CMB temperature map & early universe
Hover for temperature · Click to measure a spot
The CMB is thermal radiation from ~380,000 years after the Big Bang, when the universe cooled enough for atoms to form (recombination). Originally ~3000 K, it has redshifted to 2.725 K today — the most perfect blackbody spectrum ever measured. Tiny temperature fluctuations (~1 part in 100,000) are the seeds of all cosmic structure.