Far-infrared surveys of the sky

A series of far-infrared surveys of the sky is searching for thermal radiation from interstellar grains and for other localized sources of far-infrared radiation. A balloon-borne germanium bolometer, cooled by liquid helium, is used in association with a telescope and spectral filters. During two initial flights the response to a black-body source was mainly between 300 and 360 microns. Approximately half the celestial sphere was surveyed, including most of the northern Milky Way. The angular resolution was 2 degrees. Moon was the only source of thermal radiation detected. The upper limit on the differential flux, relative to background, from other sources was 2 x 10(-23) watt per square centimeter per hertz, corresponding to an antenna temperature of 0.6 degrees K in the Rayleigh-Jeans approximation, or 10 degrees K for a black body.     

Far-infrared observations of the night sky

We have flown a telescope cooled to liquid-helium temperatures and made far-infrared observations of the night sky. A gallium-doped germanium detector, sensitive from 5.2 to 130 micrometers, detected a minimum signal of 10(-9) watt per square centimeter per steradian referred to 100 micrometers. The origin of this signal can be instrumental, atmospheric, interplanetary, or interstellar. We can place a firm upper limit on the color temperature of a dilute cosmic background flux.