Using 180¿ field of view (full-sky) imaging polarimetry, the patterns of the degree and angle of polarization of the moonlit clear night sky were measured in every half an hour throughout the night at full Moon. The patterns were compared with those of the sunlit sky. The observed patterns including the positions of the Arago and Babinet neutral points of the moonlit night sky and sunlit day sky are practically identical if the zenith angle of the Moon is the same as that of the sun. The possible biological relevance of the polarization pattern of the moonlit night sky in the polarization vision and orientation of night-active insects is briefly discussed. ¿ 2001 American Geophysical Union