$LastChangedDate: 27-Juil-2011 $

# CL_mod_equinoxesEquation

Equation of the equinoxes (IERS 1996)

## Calling Sequence

       [equi[,equip]]=CL_mod_equinoxesEquation(dPsi,eps0,F5[,dPsip,eps0p,F5p])

## Description

- Computes equation of the equinoxes: Greenwich sideral time - Mean Greenwich sideral time (standard IERS 1996)

## Parameters

dPsi:

  longitude (see CL_mod_nutationAngles) [rad](1xN)

dPsip:

  (optional with eps0p and F5p) longitude first time derivative (see CL_mod_nutationAngles) [rad/s] (1xN)

eps0:

  mean obliquity (see CL_mod_meanObliquity) [rad] (1xN)

eps0p:

  (optional with dPsip and F5p) mean obliquity first time derivative (see CL_mod_meanObliquity) [rad/s] (1xN)

F5:

  Mean longitude of Moon's ascending node (see CL_mod_nutationArg) [rad] (1xN)

F5p:

  (optional with eps0p and dPsip) Mean longitude of Moon's ascending node first time derivative (see CL_mod_nutationArg) [rad/s] (1xN)

equi:

  equinoxes equation (1xN)

equip:

  (optional, needs dPsip, eps0p and F5p) first time derivative of equi (1xN)

## Authors

- CNES - DCT/SB

## Bibliography

- 1) IERS Conventions (1996), Dennis D. McCarthy

- 2) Explanatory Supplement to the Astronomical Almanac, Seidelman (1992)

## See also

- CL_mod_nutationAngles

- CL_mod_nutationArg

- CL_mod_meanObliquity

## Examples

    jj_tai = [19500:1:20500];
    ss_tai = 43200*ones(jj_tai);
    // Nutation angles (dPsi,dEps) :
    [NUT,F,NUTP,FP,NUTPP,FPP]=CL_mod_nutationAngles(jj_tai,ss_tai,"s");

    // Mean obliquity :
    [eps0,eps0p,eps0pp]=CL_mod_meanObliquity(jj_tai,ss_tai,"s");

    // Equinoxes equation :
    [equi,equip]=CL_mod_equinoxesEquation(NUT(1,:),eps0,F(5,:),NUTP(1,:),eps0p,FP(5,:));
    plot(jj_tai'+ss_tai'/86400,equi');