In astronomy, the cosmic light horizon is a "horizon" which marks the edge of the visible universe. This horizon is the edge of a sphere, centered upon the Earth, which is approximately 13.7 billion light years in radius; this figure is sometimes referred to as the "lookback distance" (because astronomers, who view distant objects, are "looking back" into the history of the universe -- see: speed of light). The general homogeneity of temperatures, at the edge of the cosmic horizon, is part of the evidence for the "Big Bang".
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