Bill Jennings: Celebrate winter solstice by giving its due

The winter solstice occurred Thursday morning at 8.28 a.m. It’s a moment during the Earth’s 584 million mile journey around the sun often maligned for being the shortest day of the year. On the calendar, it’s the first day of winter. For skiers, riders and resort managers, the old man arrived just in the nick of time for the holidays.

He performed a great service by popping a stubborn bubble of high pressure that had trapped the ski season in a mediocre suspension. Early November storms got everyone excited for an epic Thanksgiving weekend. A pineapple express pulled the football away just when we were about to kick it.

This week the mountains finally put some real meat on the bone. This auspicious convergence of astronomical and meteorological winter couldn’t have had better timing. We should celebrate by giving the winter solstice its due.

Let’s consider this cosmic coincidence that has such a profound effect on our existence. We all learned in grade school that Earth spins on an axis tilted 23 degrees. Therefore, the northern hemisphere is always in the process of leaning into, or away from, the sun depending on Earth’s location in orbit.

At 8:28 Thursday morning we leaned furthest away. The sun was directly overhead at latitude 23.5 degrees south. Cities like Sao Paolo, Brazil will enjoy nearly 14 hours of sunlight today. We can expect only about 11 1/2. But as we ride on this massive ship moving at approximately 67,000 mph through space, the acute angle of the sun is already heading our way again.

The tilt of the planet’s spin gives us the impression that the sun swings from south to north and back again in the sky like a pendulum. Like the pendulum’s bob, the sun will appear briefly suspended in place for a few days at the end of its southernmost swing before accelerating back toward equilibrium – in this case, the spring equinox.

This pendulum-like swing of seasons is the likely reason why this date on the calendar is referred to as the “solstice.” The word’s Latin roots include sol (sun) and sistere (to stand still).

The Earth will also accelerate along its eccentric orbit as it travels away from the winter solstice. This is because right now the planet is at perihelion, its closest point to the sun. We are deep in our star’s gravity well. Our planet is about to receive a gravity assist much like the planetary boost given to spacecraft as they wend their way through the solar system.

If you pay attention, you will notice that the lengths of day and night will change very slowly at first. In fact, it will take until Saturday before the sun rises a minute sooner and sets a minute later.

But as we accelerate toward the equinox, the change in favor of light over dark will progress more rapidly. The greatest surge in daylight will occur around the first day of spring when skiing and riding conditions are peaking.

Like the bob of a pendulum swinging past equilibrium, the further away from the equinox we travel, the slower we will move. Earth will have decelerated back to its lowest orbital speed by the time we reach the summer solstice. There the planet is at aphelion, opposite of perihelion and furthest from the sun. At this point we begin to fall back into the sun’s gravity well. In the sky, the pendulum will begin to swing the other way as we accelerate toward another ski season.

Humans have been celebrating the promise of longer days to come for thousands of years. One of the best known, perhaps for its infamy, is the Saturnalia festival in ancient Rome. For seven days starting on Dec.17, ceasefires were declared, discipline and decorum were placed on hold and a carnival atmosphere prevailed. Revelry would inevitably devolve into debauched rioting in the streets.

That sort of public behavior is no longer tolerated in this more sober millennium. But you can celebrate the lengthening daylight, as well as the great skiing and riding promised by winter solstice 2017 a better way: on the snow.