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the constellation Pisces. Over the long course of time, different constellations provide a backdrop to the sun as it soars above the Earth's equator, going from south to north, year after year.
• Over 2,000 years ago, the March equinox sun shone in front of the constellation Aries. Now the sun is in front of Pisces on the March equinox, and 600 years in the future, the March equinox sun will shine in the constellation Aquarius. It's a 26,000-year cycle - Earth's precession - that causes our vantage point on the stars to shift.
• By the way, according to the mathematical wizard Jean Meeus, the March equinox sun passed out of the constellation Aries and into the constellation Pisces in 68 B.C. Not until A.D. 2597 will the March equinox sun leave the constellation Pisces and enter into the constellation Aquarius.
• Of course, the date on which the sun crosses a constellation boundary depends entirely on the location of that boundary. And the drawing of constellation boundaries is a human pursuit. The International Astronomical Union officially decided on the current boundaries of the constellations early in the 20th century.
• So, wherever you are on Earth's globe, celebrate this equinox, as the sun crosses the celestial equator, going from south to north!
• Bottom line: The 2013 vernal equinox - spring equinox for the Northern Hemisphere, and autumn equinox for the Southern Hemisphere - on Wednesday, March 20 at precisely 11:02 Universal Time. That's the time from a whole-Earth perspective - when the sun stands directly overhead as seen from Earth's equator. Meanwhile, our clocks say different times. For most of the U.S., the equinox takes place before sunrise on March 20.
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