SLA_EQEQX

Equation of the Equinoxes

ACTION:

Equation of the equinoxes (IAU 1994).

CALL:

D = sla_EQEQX (DATE)

GIVEN:

RETURNED:

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 $\Delta \psi cosϵ$ 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.