WINTER BEGINS today, December 21, 2021, at 10:59 AM EST. This is the precise moment that the Sun reaches its maximum southern declination. At this moment, the Sun “stands” and reverses its apparent southerly motion and begins to head north again, as seen from a geocentric perspective. Winter begins for the northern hemisphere, and the days begin to grow longer after this date.
From the heliocentric perspective, the Earth’s south pole is directly aligned with the Sun at the moment of solstice. Maximum sunlight prevails over the southern hemisphere while maximum annual darkness is the rule over the northern hemisphere. After that, the Earth’s orbital motion swings the south pole out of alignment and the northern hemisphere moves increasingly into the Sun’s rays.