Andromeda Galaxy (M31)
The Nearest Spiral Galaxy to the Milky Way
The Andromeda Galaxy, designated as M31, is a spiral galaxy approximately 2.537 million light-years from Earth. It is the closest galaxy to our Milky Way and is on a collision course with it, expected to merge in about 4.5 billion years. M31 contains over a trillion stars, more than double the number in the Milky Way.
Key Facts
Distance from Earth
Approximately 2.537 million light-years
Diameter
About 220,000 light-years
Apparent Magnitude
+3.44 (visible to the naked eye)
Visibility
Visible year-round in the Northern Hemisphere, best in fall
Best Viewing Time
Late summer to early winter, around September to November
Best Season
Best viewed in the Northern Hemisphere during autumn months (September to November).
How to Find It
Look for the constellation Andromeda. The galaxy is located about 2.5 degrees from the star Alpheratz (the brightest star in Andromeda). From the Great Square of Pegasus, move along the line of stars toward Andromeda.
Observing Tip
Use binoculars or a small telescope to get a clearer view of M31. Astrophotographers should use longer exposure times and consider stacking images for better detail, as M31 is wide, and capturing its entire structure requires a wider field of view.