This is the time of the year when we greet Old Man Winter and celebrate the solstice holidays, Christmas, Kwanzaa, and the Solstice itself.

If you live on Planet Earth the Winter Solstice’s significance is obvious. North of the equator, darkness comes too early. And the Sun rises late. In Philadelphia, PA this shortest day of the year is only nine hours long. If your latitude is higher than your day is even shorter. But if you live on the equator your hours of daylight and darkness remain the same all year ‘round.

Of course, this reverses if you live south of the equator.

This is the time of year when the Sun is at its most Southernly point in its apparent path around the Earth (the ecliptic). If you live along the latitude that is called the Tropic of Capricorn the Sun will be directly overhead at noon.

Although technically the Winter Solstice (and Capricorn’s entrance) came in at 5:23 pm on December 21st, the hours of daylight and darkness have been virtually unchanged for the preceding week and will remain so through Christmas.

That’s because the Sun’s speed around the ecliptic slows as it reaches its most northern and southern points.

Nonetheless, the shortest day of the year is not the same as the day of earliest sunset. In the northern hemisphere’s middle latitudes that occurs in early December. So it’s not your imagination that December nights are somehow darker.

Sunrise occurs later and later through the first week in January.

That’s because of the push-pull from the two phenomena occurring at the same time. First, due to its 23.5° tilt, the northern hemisphere faces away from the Sun. Its rays shine directly over the southern latitudes. Second, the Earth, whose orbit is elliptical—not perfectly round, is closest to the Sun at this time of year.

For northern hemisphere dwellers, these weeks are the darkest time of the year. But the dance of the Earth around the Sun is a constant. And as many civilizations have recognized through the ages, within the darkness is the promise of light’s return.

Because it always does.