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    Re: When is the Autumnal Equinox?
    From: Frank Reed
    Date: 2011 Sep 5, 13:47 -0700

    Paul, you wrote:
    "The equinoxes and solstices are the moments when the geocentric apparent
    Sun reaches 0, 90, 180, and 270 degrees of ecliptical longitude."

    Yes. Though carefully unstated by nearly all modern astronomers, these definitions are vestiges of the zodiac signs --which were a standard albeit archaic element of astronomy (not just astrology) well into the nineteenth century. When the geocentric apparent Sun enters the sign of Libra, which begins at 270 degrees ecliptic longitude, that instant marks the Autumnal Equinox. Note that Libra as a "sign" is no more and no less than the 30 degree band of ecliptic longitude from 270 up to 300. It does not correspond to the constellation. Note that there is an easy way to remember this: at the equinox, the day and night are equal so they balance on the scales of Libra. And it's possible that this "balance of night and day" is related to the origin of the constellation (which once matched the sign), but there is apparently conflicting historical evidence.

    By the way, by meteorological averages, for much of the northern hemisphere, fall begins right around September 7. The hottest day of the year averages July 21, the coldest averages January 21 (for mid-northern latitudes). So if you divide the year up into quarters placing the hottest and coldest days at the middle of summer and winter respectively, the meteorological seasons would end up starting about two weeks before the astronomical/astrological seasons. It's no coincidence that today, Labor Day in the US, marks the effective, civil end of summer. Right on schedule, it was actually chilly in Chicago last night.


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