# Lunar sky brightness

Looking at the report "The Measurements of Sky Brightness on Lunokhod-2"1, I read that the day time visible light sky brightness was so large that it was off the scale. Unfortunately I have no idea how to convert their units of measurement into units I am familiar with, lux or lumens.

Reference

1. Severny, A. & Terez, Edward & Zvereva, A.. (1975). The measurements of sky brightness on Lunokhod-2. Earth Moon and Planets - EARTH MOON PLANET. 14. 123-128. 10.1007/BF00562978. (pdf)
Well, for ultraviolet light they give (table I), $$4.68-25.8 ~\text{ergs/s}\times 10^5$$, which would correspond to $$80-260 ~\text{mW}$$. As about a visual light, seems Lunokhod-2 telemetry systems was measuring sky brigntness in S10 units,- relative light intensity to some "standard candle",- light captured from a main sequence star per 1 square degree solid angle. In these units Earth typical night sky has about $$220~S_{10}$$ brightness. Lunokhod-2 claims giving brightness readings, even when within a shadow, of $$4400~S_{10}$$ units. That's about $$20\times$$ bigger brightness than at Earth night sky ! It may seem far too big value for a moon, but considering that moon has no light pollution, no atmosphere which would scatter Sun/stars light, and on average gray color of surface (which reflects light not bad, especially if you are in the highland calcium-rich region, which is brighter),- then it almost makes sense.