A preliminary measurement of the cosmic microwave background spectrum by the Cosmic Background Explorer (COBE) satellite

We present a preliminary spectrum of the background radiation between 1 and 20 cm^-1^ (1 cm to 0.5 mm wavelength) from regions near the north Galactic pole, as observed by the FIRAS instrument on the COBE satellite. The spectral resolution is 1 cm^-1^. The spectrum is well fitted by a blackbody with a temperature of 2.735 +/- 0.06 K, and the deviation from a blackbody is less than 1% of the peak intensity over the range 1-20 cm^-1^. These new data show no evidence for the submillimeter excess previously reported by Matsumoto et al. in 1988 in the cosmic microwave background. Further analysis and additional data are expected to improve the sensitivity to deviations from a blackbody spectrum by an order of magnitude.