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Re: Today’s the Spring Equinox
From: Paul Hirose
Date: 2019 Mar 25, 15:53 -0700
From: Paul Hirose
Date: 2019 Mar 25, 15:53 -0700
An eclipse has duration but an equinox does not, since it's the instant when the Sun geocentric apparent ecliptic longitude is 0 or 180. Declination, right ascension, and ITRS (geodetic) latitude pass through zero (or 12 hours) near every equinox, but none of those events is the true equinox. Nevertheless, zero geodetic latitude is a reasonable definition for a non-technical audience, since otherwise you have to explain ecliptic longitude. 2019 March 20 21:57:47 UTC zero dec 21:57:58 UTC zero ITRS lat 21:58:26 UTC * zero ecliptic lon 21:58:33 UTC zero RA * correct time of equinox JPL DE431 ephemeris, IAU 2006 precession, and 2000B nutation. Polar motion x = 0.0438", y = 0.3704". I did the computation a month or two before the equinox and so the polar motion parameters are a little different from the final values determined by the IERS. Unfortunately, the IMCCE was not equally clear about the basis of their super precise determination that the equinox occurred at 21:58:27.05 UTC. I have not been able to duplicate that.
