The sidereal period is slightly longer than 27 days and the synodic period is slightly longer than 29 days. The variable lunar surface temperatures are a function of solar illumination and shadows. The roughly 300 degree temperature differences can be experienced at the same time on a piece of equipment depending on its orientation with respect to solar illumination and deep space. The radiation environment of the moon is harsh. Crewmembers are not protected from these ionizing particles by either an atmosphere or a magnetosphere.
Solar protons pose a significant risk to inadequately shielded crewmembers.
Very large energetic particle events, which can cause acute radiation effects, occur at intervals of 7 to 10 years. Intermediate events, which can limit mission activities, occur several times each year. For nominal flares, build-up to peak radiation intensity occurs within a few hours or less. Monitoring of X-ray precursors may provide 30 minutes to one hour of additional warning. We must contend with life threatening radiation hazards on the lunar surface.