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THE TILTED EARTH AT ITS “EQUAL NIGHT OF SPRING” (Excerpts)

New York Times, March 20, 2007

by Natalie Angier

…the vernal equinox is a momentous poem among moments, overspilling its borders like the swelling of sunlight it heralds. As with everything else about the seasons, the equinox is the result of Earth’s sizable tilt, 23.5 degrees relative to the plane of the orbit. That tilt is fairly fixed, and as Earth makes its way on its circumsolar migration and rotates on its imaginary skewer, the northern tip of the skewer always points toward the same spot in space, the bold sparkle of Polaris, the North Star.

Sometimes the northern skewer tip happens to be facing the Sun, and the northern hemisphere is bathed in the direct sunbeams and generous long days of summer, while the southern hemisphere receives only indirect lighting and hence calls the time winter. Six months later, the scene is reversed, with the northern axis tilted away from the Sun, and its hemisphere left to make do with the Sun’s cool, oblique glances.

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Twice a year the axial skewer tips are pointing neither toward nor away from the Sun, but instead are positioned exactly off to the side…These are the times of the equinox, when the linked geometry of Earth’s rotational and orbital planes together bestow a day of equal parts light and night across the entire globe. And while the equinox is formally calculated based on the moment when Earth first enters its profile position, the Sun is so comparatively huge that it takes us time to pass any point of it, and equinoctial conditions will effectively persist for several days.

Vernal equinox, the lovely little Latinate term that means “equal night of spring,” is used to indicate the March-based equinox even in the southern hemisphere, where the event is really the start of autumn…

The Great Sphinx of Egypt, built some 4,500 years ago, is positioned to face toward the rising sun on the vernal equinox.

In the 1,500-year-old Mayan city of Chichén Itzá, in Mexico’s Yucatán peninsula, the magnificent Kukulcán Pyramid practically slithers to life each spring equinox evening, as the waning sun casts a shadow along its steps of seven perfectly symmetrical isosceles triangles, a pattern suggesting the diamondback skin of a snake.

In the West, the equinox is intimately fastened to the holiest of Christian holidays: Easter is timed to occur the first Sunday after the first full moon that follows the vernal equinox.

Ecstatic, ecclesiastic, serpentine or Dionysian, the rebirth of the Earth offers a second chance to us all. Aren’t you glad you have two days to do it?

SOURCE: New York Times, 3/20/2007. Read the entire article at nytimes.com.

ILLUSTRATION: “Orange and olive” by Serge Bloch, ALL RIGHTS RESERVED.

ILLUSTRATION: “Vernal Equinox” by Ernestine Grindal. Prints available at fineartamerica.com.