Astronomers estimate that the presently observable universe contains about one hundred billion galaxies. These are very large groups of stars (see the 10/07/19 article by James Lewis) held together by gravity. They exist in difference shapes and can be spiral, elliptical, lenticular, or irregular.


Our own galaxy, the Milky Way, and its nearest full-size neighbor, the Andromeda galaxy, are both spiral galaxies. We used to think that the Andromeda galaxy was two to three times as large as our galaxy, but recent (2018) radio astronomy data shows that they are about the same size. The Andromeda galaxy is about two and one-half million light years away. Most galaxies appear to be moving away from us. Not so the Adromeda galaxy, which appears to be approaching us at a speed of about 400,000 kilometers per hour.


Even at this estimated distance and current speed, Andromeda will not collide with the Milky Way for another four to five billion years. This collision will eventually produce one large galaxy. This will not be an uncommon occurrence, since observational data shows that both the Andromeda galaxy and our Milky way have had a history of combining with and munching on smaller galaxies over the last several billion years.


Returning to the present, there are a couple of good ways to locate the Andromeda galaxy in the sky. First, find the W-shaped constellation of Cassiopeia high in the northeast sky in the evening this time of year. Counting from the right side of the W, visualize a line running from the third star to the second star and southerly away from the constellation. Follow this line with your eyes about two-thirds of the way to the next bright star (Alpheratz). A bit below this line you will see a faint blob of light about a sixth the size of the full moon. That blob is the Andromeda galaxy.


Another way is to locate the Great Square (in Pegasus) high in the night sky. Think of the four stars in the square as a baseball diamond with home plate roughly toward the southeast. Imagine a line from first base to third base and extending away from the square. This line generally points in the direction of the Andromeda galaxy, which can be seen at a slightly shorter distance past third base than that your eye traveled from first to third base. A pair of low-power binoculars may help.


Here is an interesting thought to consider: The Andromeda galaxy is the only object humans can see from “Earth with the unaided eye that is not in our own galaxy.