M31 (Andromeda Galaxy)
The closest spiral galaxy to our Milky Way.
M31, also known as the Andromeda Galaxy, is the nearest spiral galaxy to the Milky Way and is on a collision course with our galaxy. It is part of the Local Group of galaxies, which includes the Milky Way, the Triangulum Galaxy, and about 54 other smaller galaxies. M31 is visible to the naked eye from Earth under dark skies as a faint, glowing patch. It is an enormous galaxy, containing about one trillion stars, and it holds many secrets about the formation and evolution of galaxies.
Key Facts
Distance from Earth
Approximately 2.537 million light-years
Diameter
About 220,000 light-years
Apparent Magnitude
Approximately 3.44 (naked-eye visible)
Visibility
Can be seen with the naked eye in dark skies.
Best Viewing Season
Fall (September to November) in the Northern Hemisphere.
Ideal Viewing Time
After sunset and before midnight, when it is highest in the sky.
Best Season
Best viewed in Fall (September to November) in the Northern Hemisphere.
How to Find It
To locate M31, find the constellation Andromeda. Look for the 'W' shape of Cassiopeia, which is directly opposite Andromeda. Draw an imaginary line from the left star of the 'W' through the middle star to a point in the sky. M31 is roughly in that direction, and you can trace from the two stars at the top of the 'W' towards an area that lies between the two. M31 is around 2 degrees long, stretching from the star Mirach (beta Andromedae) to the region around the galaxy.
Observing Tip
To enhance visibility, use binoculars or a small telescope. Averted vision (looking slightly off to the side) can help in spotting the galaxy more clearly. For astrophotographers, using a longer exposure time can reveal structure and detail in the galaxy. A tracking mount will help keep the image steady during long exposures, allowing the details of the galaxy to stand out.