You probably know the winter solstice marks the time the Sun reaches its most southerly point in its apparent path around the Sun marking the beginning of astronomical (and astrological) winter. And if, on that day, you were standing at the Tropic of Capricorn, 23.5° south of the equator, and looked up at noon, the Sun would be directly overhead. Meanwhile back in the northern hemisphere, nights are longest and the Sun lowest in the sky.
And then a funny thing happens. The Sun appears to come to a dead stop. For three days. Hence the name Solstice (Sol = Sun sistere = stop).1 It’s not really stopped–it’s just moving V-E-R-Y slowly. The Sun is pivoting and beginning its northward trek. But this won’t become apparent until December 25th when it V-E-R-Y slowly begins to pick up speed. And the speed accelerates until it reaches its maximum at the vernal equinox. Which is why the hours of daylight and darkness seem to change so quickly in the spring and fall.
What you may not know is despite the fact that the hours of darkness are at their maximum, the winter solstice is not the day of the earliest sunset. In fact,
“the Sun has already begun to set later. The date of earliest sunset is dependent on your latitude. In Philadelphia, for example, 40° North, earliest sunset occurs on December 7th.2 The reason has to do with the discrepancy between the actual daily motion of the Sun (measured from noon to noon) versus mechanical clock which averages out all variation.
When Earth and Sun are closest in December and January, the Sun appears to move eastward a bit faster, covering more sky each day compared to the other seasons. This creates a delay in sunrise time, making for later sunrises. A later sunrise also means the Sun arrives at the sunset point later. Let’s use this fact to explore the disconnect between the solstice and earliest sunsets.
In late November and early December, the Sun is sinking to its southernmost point in the sky, so its daytime arc is getting shorter and shorter, lower and lower. This southward slide pairs up with the Sun’s flight east, delaying sunrise even more.
At the solstice, the Sun begins moving north again. Its arc steepens and days begin to get longer. But that extra eastward movement still keeps it rising later for a time until the effect is canceled out by the Sun’s steady and steepening northward creep up the ecliptic. Result? Sunrises start coming earlier. This happens in early January from the mid-northern latitudes, when the Sun begins to both set and rise later.”3
Once the solstice has occurred, sunrise continues to occur later but the hours between sunrise and sunset slowly begin to lengthen. At 40° North, there are 28.5 days between earliest sunset (December 7th) and latest sunrise (January 5th).4
Then there is the phenomenon called seasonal lag that explains why the shortest days of the year are not the coldest days of the year.
“It happens because the amount of solar energy arriving at the ground is less than the amount leaving the earth for a few more weeks (a bit like a bank account that starts losing money when you make more withdrawals than deposits). Oceans and bodies of water — which take longer than land to heat up and cool down — keep temperatures from rising very fast. Not until the Northern Hemisphere sees a net gain in solar energy (more heat coming in than going out) do average temperatures begin their ascent.”5
Although the winter season has just begun, the winter solstice promises the return of warmth and light. Just hang in there.