An Ancient Universe: How Astronomers Know the Vast Scale of Cosmic Time


The Andromeda Galaxy

The Andromeda Galaxy. The closest large galaxy to us is called the Andromeda Galaxy, for the constellation in which it is found. It is a large spiral-shaped collection of stars about 2.2 million lightyears from us in other words, light takes 2.2 million years to reach us from this galactic neighbor. The area of the sky covered in this image is more than five times the area of the full moon. (Courtesy of T.A. Rector and B.A. Wolpa, National Optical Astronomy Observatories/AURA/NSF)

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