In the North, which is where most of you readers are, it is the first day of Spring, the Vernal Equinox, today.  We are interested in this day in particular because we date Easter as the 1) first Sunday 2) after the first full Moon 3) on or after the Vernal Equinox.

An equinox (twice a year, in the Spring or in the Fall) is the exact moment when the plane of your planet’s equator passes through the geometric center of your yellow star’s disk.  The Sun’s “equator” is lined up with the Earth’s equator.

Aequinoctium in from aequus (equal) and nox (night).  At an equinox, daytime and nighttime are of approximately equal length.

In the Northern Hemisphere, the March equinox is called the vernal or spring equinox while the September equinox is called the autumnal or fall equinox. In the Southern Hemisphere, the reverse is true. The dates slightly vary due to leap years and other factors.

In the Roman Curia calendar, which I wrote about yesterday, I read that the Equinox occurred at 0937 UTC.

And the “Ave Maria” changed to 18:45!

In other news, in the far North watch for Aurora Borealis this weekend.  Check SpaceWeather.

About Fr. John Zuhlsdorf

Fr. Z is the guy who runs this blog. o{]:¬)
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  1. ps200306 says:

    I hope you’ll forgive this quibble but, astronomy being my passion, I felt compelled to point out a small inaccuracy. While the Earth’s equatorial plane does indeed cut the Sun’s geometric center on the equinox, it’s not true that “the Sun’s equator is lined up with the Earth’s equator”.

    The two bodies’ rotational axes have, to a very good approximation, fixed (and different) orientations in space. The Earth’s equatorial plane tilts at 23.5 degrees to the ecliptic plane (the plane of its orbit around the Sun). The Sun’s equator, on the other hand, tilts at around 7 degrees to the ecliptic. The two can never be aligned.

    Another way to think of this is to consider our respective “north stars”. For us, Polaris is the fixed reference point above our north pole that never moves in the sky. The sun’s “north star” would be in the constellation of Draco, close to ? Draconis. For us, that has a declination (i.e. “celestial latitude”) of 67 degrees — a long way from our own north star.

  2. Josephus Muris Saliensis says:

    Carissime ps200306,

    What a truly wonderful contribution. If I issued awards I would say this is the best blog comment for many years. Our poor world is in chaos, Holy Mother Church is in chaos, and you show us that eternal truths matter. I am not mocking, your contribution will bring countless thousands of Don Z’s readers to their senses. There is one Truth, containing two true things, God, and His Creation.

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