Cosmic Microwave Background Radiation (CMB) is relic [[Electromagnetic Radiation]] from the early universe.

It was released when the universe cooled enough for atoms to form and photons could travel freely (roughly 380,000 years after [[The Big Bang]]).

Because of [[expansion of the universe]], that ancient light has been stretched into the microwave range.

## Why it matters
The CMB is one of the strongest observational pillars behind modern cosmology.

## See also
- [[The Big Bang]]
- [[expansion of the universe]]
- [[Electromagnetic Radiation]]