An Etymological Dictionary of Astronomy and Astrophysics

Thermal radiation with a temperature of 2.73 K that is apparently uniformly distributed in the Universe. It is believed to be a redshifted remnant of the hot radiation that was in thermal equilibrium with matter during the first hundred thousand years after the Big Bang. Same as → cosmic microwave background (CMB) radiation.

See also: → microwave; → background;
→ radiation.