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Abell 1689 cluster of galaxies. Photo courtesy of NASA. Public domain.

Big Bang Theory: The hypothesis that all matter and energy were at one time compresses into a very small volume; then there was an explosion that sent everything moving outward, causing the universe to expand.

Blueshift: Shift of wavelengths of light towards the blue end of the spectrum; happens as a light source moves toward us.

Galaxy: A collection of billions of stars.
Redshift: Shift of wavelengths of light towards the red end of the spectrum; happens as a light source moves away from us.
Universe: Everything that exists; all matter and energy; also includes all of space and time.
Last modified: Saturday, 24 April 2010, 9:27 AM