Celestial Reasonings

Abstract. Observations of the Moon from an observatory designed and operated specifically for determination of absolute lunar photometry have been used to develop a spectral irradiance model of the Moon covering 340-2430 nm appropriate for calibration of Earth-orbiting spacecraft. An empirical model of irradiance has been developed that treats phase and libration explicitly, with absolute scale founded on photometry of the star Vega and the spectra of returned Apollo samples. This model has the same form at each wavelength, with 18 coefficients, 8 of which are constant across wavelength, for a total of 328 coefficients. Over 1000 lunar observations are fitted at each wavelength; the average residual is less than 1%. The irradiance model is actively being used in lunar calibration of several spacecraft instruments, and can track senso