Measurements and an empirical model of the Zodiacal brightness as observed by the Solar Mass Ejection Imager (SMEI)

•SMEI measures Zodiacal brightness photometrically over most of the sky.•2854 daily maps, extending over 8.5 years.•Instrument above Earth's atmosphere, measurements less subject to contaminating light.•Empirical model presented which summarizes the measurements.•Annual average of Zodiacal brightness remains constant to ∼0.3% at nine sky locations over this time. The Solar Mass Ejection Imager (SMEI) provided near-full-sky broadband visible-light photometric maps for 8.5 years from 2003 to 2011. At a cadence of typically 14 maps per day, these each have an angular resolution of about 0.5º and differential photometric stability of about 1% throughout this time. When individual bright stars are removed from the maps and an empirical sidereal background subtracted, the residue is dominated by the zodiacal light. This sky coverage enables the formation of an empirical zodiacal-light model for observations at 1 AU which summarizes the SMEI data. When this is subtracted, analysis of the ensemble of residual sky maps sets upper limits of typically 1% for potential secular change of the zodiacal light for each of nine chosen ecliptic sky locations. An overall long-term photometric stability of 0.25% is certified by analysis of three stable sidereal objects. Averaging the nine ecliptic results together yields a 1-σ upper limit of 0.3% for zodiacal light change over this 8.5 year period.