Tis the season to search for the most distant object that the human eye can see unaided – the Andromeda Galaxy, or Messier 31. This large spiral galaxy is a big sister to our own galaxy, the Milky Way. It is 2.5 million light-years from our Sun, which means that the light from its stars has been traveling the entire time. And if extraterrestrial astronomers live there and look at us, they see our solar system as it looked 2.5 million years ago!
Where is the Andromeda Galaxy in the night sky?
In mid-September, the Andromeda Galaxy is just under halfway up in the east-northeast sky at 9:00 PM local time. (It will be higher later.) To find it, first find the medium-luminosity star Mirach. It is the second star when jumping to the left of Alpheratz, which marks the eastern corner star of the great square Pegasus. Next, look for a fainter star shining a few finger widths above Mirach. The Andromeda galaxy is even higher at this same distance. You can also use the three stars that form the right “V” in the constellation Cassiopeia, shaped like a “W”. They form an arrow pointing directly at M31.
How to find the Andromeda Galaxy with the naked eye?
Under dark skies, using only your unaided eyes, you should be able to see a faint blur extending from left to right. Try to direct your attention a little further away from the galaxy and it will clear up – the trick of side vision! The galaxy spans six full moon diameters across the sky, but only its bright core and surrounding inner halo are usually visible. The galaxy is quite easy to see with binoculars. The giant galaxy is a cool object to see!
How to see the Andromeda galaxy in a telescope?
Since telescopes have fields of view too narrow to see the entire galaxy, they will usually only show you the bright core of Andromeda. As you watch, see if you can make out the two fuzzy-looking small companions of M31, the small elliptical galaxies called M32 and M110. M32 is closer to the nucleus of the main galaxy and is located just to the lower right. M110 sits above the main core and is slightly further away. At 2.49 million light-years away, M32 is closer to us than the Andromeda galaxy, while M110 is 200,000 light-years further away. (Most telescopes face and/or reflect these directions).
How to find Andromeda Galaxy with stargazing apps?
The easiest way to find the Andromeda Galaxy is to use a star finder app. How to find the Andromeda Galaxy in Sky Tonight:
- Tap the magnifying glass icon in the lower left corner of the main screen.
- Type “Andromeda Galaxy” in the search field.
- Click on the corresponding result to learn more about the galaxy.
- Tap the blue target icon in the lower right corner of the screen: the app will show you the location of the Andromeda galaxy.
- Tap the blue compass icon in the lower right corner and move your device by following the white arrow to find the Andromeda galaxy in the sky above you.
Triangle Galaxy (M33) – the second Messier object to observe in September
Another large galaxy, called Messier 33 in Triangulum, is 2.75 million light-years away. Observers with very sharp eyes, under very dark sky conditions, can sometimes see it too – setting a record. This galaxy is all the more difficult to observe as it is oriented almost towards the Earth. Its light is therefore spread over a large area of the sky (equivalent to 1.5 diameters of the full moon), making it generally dimmer. It sits just 1.3 fist diameters below M31, a palm width below the Mirach star. Images and sky maps showing both galaxies are available here.
About the author: Chris Vaughan, aka @astrogeoguy, is an award-winning astronomer and earth scientist based near Toronto, Canada. He is a fellow of the Royal Astronomical Society of Canada and operator of the historic 74˝ telescope at the David Dunlap Observatory. Chris writes for SkyNews magazine and Space.com and has his own weekly Astronomy Skylights blog, which is read worldwide.