Cosmic microwave background
Cosmic microwave background is electromagnetic radiation observed throughout the universe with a nearly uniform temperature. It is interpreted as a remnant of an early, hot phase in cosmic evolution.
The cosmic microwave background is discussed in cosmology, astrophysics, and observational astronomy.
Status
The cosmic microwave background has been measured with increasing precision by ground-based and space-based instruments. Its temperature fluctuations and polarization patterns are used to constrain cosmological models.