Tuesday, March 11, 2014
Every February, a strange claustrophobic restlessness sets in. Regarding the weather, I mean. It seems like we’ve been living in the darkness of the primordial chaos for eons.
The 8-foot snowbanks at the house end of the driveway are starting to seem like prison walls. Large, fluffy snowflakes that in December were a revelation of cosmic beauty now just throw Siberian shadows among the trees. The ten thousandth shovelful of snow weighs approximately what the same amount would weigh on Jupiter. Summer is apparently just a myth.
But every year around this time, something wonderful happens. Around 5:15 or so one afternoon in mid-month, you suddenly realize: Wait a minute, it’s not dark. You haven’t turned your car headlights on. You’re watching chickadees from the kitchen window at suppertime. You didn’t have to turn on a light this morning.
We all carry around a sort of transcendentalist’s faith in the reality of summer, so we know there’s more to the world than flickering afternoon shadow. But what’s startling to me is how the sun takes you by surprise. Daylight in late afternoon, a miracle of nature. And of course, careful cosmic arrangements are made for this awakening to occur.
You might remember this column explaining that the seasons arise because the Earth, as it orbits, is tilted on its axis with respect to the sun. That tilt always (for present purposes, anyway) points in the same direction, and so as the Earth circles, the North and South poles pass slowly in and out of the sun’s rays. In other words, from around March to around September, the North Pole is tilted toward the sun. The effect we see is the sun higher in the sky, giving us more daylight. Between September and March, the North Pole is tilted away from the sun, and the effect we see is the sun lower in the sky, giving us less daylight, and winter.
An interesting facet of this motion is that the sun does not get higher (from December to June) and lower (June to December) at an even rate. At the two solstices it seems to stall and not get much higher or lower, and at other times it kicks up and gets higher or lower faster day over day than at other times. The best example occurs in the dead of winter. At the winter solstice (Dec. 21 this year), the North Pole is facing away from the sun, and so for us the sun is at its lowest point in the midday sky. It barely clears the trees here in the Troy backyard. After that, the Northern Hemisphere starts edging back into the sun’s rays. The sun starts getting a little higher in the sky each day.
Around Jan. 1, the sun is gaining less than half a degree of altitude in the sky every five days. This is part of our problem in winter — months into the cold and snow, the sun doesn’t seem to be getting any brighter. This shadowy winterworld creeps on into January. Around the beginning of February, sunset is around 40 minutes later than it was a month earlier: The tilt of the Earth is taking us into night’s shadows at a pretty steady six or seven minutes later per five days.
But also, if you watch the sun around noon every day, you might notice in early February that it’s reaching a higher high point at a faster rate than it was in early January — a whole degree more gained per five days. In mid-February this heightening height kicks into a sort of mad cosmic gear. By the third week in February, the sun is climbing more than 1½ degrees higher in the sky every five days — more than triple the rate in early January. It’s around this time that the revelation of sunlight strikes.
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