The vernal equinox, which occurs this year at 1:26 p.m. EST on March 20 and marks the official beginning of spring, has been a festive occasion from time immemorial. It heralds the seasonal period of renewal when the days become longer than the nights and when warmth and life return to the land. The early Egyptians marked the arrival of spring with a feast and built the Great Sphinx so that it points toward the rising sun on that day. For centuries, Christians have celebrated the resurrection rituals of Easter on the Sunday following the first full moon after the vernal equinox.
The astronomical cause of all this excitement is simple geometry: Earth's axis, which tilts at a 23.5 degree angle, points sideways relative to the sun on the equinox, so that the sun is positioned directly over the equator. With light and shadow cutting neatly across the globe, every ...
