Most people know that the winter solstice December 21 corresponds to the shortest day of the year in the northern hemisphere. But some go further and think that this date also corresponds to the time of latest sunrise and earliest sunset. That is not true. The earliest sunset occurs around December 8 and the latest sunrise around January 4.
The reason for this difference is that although sunset starts beginning to arrive later in the evening after December 8, sunrise is also getting later in the morning but at a faster rate, leading to decreasing overall day length. After the solstice, the rate at which sunset gets later outpaces the rate at which sunrise gets later, leading to increasing overall day length. After January 4, the days start getting longer at both ends, sunrise and sunset.
The coldest day of the year is on average around January 20, which is what I like to think of as mid-winter, rather than the solstice. So if we think of winter as the coldest quarter (91 days) of the year with the coldest day in the middle, then winter would be from December 6 to March 6. (See an earlier post for more details on temperature variation.)
This is why Groundhog Day on February 2 cracks me up. Supposedly, if Punxsutawney Phil does not see his shadow, spring will come early. But if he sees his shadow, then we will have to endure a long winter, in fact six more weeks of it. But six weeks from February 2 only takes us to March 16, hardly much longer than the regular end of winter on March 6.
But what I always look forward to is today, January 4. Knowing that the sun will now begin to rise earlier and earlier in the morning makes me feel that spring is around the corner. And after mid-winter on January 20, I feel that spring has pretty much arrived, whatever Phil might do two weeks later.