‘Tis the season for the pious and pagans alike to celebrate the light of the world in metaphor and in fact. The December 21 winter solstice marks the day when the tilting axis of the earth offers the full underbelly of the southern hemisphere to the sun, giving all of us here in the north the dark, cold shoulder of the season. We crave light – any light. So we put lights on trees. We put lights in our houses. We put trees in our houses and then put lights on them. Still, the margins of the day draw tightly around our working hours so unless you are some kind of slacker who is late to work and early to head home, dawn and dusk are your commuting companions.
The silver lining in all this December astronomical gloom is… well, a red lining. More people get to watch sunrises in December than at any other time of year. It requires no extreme early rising. On December 21, the sun will rise at 7:16 am. Many of us are already on the road by then, or at least sitting at the kitchen table looking out the window. The new day starts with a rosy glow at the horizon, overhung with the banners and buntings of clouds pinking up against the brightening sky. And there are moments in the most spectacular sunrises when the unseen hand of physics fiddles with the hue and saturation dials so that the whole sky ignites in reds and oranges and then quickly fades like burning tissue paper tossed on the fire.
The colors of a sunrise appear and then disappear quickly with the changing angle of the sun. The white light of the sun contains all the colors of the visible light spectrum, but the earth’s atmospheric cloak scatters light as a prism does. The atmosphere’s world-worn condition has infused it with dust, aerosols, and other earthly particles that absorb, reflect, and otherwise interfere with the transmission of shorter wavelength light at the green-to-blue end of the spectrum but have little effect on the long-wavelength reds and oranges in sunlight. When the sun sits on the horizon at sunrise, its light traverses a thicker slice of atmosphere, increasing the scattering of blues and violets, giving the horizon the bloodshot aspect of a night watchman at dawn. As the sun ascends, the angle of the atmosphere/prism shifts, and the reds and oranges fade. The scattered blue of the sky regroups to seize the day.
Of course, if you want to prolong the fleeting beauty of a sunrise, you can move to either of the earth’s poles. In his classic polar adventure autobiography, Alone, Admiral Richard E. Byrd describes this Antarctic sunrise: The sun rose this morning at about 9:30 o’clock, but never really left the horizon. Huge and red and solemn it rolled like a wheel along the Barrier edge for about two and a half hours when the sunrise met the sunset at noon. For another two and a half hours, it rolled along the horizon, gradually sinking past it until nothing was left but a blood-red incandescence.
Fortunately, the sun isn’t quite that stingy with its light at our latitude, and our cravings for illumination are amply met by the bright traditions of this season. But for all the candles in the windows and all the lights on the trees, our mood would be dark indeed without these December mornings, when each day sleeps late and awakens with a blush.