PHOTOEMISSIVITY IS ONE OF THE FUNDAMENTAL PROPERTIES OF THE LUNAR REGOLITH. THE PHOTOELECTRIC PROPERTIES OF THE LUNAR SURFACE ARE PARTICULARLY RELEVANT TO THE ELECTROSTATIC ENVIRONMENT ON THE MOON'S DAYSIDE BECAUSE THE CURRENT BALANCE OF THE EMITTED PHOTOELECTRONS AND INCOMING ELECTRONS IS THE PRIMARY FACTOR CONTROLLING LUNAR SURFACE CHARGING. THE RESULTING SURFACE POTENTIAL DETERMINES THE DYNAMICS OF CHARGED DUST GRAINS AND IONIZED CONSTITUENTS OF THE TENUOUS LUNAR ATMOSPHERE. IN PARTICULAR THE HIGH-ENERGY PART OF THE PHOTOELECTRON SPECTRUM IS CRITICAL FOR DETERMINING SURFACE POTENTIALS IN LOW-PLASMA-DENSITY CONDITIONS (E.G. IN THE TERRESTRIAL MAGNETOTAIL LOBES). DESPITE ITS IMPORTANCE THE PHOTOELECTRIC YIELD OF THE LUNAR SURFACE FOR HIGH-ENERGY (>20 EV) SOLAR PHOTONS REMAINS UNDETERMINED LIMITING OUR ABILITY TO CHARACTERIZE AND ASSESS THE ELECTROSTATIC PROPERTIES AT VARIOUS SURFACE LOCATIONS INCLUDING POTENTIAL LANDING SITES IN ALL AMBIENT PLASMA CONDITIONS THAT THE MOON ENCOUNTERS. TO IMPROVE OUR KNOWLEDGE AND UNDERSTANDING OF REGOLITH PROPERTIES AND THE LUNAR ELECTROSTATIC ENVIRONMENT WE NEED TO ANSWER THE FOLLOWING QUESTIONS: (I) WHAT ARE THE PHOTOELECTRIC PROPERTIES OF THE LUNAR REGOLITH FOR HIGH-ENERGY SOLAR PHOTONS? (II) WHAT IS THE TEMPORAL AND SPATIAL VARIABILITY OF THE ELECTROSTATIC ENVIRONMENT ON THE SUNLIT LUNAR SURFACE IN VARYING SOLAR AND PLASMA CONDITIONS? AND (III) HOW DOES THE LUNAR ELECTROSTATIC ENVIRONMENT INFLUENCE LUNAR EXOSPHERIC PICKUP IONS AND SURFACE WEATHERING? WE AIM TO ANSWER THESE QUESTIONS BY COMBINING PUBLICLY AVAILABLE PLASMA MEASUREMENTS FROM THE ACCELERATION RECONNECTION TURBULENCE AND ELECTRODYNAMICS OF THE MOON'S INTERACTION WITH THE SUN (ARTEMIS) MISSION AND SOLAR EXTREME ULTRAVIOLET (EUV) FLUXES FROM THE SOLAR DYNAMICS OBSERVATORY (SDO) MISSION AND THE OBSERVATION-BASED FLARE IRRADIANCE SPECTRAL MODEL (FISM). THE DUAL-PROBE ARTEMIS MISSION CONDUCTS COMPREHENSIVE PLASMA AND ELECTROMAGNETIC FIELD MEASUREMENTS WITH SPACECRAFT POTENTIAL INFORMATION ENABLING OBSERVATIONS OF THE HIGH-ENERGY DISTRIBUTION OF LUNAR PHOTOELECTRONS ESCAPING FROM THE SUNLIT LUNAR SURFACE ALONG THE MAGNETIC FIELD LINE WITH CLEAR SEPARATION OF LUNAR PHOTOELECTRON SPECTRA FROM SPACECRAFT PHOTOELECTRON CONTAMINATION. COMBINATION OF CLEAN ACCURATE LUNAR PHOTOELECTRON SPECTRA OBTAINED BY ARTEMIS WITH SIMULTANEOUS DIRECT EUV MEASUREMENTS BY SDO WHICH CAN BE COMPLEMENTED BY FISM FOR<6 NM WAVELENGTHS ALLOWS US TO DERIVE THE PHOTOELECTRON YIELD FOR APPROXIMATELY 20-1000 EV PHOTONS. ONCE THE PHOTOELECTRON YIELD IS DETERMINED WE CAN CALCULATE THE EQUILIBRIUM POTENTIAL OF THE LUNAR SURFACE FOR A GIVEN INPUT SOLAR SPECTRUM AND AMBIENT ELECTRON FLUX. WITH THE ABILITY TO DERIVE THE DAYSIDE LUNAR SURFACE POTENTIAL FOR A WIDE RANGE OF PLASMA PARAMETERS AND SOLAR SPECTRA WE CAN STUDY THE TEMPORAL VARIABILITY OF THE LUNAR ELECTROSTATIC ENVIRONMENT IN RESPONSE TO SUBSTANTIAL CHANGES IN THE AMBIENT PLASMA AND SOLAR CONDITIONS (E.G. TERRESTRIAL MAGNETOTAIL CROSSINGS AND INTENSE SOLAR FLARES). FURTHERMORE BY COMPARING PHOTOELECTRON ENERGY SPECTRA OBTAINED AT MAGNETIZED AND UNMAGNETIZED REGIONS WE CAN INVESTIGATE SURFACE POTENTIAL MODIFICATION BY CRUSTAL MAGNETIC FIELDS WHICH WERE FIRST SUGGESTED BY THE APOLLO MEASUREMENTS. FINALLY WE CAN USE THIS ENHANCED KNOWLEDGE OF THE LUNAR ELECTROSTATIC ENVIRONMENT TO FURTHER UNDERSTAND HOW LUNAR EXOSPHERIC PICKUP IONS AND SURFACE WEATHERING ARE MODIFIED BY ELECTROSTATIC POTENTIALS. IN SUMMARY THE COMBINATION OF PLASMA DATA SETS OBTAINED BY ARTEMIS WITH SOLAR EUV DATA (SDO AND FISM) ENABLES DETERMINATION OF THE LUNAR SURFACE PHOTOEMISSIVITY FOR HIGH-ENERGY PHOTONS AND PROMOTES THE UNDERSTANDING OF THE LUNAR ELECTROSTATIC ENVIRONMENT.