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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Equinoxes: when Lon=0 (or 180) but not when Dec=0?
From: Bill B
Date: 2017 Aug 1, 15:53 -0400
From: Bill B
Date: 2017 Aug 1, 15:53 -0400
On 7/31/2017 9:08 AM, Tony Oz wrote: "Why the definition of Equinoxes demands the Sun's longitude to be equal to either 0° or 180°? The actual length of the day or night depends directly on the Sun's declination (rather than on its' longitude), so why not Dec == 0° then? Yes, I know that the orbital plane (of Earth) wobbles a bit (because of other planets' gravitation), but it is immediately translated into Sun's apparent declination, so I'm puzzled. Is it just for the simplicity of calculations (of the equinox of date)?" Perhaps the attached will help. Courtesy of Herbert Prinz, March 2006
File: 139659.equinox.doc
File:
