"The Galaxy," or "our galaxy," or, most often, "the Milky Way," is a pale band of light in the night-time sky. You can see it if the sky is clear and dark. It is really made of billions of stars. The sun, the earth, and the solar system are all inside our galaxy. "A galaxy" means one of the billions of galaxies similar to ours. "Galaxy" is derived Greek word meaning "milk." The Galaxy, as it appears in the night time sky: https://upload.wikimedia.org/wikipedia/commons/c/c6/Milky_Way_Night_Sky_Black_Rock_Desert_Nevada.jpg A famous galaxy, the Great Nebula in Andromeda: http://stars.astro.illinois.edu/arc/m31-mkr.jpg

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