I was listening to my local NPR on the drive home from work this afternoon when they had a short feature on Moscow. This past December Moscow saw only 6 minutes of sunlight. I'd never knew Moscow had such limited sun exposure in the Winter and the piece on NPR left me wondering, how much sunlight would there have been in December of 1941 as the Nazi's struggled through their doomed invasion of Moscow?
So just to clarify, I'm looking at a related New York Times article and it seems that the 6 minutes is describing the total amount of daylight in clear skies, versus the amount of time of total sunlight hours.
Meaning that it's a matter of the skies being overcast, versus being dark (unlike, say, in a polar winter above the Arctic Circle). The average day in Moscow in December lasts a little more than 7 hours.
Specifically around the winter of 1941-1942, it's worth noting that the weather was unusually cold (the coldest in the 20th century). Morning temperatures in Moscow were never above 0 C in December, and were usually around -30 C. When it's this cold, the weather is usually very clear and bright (it's too cold for overcast weather, clouds and snow), so I would imagine that most of December 1941 would have been exceptionally clear, bright and cold.
In contrast, December 2017 looks to have been overcast because the weather was unusually warm: the temperature rarely dipped below 0 C, and even went up as high as 8 C. This will create conditions that are cloudy and dark, even during daylight hours.
New York Times on December 2017 Moscow Daily
Daylight Calculator for Moscow
December 2017 Moscow Weather Conditions
The Severe Winter in Europe, 1941-1942, Bulletin of the American Meteorological Society, 1989 - http://journals.ametsoc.org/doi/pdf/10.1175/1520-0477(1989)070%3C0271:TSWIET%3E2.0.CO%3B2