The Andromeda Galaxy, about two and a half million light years away, is the most distant object that can be seen with the unaided eye. The evening hours of late fall offer prime viewing opportunities for locating both the galaxy and the constellation with which it is identified.
The constellation Andromeda takes its name from the heroine of a Greek story. According to the tale, Andromeda's mother, Queen Cassiopeia, was the wife of King Cepheus, who ruled over a coastal kingdom. Cassiopeia ran afoul of Poseidon, the sea God. Her crime involved upsetting the Nereids, a group of sea nymphs known for their beauty. Cassiopeia bragged that Andromeda was more beautiful (in some tellings, Cassiopeia bragged that it was she herself who was more beautiful). The upset Nereids complained to Poseidon, so he unleashed a sea monster against King Cepheus's kingdom. After many coastal communities experienced much ravaging, Cepheus sought advice from an oracle about how to appease Poseidon. He was told to sacrifice his daughter to the monster by chaining her to a rock at the edge of the sea. In desperation, he followed the instructions. Fortunately for Andromeda, a hero intervened. Perseus, who was on his way home from saving other folks from Medusa, saw Andromeda and instantly fell in love. He rescued her and the two were promptly married and lived happily (sort of) ever after.
The stars in these two images are the same as those in the field shown above. Constellation lines have been added to the first to help you identify the Great Square, Cassiopeia, Andromeda, and Perseus. The arrows in the second image point to the location of the Andromeda Galaxy. (Images by Karen Bellenir based on a star field generated with Stellarium 0.13.2 with permission made available under the GNU General Public License.)
To find Andromeda in the sky during November, look up after the sky is fully dark. See if you can find four similarly bright stars that make a squarish shape. This is an asterism known as the Great Square. Andromeda's head lies at one of these points, and you can trace the rest of her body, including her outstretched and chained arms, by connecting a series of dimmer stars.
If your sky is sufficiently dark, you may also be able to see the Andromeda Galaxy as a faint smudge beside Andromeda's waist. You can pinpoint the location by following the A-shaped double line of stars that extend from the corner of the Great Square. Look above the second pair. You can also use the constellation Cassiopeia as a guide. Cassiopeia looks like a lazy W in the sky. If you use the sharpest V of the W as an arrow, it will point to the galaxy.
For More Information
If you want a detailed sky map, visit SkyMaps.com. Be sure to choose the one for your hemisphere and latitude.
You can see x-ray images of deep sky objects in Andromeda and read more about the mythology in "Andromeda," from the Chandra X-Ray Observatory.
If you'd like to share the joy of stargazing with your children or grandchildren, Pier Press recommends two classics by H. A. Rey: The Stars: A New Way to See Them for young people ages 12 and up, and for younger children, Find the Constellations. For more information, see our review in Pier Perspectives or visit the Pier Press® Bookstore.
This article originally appeared in the November 2015 issue of Observations: A Pier Press® Newsletter. You can access the archived issue here, and if you're not already a subscriber, click here to sign up. It's free.