Andromeda Galaxy Facts

The Andromeda Galaxy is also called M31 or Messier 31, and is a spiral galaxy like our Milky Way galaxy.

Andromeda Galaxy Profile

Also known as:Messier 31, M31, or NGC 224
Type:Spiral Galaxy
Diameter:220,000 light years
Distance:2.54 Million light years
Mass:1,230 billion M☉
Number of Stars:1 trillion

It is located around 2.5 million light-years from Earth in the Andromeda constellation.

The Andromeda Galaxy is the closest neighbor to our Solar System, but not the closest galaxy to the Milky Way. The Andromeda Galaxy, along with the Milky Way and Triangulum Galaxies are part of a “Local Group” that contains more than 54 galaxies.

The name for the Andromeda Galaxy is taken from the constellation of Andromeda where it is located.

Named after a mythological Greek princess, it’s considered to be the most massive of all of the galaxies in the local group.

The Milky Way Galaxy was found to be around 80% of the mass of the Andromeda Galaxy in a 2006 research study.

How big is the Andromeda Galaxy

To give you an idea of the size comparison, the Milky Way Galaxy has around 200-400 billion stars, whereas the Andromeda Galaxy has around 1 trillion stars.

Believed to have formed around 5-9 billion years ago when two smaller galaxies merged during a collision, the Andromeda Galaxy is bright enough to be seen by the naked eye during a moonless night.

Scientists have estimated that in 3.75 billion years the Milky Way and Andromeda Galaxies will collide.

The resulting merger will create a giant elliptical galaxy. The speed that Andromeda is approached the Milky Way is about 110 km/second.

The Andromeda Galaxy center is thought to be the home of at least 26 known candidates for being black holes. The Chandra X-ray Observatory have selected even more that are potentials.

Both the Milky Way and Andromeda Galaxies have supermassive black holes at their center and there are two additional possibilities that are orbiting as a binary, having a mass of 140 million times that of our Sun.

Facts about Andromeda

  • Andromeda has a lot of satellite galaxies, including 14 dwarf galaxies. It acts as a kind of “bully” in the neighborhood, ripping off stars and robbing them of a large part of the stellar disk.
  • Andromeda Galaxy is visible from August to February in the Northern Hemisphere, and from October to December in the northern horizon of the Southern Hemisphere.
  • If you want to find the Andromeda Galaxy you simply look for the constellations of Cassiopeia and Pegasus. If you draw a line from one corner to the other it will give you an excellent idea of where to look for the Andromeda Galaxy.
  • When you have the perfect observation time to see the Andromeda Galaxy it appears to be six times wider than our full moon.
  • Until the 1920’s, the Andromeda Galaxy was thought to be a Nebula, which consists of only clouds of gas.
  • At the heart of the Andromeda Galaxy is a supermassive black hole that is located at its center bulge. Surrounding the black hole is a disk that contains an elliptical ring of older blue and red stars.
  • It is thought that the blue stars in the Andromeda Galaxy are the oldest, waiting to become red giants.
  • One of the big differences between the Milky Way and Andromeda Galaxies is that Andromeda has a double-nucleus which is believed to have been caused by the collision of two smaller galaxies.
  • The astronomer Heber Doust Curtis (1872-1942) studied the Andromeda Nebula as well as exploding stars known as novae and came to the first Island Universe theory that included more than just our Milky Way Galaxy.
  • In 1925, Edwin Hubble took on the great debate regarding the existence of galaxies when he calculated the distance of the Andromeda Nebula proving that it was outside of the Milky Way Galaxy.


  • What other name is used when referring to the Andromeda Galaxy?
    M31 or Messier 31
  • What major characteristic does the Andromeda Galaxy have that is completely different from the Milky Way Galaxy?
    it has a double-nucleus
  • The study of the Andromeda Galaxy helped to prove what theory?
    Island Universe theory
  • What bad behavior does the Andromeda Galaxy demonstrate to its 14 satellite dwarf galaxies?
    it acts like a bully
  • If you look at the Andromeda Galaxy on a perfect night how much bigger does it appear than our Moon?
    six times bigger
  • How many galaxies are in the Local Group that contain both the Milky Way and Andromeda?