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    Re: Equinoxes: when Lon=0 (or 180) but not when Dec=0?
    From: Frank Reed
    Date: 2017 Aug 1, 14:53 -0700

    Tony Oz, you wrote:
    "Why the definition of Equinoxes demands the Sun's longitude to be equal to either 0° or 180°?"

    Well, probably nothing more complicated than deep history. The season definitions are really "astrological" in origin, from a modern perspective. The Sun enters the various "signs" at exact 30° increments of ecliptic longitude. Four out of those dozen sign-entry dates yield the equinoxes and solstices. Another way to look at it: a declination-based definition of the equinoxes would be relatively easy to implement, but this would be problematic for the solstices. The standard definition works equally well for all of these events.

    Frank Reed

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