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Andromeda Galaxy, also known as Messier 31, M31, or NGC 224, is a spiral galaxy approximately 780 kiloparsecs (2.5 million light-years) from Earth, and the nearest major galaxy to the Milky Way. Its name stems from the area of the sky in which it appears, the constellation of Andromeda.

The 2006 observations by the Spitzer Space Telescope revealed that the Andromeda Galaxy contains approximately one trillion stars, more than twice the number of the Milky Way’s estimated 200 to 400 billion stars. The Andromeda Galaxy, spanning approximately 220,000 light-years, is the largest galaxy in our Local Group, which is also home to the Triangulum Galaxy and other minor galaxies. The Andromeda Galaxy’s mass is estimated to be around 1.76 times that of the Milky Way Galaxy (~0.8-1.5×1012 solar masses vs the Milky Way’s 8.5×1011 solar masses). — Wikipedia

Andromeda (Encyclopædia Britannica)




Messier 31: The Andromeda Galaxy (Hubble’s Messier Catalog, NASA)
The Once and Future Stars of Andromeda (NASA Science)

Andromeda (Wolfram Alpha)




Melvil Decimal System # 523.112 Galaxies (Library Thing)
Library of Congress Subject Heading: Galaxies (Library Thing)

Library of Congress # QB856 Galaxies (UPenn Online Books)

WorldCat, Library of Congress, UPenn Online Books, Open Library




MERLOT: Multimedia Educational Resource for Learning and Online Teaching
OER Commons: Open Educational Resources


Andromeda (Astronomy Magazine)
Andromeda (



Andromeda Galaxy (


Here are links to pages about closely related subjects.

Knowledge Realm


Law (Constant) Relativity
Force Gravity, Electromagnetism (Light, Color)
Matter (Microscope) Molecule, Atom (Periodic Table), Particle

Universe (Astronomical Instrument)
Galaxy Milky Way, Andromeda
Planetary System Star, Brown Dwarf, Planet, Moon

Our Neighborhood
Solar System Sun
Terrestrial Planet Mercury, Venus, Earth (Moon), Mars
Asteroid Belt Ceres, Vesta
Jovian Planet Jupiter, Saturn, Uranus, Neptune
Trans-Neptunian Object
Kuiper Belt Pluto, Haumea, Makemake
Scattered Disc Eris, Sedna, Planet X
Oort Cloud Etc. Scholz’s Star
Small Body Comet, Centaur, Asteroid


1.   The resources on this page are are organized by a classification scheme developed exclusively for Cosma.