Sunset spots for equinoxes and solstices: montztermash

It’s equinox time. And this 2012 March equinox comes tomorrow – on Tuesday, March 20 at precisely 5:14 a.m. Universal Time. That’s the time in Greenwich, England, and it marks a single time for this equinox as noted from a whole-Earth perspective – when the sun stands directly overhead as seen from Earth’s equator.

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But, as always, our clocks will say different times. What this time means to us in the United States is that the equinox comes in the middle of the night – tonight, March 19. It’ll be only 10:14 p.m. tonight on the U.S. west coast – and 7:14 p.m. on March 19 in Hawaii. Meanwhile, it’ll be 1:14 a.m. Tuesday morning (March 20) according to clocks on the U.S. east coast. One event – different time zones and different times on the clock – when the sun crosses the celestial equator, bring this equinox to all of us around the globe.

Translating Universal Time to local time in U.S. time zones, that places the time of the equinox at 1:14 a.m. EDT (Tuesday, March 20), 12:14 a.m. CDT (Tuesday, March 20), 11:14 p.m. MDT (Monday, March 19) or 10:14 p.m. PDT (Monday, March 19).

How do I translate Universal Time into my time?

This event – which happens during the night tonight for us in the United States – marks the first day of spring or autumn, depending on your location north or south on Earth’s globe. The equinox comes at different times (and possibly different dates) from year to year. This one is early in part because 2012 is a leap year.

The March equinox happens when the sun crosses the celestial equator – an imaginary line around the sky above Earth’s equator moving south to north.

This intersection point is sometimes called the First Point in Aries. But at this March equinox and all of those in our lifetimes, it happens when the sun is in front of 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 was in front of Aries at the time of the equinox. Now the sun is in front of Pisces, and some 600 years in the future, the March equinox sun will shine in front of the constellation Aquarius. It’s a 26,000-year cycle – Earth’s precession – that causes our vantage point on the stars to shift.

The sun in front of the backdrop constellations on the Northern Hemisphere's spring equinox (Southern Hemisphere's autumn equinox).

Image credit: Wikimedia Commons

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 2012 vernal equinox – spring equinox for the Northern Hemisphere, and autumn equinox for the Southern Hemisphere – on Tuesday, March 20 at precisely 5:14 a.m. 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 the U.S. West and eastern Pacific, the equinox falls on the evening of March 19. The rest of the globe celebrates on March 20.