Spectrum of the Cosmic Background Radiation

New measurements of the emission spectrum of the night sky have been made in the frequency range from 1.7 to 40 ${\mathrm{cm}}^{\ensuremath{-}1}$ using a fully calibrated, liquid-helium-cooled, balloon-borne spectrophotometer. The results show that the spectrum of the cosmic background radiation peaks at 6 ${\mathrm{cm}}^{\ensuremath{-}1}$ and is approximately that of a 3-K blackbody out to several times that frequency. However, the data show deviations from a simple blackbody curve.