The Andromeda Galaxy: A Galactic Stepping Stone

Posted by Kelly on November 16th, 2012

M31, The Andromeda Galaxy

A view of the Milky Way’s future partner, the Andromeda Galaxy.

The Andromeda Galaxy is one of the best deep-sky targets for autumn and the easiest galaxy to spy. Located in the constellation Andromeda, it is often found using the right half of the W-shape in Cassiopeia to point the way down to it. At magnitude 3.4, it can even be seen without any optical aid, but it’s best to look with a telescope or binoculars first to nail down the location and then try looking with your eyes alone.

M31, as the Andromeda Galaxy is also known, is unmistakable once you have it in the eyepiece. It’s not a bright light that jumps out at you but the large oval of milky gray with its brighter core that makes it stand out from the thousands of stars and background darkness of space. For whatever reason, when I look at Andromeda it always reminds me of the seed of a milkweed, with its solid-looking oval core that is surrounded by a tenuous fuzz.

Andromeda is the nearest spiral galaxy to the Milky Way and the largest member of our Local Group of galaxies. At 2.3 million light-years distant, the light from Andromeda that reaches our eyes left the galaxy 2.3 million years ago, giving us a glimpse into the galaxy’s past. At 150,000 light-years wide, it surpasses the Milky Way’s 100,000 light-year girth and it has twice as many globular clusters as we do. Its brightest globular cluster, G1 or Mayall II, is magnitude 13.72 and can be spotted with a 10-inch telescope. It also has two brighter companion galaxies, the 8th magnitude ellipticals M32 and M110, which you may be able to spot with binoculars.

The Andromeda Galaxy is moving toward us at 266 kilometers a second, which is the fastest velocity known for a galaxy. One day the Milky Way and Andromeda will collide and merge into one enormous galaxy. The Local Group of galaxies, of which the Milky Way and Andromeda are a part, are a group of about 50 gravitationally bound galaxies that are blue-shifted because we are being pulled together. But the Local Group is part of a larger group called the Virgo Supercluster. The Virgo Supercluster is so massive that the different galaxy groups’ outward movement from one another will eventually be overcome as the galaxies stop and then begin to barrel back together. This will happen about 100 billion years from now and would be quite an amazing show if anyone were around to see it. Eventually (about 2 trillion years from now) space will expand beyond the limits of what we can see and any sentient beings still in the Milky Way will not be able to view the universe beyond the Virgo Supercluster.

Put in perspective, looking 2.3 million light-years out to Andromeda is merely a stepping stone to the greater universe at large, and we are lucky to live in a time when we are still able to view and ponder the cosmos’s vast expanses.

3 people have commented


Thrilling. I love the article but I want to know, between Andromeda and the milky way, which is older?

Kelly said,

Judging from the ages of the stars, the Milky Way Galaxy is believed to be about 14 billion years old. Andromeda is a bit younger, at about 10 billion years old it was created through the collision of smaller galaxies.

horseman said,

Andromeda (M31) is younger, but it’s velocity is greater than our M.W. due to its
position relative to the structure of the cosmos. However, it is NOT where it appears to be, and I am talking not even remotely!! The merging of M31 with M.W. has ALREADY begun! Its stars will (read HAVE) collide with stars in the M.W. at merging velocities in the neighborhood of 1.75c. So you can take that to the bank, and along the way, throw Albert’s “theory” of absolutes in the toilet.

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