Andromeda, the Constellation and the Galaxy

A few weeks ago, I wrote about Pegasus, the upside-down flying horse. Have you noticed the Great Square of Pegasus getting higher in the sky as the autumn season advances? If you can find Pegasus in the stars, you can find the constellation of Andromeda. And if you can find Andromeda, you can find something amazing; the farthest away object you can find with your unaided eye that is not a part of our Milky Way Galaxy, the Andromeda Galaxy. Read on to learn how to spot it! 

The Andromeda galaxy is a collection of about a trillion stars, 2.5 million light years  from Earth. Image credit:  Adam Evans [CC-BY-2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons

To find the constellation of Andromeda the Princess, first find the Great Square of Pegasus high in the east. Andromeda is marked by a bright line of stars extending out from the easternmost star in the square. See image below, set for Peoria at 8 PM.  

Find the Great Square of Pegasus high in the south at 8 PM.

Can you find Pegasus above? Andromeda is marked by the line of bright stars that extends away from the square of Pegasus. If you have trouble finding it, see the same image with constellation lines below.

Andromeda is marked by a line of four stars, starting with one corner of the square and extending toward the east. Image Credit: Stellarium.

If you look closely, you can see a second line of fainter stars above the bright line of stars in Andromeda. It is a fairly boring constellation, just two lines of stars. But what is really exciting is what you can find within the constellation: the Andromeda Galaxy!

If you are in a nice, dark , moonless sky (it will be difficult to spot the galaxy in the city) find the third star in the line of Andromeda, and find the fainter star above that (marked with a line in the above picture). If you look to a spot in the sky that looks empty just above that fainter star, and stare at it for a while, a small smudge of light should come into view. Actually, you will have better luck seeing it if you look slightly off center and use your peripheral vision. That tiny smudge of light is the combined light of a trillion stars - a whole galaxy! It is so far away, 2.5 million light years away, that in our sky we just see a faint smudge of light from the bright core. It is the only thing you can see in the sky without using a telescope that is not a part of our Milky Way Galaxy. 

The Andromeda galaxy is visible to the unaided eye in a dark sky, although it probably will not look as bright as in this image. Image Credit: EarthSky.org

 Zoom into the Andromeda galaxy in this video from the Hubble Space Telescope team!

The Andromeda galaxy is the closest large galaxy to the Milky Way, and is just one among the hundreds of billions of galaxies in the Universe, invisible to human eyes, but visible through our telescopes. Edwin Hubble's observation of a variable star in the Andromeda Galaxy is how he proved it was outside the Milky Way - that there are more galaxies in the Universe than our own. 

You can always learn what's up in the night sky at the Dome Planetarium at the Peoria Riverfront Museum. Stop in this holiday season to see Titanic: the Artifact Exhibition, and come to as many planetarium shows as you'd like in the day. Follow the us on Facebook or Twitter for daily updates.