According to the astronomical calendar, winter begins around December 21st. For meteorologists and climatologists, winter has already begun on December 1st, and the season lasts exactly three calendar months.
Solstice: the time or date (twice each year) at which the sun reaches its maximum or minimum declination, marked by the longest and shortest days (about 21 June and 21or22 December)
This logic, who comes up with this crap? Some temperature measurement?
365days per year/4seasons/2=46
46days before 21december = 5 November winter starts
46days after 21december = 5 February winter ends