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M. G. Hauser (STScI)
The cosmic infrared background (CIB) radiation has been a long-sought fossil of the cosmic "dark ages" when pre-galactic, protogalactic, and galactic systems formed and evolved. The infrared spectral range is important because the mechanisms of cosmic red-shift and dust absorption and re-emission shift energy emitted at ultraviolet and optical wavelengths into the infrared. The COBE Diffuse Infrared Background experiment (DIRBE) was designed to search for the CIB from 1.2 to 240 \mum wavelength, and the COBE Far Infrared Spectrophotometer (FIRAS) extended this coverage to millimeter wavelengths. After removal of the bright foreground contributions from the solar system and Milky Way galaxy, the DIRBE sky maps reveal the CIB at 140 and 240 \mum and provide upper limits at shorter wavelengths. The FIRAS data yield consistent results in the far infrared, and extend the CIB detection to longer wavelengths. The COBE measurements show that there is more energy in the CIB from far-infrared to millimeter wavelengths than in the integrated light from galaxies from UV to near-infrared wavelengths: the Universe had a luminous but dusty past.