Mist lifts over the Boyne Valley in Ireland as the Sun dawns on the stone tomb Newgrange. A narrow sunbeam streams through the passage just above the entrance. It reaches the floor and slowly crawls towards the back of an ancient crossed-shaped chamber. The beam of the rising Sun expands, flooding the tomb of ancestral ashes and bones with light for 17 minutes. This Stone-age alarm announces the 355th day of Earth’s year-long journey around the Sun. Today darkness yawns and stretches over the North, its longest stretch of the year.
In a wheat field nearby, Aisling glances up to see the Sun tracing its shortest arc. It hasn’t escaped her that the arc has been steadily dropping lower and becoming shorter since June. Today it has reached its nadir, a point so low that it almost looks like the Sun rises and sets in the same place. The Sun seems to “be standing still” or “sol sistere” in Latin. It’s the solstice, the year’s shortest day.
Even though she’s occupied with fixing her tractor and preparing it for the coming spring, Aisling can’t help feeling low. It seems as if her mood is hanging on that arc the Sun traces as it crosses the sky. And the lower the arc gets the lower her mood drops. Yet today she knows she should be cheerful because it marks the beginning of the Sun’s steady climb towards the long, warm days of summer. On that bright note, she strolls back home to enjoy the warmth of her fire while she roasts some chestnuts. Having been in the crisp winter air for so long, sitting near the fire almost burns her face. So she tilts back on the back legs of her chair to distance herself from the flames.
Somewhere tens of thousands of kilometres above Aisling’s head, a satellite snaps photos of our planet which tilts on its axis away from the Sun, arrogantly distancing its northern cheeks from the blazing ball of fire.
The axis is an imaginary line going right through Earth’s centre from “top” to “bottom” around which the planet spins. This axis doesn’t stand up straight, it leans over about 23 degrees. At the winter solstice it happens that the North Pole is leaning back just like Aisling on her chair. As Earth orbits the Sun throughout the year, this tilted axis always points in the same direction, so a different part of Earth would receive direct sunshine. If Aisling’s dad comes and turns her tilted chair ninety degrees to either side, the side of her body would all be equally exposed to the fire. At some point during its trip around the Sun, both Earth’s hemispheres will be equally illuminated, like Aisling’s side. This is the equinox, when daytime and night-time are almost equal. If Aisling’s dad then rotates her chair another ninety degrees, the back of her head would be leaning towards the fire. When the North Pole is leaning as such towards the Sun, the northern hemisphere gets direct sunlight and it is the summer solstice. It marks its longest day of the year, around the twenty-first of June.
So today because the North Pole is leaning back about 23 degrees, the Sun stays below its horizon and it’s cloaked in a day-long shadow. This is as far south as the Sun ever gets and the northern hemisphere is cooler, thus winter arrives. The Sun spreads more light over the southern globe which is leaning towards it and celebrating the opposite extreme, its summer solstice.
This reduced exposure of the northern hemisphere to the Sun’s rays makes its winter solstice the darkest day of the year, but not the coldest. In a month or so, the oceans and the land slowly start to lose the heat that they stored during the warmer months, and a cold spell falls over the Northern land.
The winter solstice was a special day to ancient civilisations who revered the Sun. The ancient tomb Newgrange was built so that today its rays can stream in and light up the chamber of the dead where the nobles have been lain to rest. In the Karnak Temple in the Egyptian city Luxor it rises between the temple’s pillars and shines down on its shrine. And when the shortest day is over, the Sun sets over robe-clad pagan worshippers celebrating the day at Stonehenge, and Iranians eating pomegranates and watermelons while chanting Hafez poems to drive away the long night. Aisling slowly peels her chestnuts as the hand of darkness stretches long and heavy over the frosty night.