On March 20, as on every vernal equinox, schoolchildren learn and the media proclaim that day and night are equal everywhere. It’s an appealing thought. Our planet, flying through space in a Charlie Chaplin wobble, momentarily, at 4:29 P.M. eastern time, tilts neither toward nor away from the sun. In theory this balancing act bestows a universal equilibrium. And in fact it is a time of approximate equality in most of the world, a far howl from the long nights and short days we’ve endured the past several months. But the truth is both more complex and more interesting than the common wisdom.
The monkey wrench thrown into this worldwide equality business is our own atmosphere. Whenever a celestial body sits on the skyline, the horizon’s thick air bends its image upward by half a degree, the way a glass of water appears to bend a spoon. By sheer coincidence, ...
