M31: The Great Andromeda Galaxy
| Catalogues | M31; NGC 224 | |
| Names | Great Andromeda Galaxy | |
| Type | Spiral Galaxy | |
| Constellation | Andromeda | |
| Season Visible in Evening | Autumn & Winter; Sept - Feb | |
| Conversation Notes | Large spiral galaxy near our own galaxy. Visible to the naked eye in dark skies, then the farthest object you can see. |
Galaxies are not easy to observe in small telescopes, and look nothing like the photos you have seen. You will not see colours or spiral arms, just a fuzzy patch of light. Even so, it is very impressive to see M31 when you realize you are seeing an object similar to our own galaxy, and located 2.9 Million Light-Years away from Earth. That is 27,434,000,000,000,000,000 kilometres. Since light travels at the speed of light (!) the light you are seeing when you look at M31 left there 2.9 million years ago - so you are seeing deep into the past.
M31 is such a large object that you need very low magnification to see it. If your telescope has a long focal length you will want your lowest magnification, widest-field eyepiece. You may even find it looks better in your finder scope. And it is easy to observe in binoculars, which you should certainly try, especially if you have a way to mount them on a tripod.
Finding M31
| Find the constellation Cassiopeia. It's shaped like a W, and is found on the other side of Polaris from the Big Dipper. It rotates around the sky with the seasons, so it may be upside down or on its end. |  |
| Note that the "W" is lopsided. One side forms a nice equilateral triangle, while the other side is distorted. We'll use the good, evenly balanced triangle as a pointer and as a measure. Note the distance across the base of the triangle - that will be our distance measure. |  |
| Use the triangle as a pointer, and mentally draw a line slightly more than 3 measures long, leading to the brightest star in that area. |  |
| This is Mirach, a bright star in the constellation Andromeda. |  |
Now go back toward Cassiopeia a short distance, and slightly off to the side away from the centre of the "W", to the next star you can see, slightly dimmer than Mirach. This is "Mu Andromeda". |
 |
Mentally draw a line from Mirach to Mu, and extend the line that distance again beyond Mu. |
 |
If you have very dark skies, you might be able to see the Galaxy at that point with your naked eyes, as a dim fuzzy patch of light. |
 |
Visible or not, point your telescope carefully to the end of the imaginary line from Mirach through Mu. |
 |
Switch to your magnifying finder if you have one. Hunt around this area, and find M31, a compact fuzzy patch of light. |
 |
Put your widest field (longest focal length) eyepiece in your telescope and look. Although it's just a fuzzy blob, you are seeing the bright core of a Galaxy - the combined light of over 100 Billion stars. You are seeing only the concentrated core - if you could see the spiral arms, the galaxy would be larger than the whole field of view. |
 |
If you have dark skies and a wide field of view, you will be able to detect two other galaxies, M32 and M110, as well. These are companions of M31, bound to it gravitationally and orbiting it. Depending on the time of year, your orientation, and your optics, they may not be oriented as shown in this simulation. |
 |
Aren't galaxies supposed to be swirls of amazing colours? Not when viewed with your eyes - here is an explanation.
All the above images were generated with Starry Night Pro.