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Find the Andromeda galaxy on dark autumn nights

09oct17_430

Tonight for October 15, 2014

Tonight … find the Andromeda galaxy. The large square pattern on today’s chart is the Great Square in the constellation Pegasus. The constellation Andromeda can be seen as two streams of stars extending from one side of the Square, beginning at the star Alpheratz.

I learned to find the Andromeda galaxy by star-hopping from the Great Square to the two stars marked here – first Mirach, then Mu Andromedae. An imaginary line drawn through these two stars points to the Andromeda galaxy. You can also find the Andromeda galaxy using the constellation Cassiopeia.

Just be aware – bright moonlight or city lights can overwhelm the faint glow of this object. The single most important thing you need to see the galaxy is a very dark sky.

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The Andromeda galaxy (upper right of photo) as seen by EarthSky Facebook friend Ted Van at a Montana campsite in mid-August 2012. Thank you, Ted! Click here to expand image.

What does the galaxy look like to the eye? Assuming you have a dark sky, it appears as a large fuzzy patch – bigger than a full moon in the sky – but vastly fainter and more subtle.

For binocular astronomers: The Andromeda galaxy is the most distant thing you can see with your eye alone. Binoculars, as always, enhance the view. Binoculars are an excellent choice for beginners to observe the Andromeda galaxy, because they are so easy to point. As you stand beneath a dark sky, locate the galaxy with your eye first, then slowly bring the binoculars up to your eyes so that the galaxy comes into binocular view. If that doesn’t work for you, try sweeping the area with your binoculars. Go slowly, and be sure your eyes are dark-adapted. The galaxy will appear as a fuzzy patch to the eye. It’ll appear brighter in binoculars. Can you see that its central region is more concentrated?

With the eye, or with binoculars, or even with a backyard telescope, the Andromeda galaxy won’t look like the image below. But it will be beautiful. It will take your breath away.

Image of the Andromeda galaxy captured by NASA's Wide-field Infrared Survey Explorer. Image Credit: NASA/JPL-Caltech/UCLA

One of you wrote, I’ve heard that the Andromeda galaxy will someday collide with our galaxy! Is that still a definite possibility? Actually, “definite possibility” describes much of what we know – or think we know – about the universe. As for the Andromeda galaxy and its future collision with our Milky Way – the first attempt to measure the radial velocity of this galaxy (its motion forward or back, along our line of sight) was made in 1912. After that, astronomers believed for some decades that the galaxy was approaching at nearly 300 kilometers per second, but later astronomers disagreed.

Then in May 2012, NASA astronomers announced they can now predict the time of this collision of titan galaxies with certainty. Remember, though, that the Andromeda Galaxy is 2.2 million light-years away, with a single light-year being almost 10 trillion kilometers. So although it does appear that this galaxy is approaching our Milky Way galaxy … it’s nothing to lose sleep over. When will they collide? According to NASA astronomers in 2012, it’ll be four billion years from now.

Read more: Will the Milky Way and Andromeda galaxies collide someday?

Plus when galaxies collide, they don’t exactly destroy each other. Because there’s so much more space than stars in our universe, colliding galaxies pass through each other, like ghosts. But they do interact. Check out this cool video: Night sky as Milky Way and Andromeda galaxies merge.

Bottom line: The Andromeda galaxy, aka M31, will be visible on dark, moonless evenings from now until the beginning of spring. This post tells you how to use the constellation Pegasus to find it. Be sure you’re looking on a moonless night, far from city lights. This galaxy is approaching our Milky Way galaxy, across the vastness of space. Astronomers say that – four billion years from now – our two galaxies will collide.

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