M31 (Andromeda Galaxy)
The nearest spiral galaxy to the Milky Way.
M31, also known as the Andromeda Galaxy, is a spiral galaxy approximately 2.537 million light-years from Earth. It is the nearest galaxy to the Milky Way and is on a collision course with it, expected to merge in about 4.5 billion years. M31 is part of the Local Group of galaxies and contains approximately one trillion stars, making it the largest galaxy in our vicinity.
Key Facts
Distance from Earth
2.537 million light-years
Diameter
Approximately 220,000 light-years
Apparent Magnitude
+3.44 (visible to the naked eye)
Best Season for Viewing
Autumn (September to November)
Size in the Night Sky
Approx. 3 degrees, about 6 times the diameter of the full moon
Best Season
Autumn (specifically September to November) when it is highest in the sky during evening hours.
How to Find It
To locate M31, find the Great Square of Pegasus in the night sky. From the upper right star of the square, draw an imaginary line towards the left star of the square. The Andromeda Galaxy is located about 2.5 degrees in that direction, slightly up from the line.
Observing Tip
For optimal viewing, use a telescope with at least 4 inches of aperture. Avoid light pollution, and consider using a red flashlight to preserve your night vision. Use a long exposure setting for astrophotography to capture its details, and try stacking multiple exposures to enhance image quality.