Balloon Measurements of the Far-Infrared Background Radiation

Measurements in five different passbands in the spectral region below 20 cm^-1 have been made with a liquid-helium-cooled radiometer in two flights at approximately 40-km altitude. The equivalent temperatures are 2.7^+0.4_-0.2, 2.8+/-0.2, 2.8+/-0.2, <=2.7, <=3.4°K in passbands of 1 to 5.4, 7.8, 7.9, 11.1, and 18.5 cm^-1. The results are consistent with a 2.7°K thermal radiation background. Atmospheric radiation of uncertain magnitude dominates the region above 11 cm^-1.