The cosmic neutrino background ( CNB ) consists of low-energy relic neutrinos which decoupled from the cosmological fluid at a redshift z \sim 10 ^ { 10 } .
Despite being the second-most abundant particles in the universe , direct observation remains a distant challenge .
Based on the measured neutrino mass differences , one species of neutrinos may still be relativistic with a thermal distribution characterized by the temperature T \sim 1.9 K. We show that the temperature distribution on the sky is anisotropic , much like the photon background , experiencing Sachs-Wolfe and integrated Sachs-Wolfe effects .