Winter (December) Solstice in the Northern hemisphere occurs the day of this event, December 21, 2024 at about 1:20 am or about 7 hours ahead of the event. What is the Winter Solstice? It is the moment when, due to the declination of the Earth's axis relative to the Solar Orbit, the sun is above its southern most point on earth for the entire year (Tropic of Capricorn) and therefore occurs in the 24-hour period with the least sunlight of the year in the northern hemisphere. The Summer Solstice in the Northern hemisphere is the moment when the sun is above the northern most point on earth for the entire year (Tropic of Cancer) and both of the Equinoxes occur at the moment when the sun is directly above the equator. The length of sunlight per day is shortest just before and just after the Winter Solstice and then the change in length of sunlight per day increases daily up to the Spring (or Vernal) Equinox afterwhich the change in length of sunlight per day decreaes daily up to the Summer Solstice then the reverse occurs over the next six months.
If there were exactly 365 days in every calendar year without any leap years needed, then the Solstices and Equinoxes would occur at exactly the same time of day each and every year. But that is not the case. One revolution of the earth around the sun takes slightly less than 365 1/4 days. If one revolution took exactly 365 1/4 days, then leap year would occur every four years, on and on forever. However, since one revolution take slightly less then there needs to be fewer leap years overall. So to account for this unevenness in time for one revolution, leap years are omitted every hundred years at the turn of a century but one more adjustment is needed because a revolution takes slightly less than 365 1/4 years and this is achieved by maintaining leap years at every fourth turn of a century. So in 1600 there was a leap year but in 1700, 1800 and 1900, leap years are omitted then in 2000, leap year was maintained (remember, it was only 24+ years ago!). Then leap year will be omitted again in 2100 (put that on your calendar), 2200 and 2300 then maintained in 2400. And so on. So Solstices and Equinoxes move forward a little less than six hours each year for three years then back up a little less than 18 hours and this four year sequence continues on and on.
Reminder: You can qualify for the December Solstice souvenir by attending this event!