Celestial infrared calibration sources in the 8-14 micrometer region

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Venus and Jupiter are often used as long wavelength infrared (LWIR) calibration sources. The authors have reviewed the literature on radiometric and spectrometric measurements of these two planets and adopted reasonable brightness temperatures and spectral dependencies for their thermal radiation. Using these data, irradiance coefficients that can be used to determine the irradiance reaching the earth from these planets at any time were calculated. A crucial factor in the utility of these planets as calibration sources is the constancy with which they radiate in the infrared. The authors conclude that Jupiter may be a variable source. Venus, on the other hand, appears to be generally quite constant, but brief temporal variations may take place.