Private: Sun crosses celestial equator at March equinox
March 19, 2008 - ES Tonight, Uncategorized
Tomorrow – on Thursday, March 20 at precisely 5:48 a.m. “Universal Time”:http://earthsky.org/article/universal-time – the sun stands directly overhead at Earth’s equator.
This event – which happens during the night tonight for us in the United States – marks the March equinox, first day of spring or autumn depending on your location on Earth’s globe. The equinox comes on different dates from year to year. This one is early in part because 2008 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 equinox and all 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.
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.
I believe it is called “the first point of Ares”, not “the first point in Ares”.
Mark,
You are quite right. The zero point on the celestial sphere is generally called the First Point of Aries, though I noticed Eric Weisstein refers to this point as the First Point in Aries. Personally, I like to call the March equinox point the First Point of the sign Aries, so as to distinguish Aries the sign from Aries the constellation. According to Guy Ottewell’s 2008 Astronomical Calendar, the sun moves in front of the constellation Aries on Aril 18 (15 hours Universal Time) and into the sign of Taurus on April 19 (17 hours UT).
Bruce
Is it true when two blue moons occur in one year that all species will turn into supernatural beings?
Darin,
I’m afraid that you stumped me on that one! Did all the species turn into supernatural beings in 1999? In any event, I think blue moons are special and worthy of celebration!
Best wishes,
Bruce