Natural Night Sky Brightness during Solar Minimum

In 2018, Solar Cycle 24 entered into a solar minimum phase. During this period, 11 million zenithal night sky brightness (NSB) data were collected at different dark sites around the planet, including astronomical observatories and natural protected areas, with identical broadband Telescope Encoder Sky Sensor photometers (based on Unihedron Quality Meter TLS237 sensor). A detailed observational review of multiple effects that contribute to NSB measurement has been conducted optimal filters designed avoid brightening by Sun, Moon, clouds, other sources (the Galaxy zodiacal light). The calculated from percentiles for 44 applying these new filters. pristine was measured change an amplitude 0.1 mag/arcsec2 in all photometers, which is suggested be due variations scales up months compatible semiannual oscillations. We report systematic observation short-time vast majority nights find related airglow events forming above mesosphere.