Andromeda

by Shaphan Shank | Dec 1, 2023 | 0 comments

Andromeda Galaxy M31
Andromeda Galaxy, M31. Photo © Shaphan Shank.

Andromeda is one of those ideal constellations that is easy to find, and that contains a wide variety of outstanding telescopic targets. The main part of Andromeda is a curving line of stars that extends to the northeast from the northeastern corner of the Great Square of Pegasus. On star maps, the constellations Andromeda and Pegasus are connected at Alpheratz, the star marking the northeastern corner of the Great Square of Pegasus.

The Andromeda Galaxy (M31) is by far the most famous deep sky object in Andromeda, and for good reason. This galaxy is the nearest galaxy to the Milky Way, and, as a result, it is the largest and brightest galaxy in the sky (except for a couple of small satellite galaxies of the Milky Way). To find M31, start at Alpheratz and follow the figure of

Andromeda northeast to Mirach, the second star out from Alpheratz. Two evenly spaced stars form a short (~7°) line that points northwest from Mirach. M31 is right beside the second star at the northwestern end of this line of stars.

Under dark skies, M31 is easily visible to the unaided eye as a fuzzy oval of light. Binoculars don’t reveal much detail in the galaxy except for its bright core, but they do make it appear much larger and brighter. With careful observation, you may even be able to find the two companion galaxies of M31: M32 and M110. However, these two galaxies are much easier to see with a telescope.

At first glance, the telescopic view of M31 may just look like a larger, brighter version of the view through smaller instruments. However, if you look closely, you should be able to see some subtle details with a mid-sized telescope. The most obvious structure in M31 is a dark dust lane which lies northwest of the core of the galaxy.

Telescopes show M32 as a little bright spot on the southeast side of M31. M110 lies a little farther from M31 on the opposite side as M32; this galaxy is a little larger, fainter, and more elongated than M32.

One of the lesser-known objects in Andromeda is a small galaxy called Mirach’s Ghost, or NGC 404. The special thing about this galaxy is not its own appearance, but its location. Mirach’s Ghost lies just 7 arcminutes (a little over 0.1°) from the star Mirach. When viewed through a telescope, the dim little galaxy looks almost like a glare caused by the striking yellow-orange glow of nearby Mirach. The combination of the bright star and the fuzzy little galaxy is a unique and memorable sight. Try both low and high magnification; neither one is really “right” or “wrong” for this target.

Almach, the star that marks the northeastern end of Andromeda, is one of my favorite double stars, rivalling Albireo as one of the most vividly colored pairs in the sky. The component stars of Almach, like Albireo, are gold and blue. However, Almach is a much tighter double than Albireo (10 arcseconds vs. 34 arcseconds), and its primary is a bit brighter than Albireo’s. In my opinion, both of these factors give Almach an edge over Albireo. I like using fairly low magnification to split this double. Doing so keeps the components close together, emphasizing their contrasting brightness and color.

NGC 752 is the largest and brightest of the open star clusters in Andromeda. This cluster lies about 5° south-southwest of Almach. NGC 752 is quite large, and, as a result, it makes a good binocular target. Binoculars will show the cluster as a round, hazy patch, with a few stars just bright enough to be resolved. Telescopes will resolve dozens of stars in the cluster, but be sure to keep the magnification very low in order to fit the entire cluster into your field of view.

To round out its collection of deep sky objects, Andromeda contains a fine planetary nebula, NGC 7662 (popularly known as the Blue Snowball Nebula). To find this nebula, first look for a short (~3°) curving line of stars about 15° north of the Great Square of Pegasus. (For comparison, the Great Square itself is about 15° across.) The southernmost star in this curving line is Iota Andromedae. NGC 7662 is about 2° west of this star. NGC 7662 is quite bright, but, like most planetaries, it is also small. A mid-sized telescope at high magnification will show this nebula as a little bluish disk with a slightly darker center.

Star map of Andromeda

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