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`prec76, `

`jdtdb1`, `jdtdb2`, `zeta`, `z`,
`theta`

[SOFA] Returns the three Euler angles

(1st rotation,
radians clockwise around z), `zeta`

(3rd rotation, radians
clockwise around z), `z`

(2nd rotation, radians
counterclockwise around y) which implement general precession between
epochs (TDB Julian Dates) `theta`

and `jdtdb1`

,
using the IAU 1976 model (as for the FK5 catalog).
`jdtdb2`

The precession matrix is `r_3(-z) r_2(+theta) r_3(-zeta)`

.

The absolute accuracy is better than 0.1 arcsec from year 1960 through 2040, better than 1 arcsec from 1640 through 2360, and remains below 3 arcsec during -500 through 3000. The errors exceed 10 arcsec outside -1200 through 3900, exceed 100 arcsec outside -4200 through 5600, and exceed 1000 arcsec outside -6800 through 8200.

See also: Astronomical Coordinate Calculations