Science of the Winter Solstice
How it ushers in the Winter Season
As I mentioned in my article on Advent, the Romans celebrated a holiday known as the Saturnalia, especially during the later Empire period, beginning with the Winter Solstice.
The word Solstice comes from the Latin “solstitium,” meaning “Sun, standing still.” This year it occurs in Greenwich, England (near London), at 3:27 am GMT (or UTC) on December 22, but in New York at 10:37 pm on December 21 and marks the first day of the Winter season in the Northern Hemisphere from an astronomical perspective.
Seasons
Earth enjoys different seasons because the planet is tilted 23 degrees and 27 minutes off the perpendicular to the plane of orbit. This means that the world revolves like a tilted spinning top. The Winter Solstice is the shortest day of sunlight as the Sun is at its lowest arc in the sky, at least in the Northern Hemisphere.
The farther north one is from the Equator, the more pronounced this is in Winter. However, as the Earth continues its orbit, the hemisphere that is angled closest to the sun changes, and the seasons are reversed.
Solstice: Standing Still
In the Northern Hemisphere, the sun appears at its lowest point in the sky, and its noontime elevation appears to be the same for several days before and after the solstice. In this way, it looks like the Sun is “standing still” from the perspective of someone standing on the Earth, until following the Winter Solstice, the days begin to grow longer and the nights shorter. In London, for example, on the Winter Solstice, the sun sets at 3:52 pm, and the “day” is only 7 hours and 50 mins long.
The Breathing Earth: A year of seasonal transformations on our planet, including the December solstice. John Nelson created this animation, using images from the NASA Visible Earth team.
Solstice and the Roman Saturnalia
I’ve written previously here and here about how the Romans celebrated Saturnalia around this time of year, honoring the head of their pantheon of Titans. Saturday gets its name from Saturn.
Know-it-all Facts to Impress Your Family and Friends
It is called the “shortest day of the year” or the “extreme of winter,” though it begins the Winter season. You cast your longest shadow at noon on this day. It has the fewest hours of sunlight and the most hours of darkness.
New York City: 9 hours, 15 minutes of sunlight
Helsinki, Finland: 5 hours, 49 minutes of sunlight
Barrow, Alaska: 0 minutes of sunlight — no sunrise at all, until January 22
Bill Petro, your friendly neighborhood historian
billpetro.com
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