Cosmic microwave background radiation. Computer illustration showing spherical maps of cosmic microwave background (CMB), the thermal radiation left over from the Big Bang. These maps show the light emitted by the Cosmos only 380,000 years after the Big Bang during the recombination epoch, when photons decoupled from matter and travelled freely through the space for first time. Here, the colours show tiny variations in the temperature (anisotropies) of the early universe.