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Looking Up column: Find the Andromeda galaxy

Peter Becker
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The Andromeda Galaxy, M31. The bright spot along its lower edge is satellite galaxy M32; above M31 as seen here is its satellite, M110. A small telescope will show the satellites. [Photo by Parker Bossier (Own work) [CC BY-SA 4 (https://creativecommons.org/licenses/by-sa/4)], via Wikimedia Commons]

The next clear evening, before the bright moon washes out the fainter stars, take a look for the Andromeda galaxy. Unless you have significant light pollution, you should be able to see it high in the sky with your eyes alone.

It is the farthest you can easily see without the aid of binoculars or a telescope. You are actually looking at a spiral galaxy twice the span of the Milky Way spiral in which we live.

To the naked eye, the Andromeda Galaxy, also referred to as M31 (it’s old nickname was the “Great Nebula”), appears as a fuzzy ellipse. The darker your sky, the better.

M31 shines at magnitude +3.44. A star of that magnitude is more easily seen, as the light from M31 is spread out rather than constrained to a point source, which is essentially how individual stars appear to us.

In mid-November, at around 9:30 p.m. from mid-northern latitudes, M31 is almost at the zenith - the point directly overhead. If you deal with light-polluted skies, the area around the zenith is usually the best choice as it is darkest.

At 8 p.m., M31 is high in the southeast. To locate the galaxy, start with the “Big M.”

The constellation Cassiopeia, high in the northeast on November evenings, is easy to recognize. Its five principal stars form a letter “M” pattern (or “W” when oriented that way). The “M” will be on its side, at this time, the bottom of the “M” facing right.

To find the Andromeda galaxy, start with the top bend of the “M” in Cassiopeia; think of these three stars as an arrowhead, pointing to the right. This “arrowhead” points roughly right at the galaxy.

M31 is about 15 degrees from Cassiopeia. That is about the length of the “M” of Cassiopeia from end to end.

The galaxy is within the constellation Andromeda; there are actually many galaxies in this part of the sky within reach of a small- to moderate-size telescope, but M31 is the brightest and most famous.

If your sky is dark, look for the faint Milky Way Band, in the background of Cassiopeia and stretching east to west-southwest on a November evening.

It always thrills me to look at the Milky Way Band in this part of the sky, and the Andromeda Galaxy to the right, at the same time.

The hazy, billowing Milky Way Band is actually the spiral arms of our home galaxy, filled with stars, dust and gas. The sun is located right within the pancake shape (with a big “lump” in the center) of the Milky Way galaxy, so we are looking at it from inside.

Spiral galaxies spread across the heavens are all oriented their own way. We see some in our telescopes and deep-sky photographs in a flat, “edge-on” perspective, some as circles, “straight-on” and others as ellipses, between “edge-on” and “straight-on.”

With our naked eyes, we can view the Milky Way galaxy “edge-on” from inside and the Andromeda galaxy oriented as an ellipse.

Binoculars will give you a fine view of the Andromeda galaxy. Notice the bright, central “hub” and the fainter, hazy ellipse on either side. The outer portion away from the hub are the spiral arms of the galaxy blended together.

A small telescope, of even 3 inches aperture (larger is even better) will show you not only Andromeda Galaxy, bigger and brighter, but also two small satellite galaxies that orbit it. One of them, M32, appears round and fuzzy, seemingly touching one side; the other one, M110, is dimmer and elliptical, on the other side from M32 and separated more from the main galaxy.

The Milky Way also has several smaller satellites. The brightest, the Large Magellanic Cloud and Small Magellanic Cloud, appear to the naked eye like detached pieces of the Milky Way Band. Unfortunately for us northerners, they can only be viewed in the far southern sky, as seen from below the equator.

Our neighbor, the Andromeda galaxy, M31, is approximately 2.54 million light-years from here. That is how long it took for the collective light of the galaxy’s billions of stars to reach our eyes.

There are roughly one trillion stars in M31, about twice as many as in the Milky Way. Astronomers now suspect that most stars have a system of planets. One can only imagine the worlds unseen!

The Milky Way and Andromeda galaxies are actually on a collision course. At the current rate, they are expected to merge as one in 4.5 billion years.

M31 is approaching even as you read this, but is so very distant, our descendants won’t tell a difference in its apparent size and brightness for a very long time.

Not far away in the night sky is the spiral galaxy M33, in Triangulum the Triangle. M33 is a little farther, 2.73 million light-years. At magnitude +5.72, M33 can also be glimpsed with the unaided eye from very dark sites. It is not nearly as easy to see as Andromeda!

Both of these galaxies and the Milky Way are part of the “Local Group” of galaxies, traveling the universe together.

New moon is on Nov. 15.

Keep looking up at the sky!

Peter Becker is managing editor at The News Eagle in Hawley, Pennsylvania. Notes are welcome at news@neagle.com. Please mention in what newspaper or website you read this column.

This star chart identifies the Andromeda galaxy by its old nickname, the "Great Nebula." Cassiopeia is below.