### SLA_EQEQX

Equation of the Equinoxes

ACTION:
Equation of the equinoxes (IAU 1994).
CALL:
D = sla_EQEQX (DATE)
##### GIVEN:
 DATE D TDB (formerly ET) as Modified Julian Date (JD$-$2400000.5)

##### RETURNED:
 sla_EQEQX D The equation of the equinoxes (radians)

NOTES:
(1)
The equation of the equinoxes is defined here as GAST $-$ GMST: it is added to a mean sidereal time to give the apparent sidereal time.
(2)
The change from the classic “textbook” expression $\Delta \psi \phantom{\rule{0.3em}{0ex}}cos\phantom{\rule{0.3em}{0ex}}ϵ$ occurred with IAU Resolution C7, Recommendation 3 (1994). The new formulation takes into account cross-terms between the various precession and nutation quantities, amounting to about 3 milliarcsec. The transition from the old to the new model officially took place on 1997 February 27.
REFERENCE:
Capitaine, N. & Gontier, A.-M. (1993), Astron. Astrophys., 275, 645-650.