way, the Triangulum Galaxy, and about 44 other smaller galaxies.
The Andromeda Galaxy is the most massive galaxy in the Local Group as well. Despite earlier findings that suggested that the Milky Way contains more dark matter and could be the most massive in the grouping, the 2006 observations by the Spitzer Space Telescope revealed that M31 contains one trillion (1012) stars: at least twice the number of stars in the Milky Way, which is estimated to be 200–400 billion.
The Andromeda Galaxy is estimated to be 1.5×1012solar masses, while the mass of the Milky Way is estimated to be 8.5×1011 solar masses. In comparison a 2009 study estimated that the Milky Way and M31 are about equal in mass, while a 2006 study put the mass of the Milky Way at ~80% of the mass of the Andromeda Galaxy. The two galaxies are expected to collide in 3.75 billion years, eventually merging to form a giant elliptical galaxy or perhaps a large disk galaxy.
At 3.4, the apparent magnitude of the Andromeda Galaxy is one of the brightest of any Messier objects, making it visible to the naked eye on moonless nights even when viewed from areas with moderate light pollution. Although it appears more than six times as wide as the full Moon when photographed through a larger telescope, only the brighter central region is visible to the naked eye or when viewed using binoculars or a small telescope.