NavList:

Hi Paul,

Similar values (about 1 second later) can be found in the monthly newsletter (lettre d’information) of the IMCCE (Institut de mécanique céleste et de calcul des éphémérides) at Paris

  https://www.imcce.fr/lettre-information/archives/160

If you want to receive future newsletters, you can sign up here

  https://www.imcce.fr/lettre-information/

Rob van Gent

From: NavList@fer3.com <NavList@fer3.com> On Behalf Of Paul Hirose
Sent: Fri 27 September 2019 18:46
To: Gent, R.H. van (Rob) <R.H.vanGent@uu.nl>
Subject: [NavList] Equinox, 2019 September

The four different "equinox" times (the third one is the formally

correct equinox):

07:49:53 Sun declination = 0

07:50:04 ITRS latitude = 0

07:50:11 ecliptic longitude = 0

07:50:14 right ascension = 12 h

Times are UTC on 2019-09-23.

computational basis:

JPL DE431 ephemeris

IAU 2006 precession

IAU 2000B nutation

0.2029 0.3185 polar motion x, y (arc sec)

If the Sun were exactly on the ecliptic, the first, third, and fourth

events would be simultaneous.

If not for polar motion, declination and ITRS latitude would be zero at

the same time. But Earth's axis of rotation (the celestial pole), which

is the basis of declination, is offset a few tenths of an arc second

from the geodetic (ITRS / WGS84) north pole.

The polar motion parameters I used are from IERS Bulletin A. The numbers

constantly change since the celestial pole follows a quasi circular path

with respect to the crust. One circle takes about 400 days and the

circle is about 20 feet in diameter. It is not centered on the geodetic

north pole, which is well outside the circle.