src/Marando/IAU/iauSp00.php
public static function Sp00($date1, $date2) {
    $t;
    $sp;

    /* Interval between fundamental epoch J2000.0 and current date (JC). */
    $t = (($date1 - DJ00) + $date2) / DJC;

    /* Approximate s'. */
    $sp = -47e-6 * $t * DAS2R;

    return $sp;
  }
public static function Sp00($date1, $date2) {
    $t;
    $sp;

    /* Interval between fundamental epoch J2000.0 and current date (JC). */
    $t = (($date1 - DJ00) + $date2) / DJC;

    /* Approximate s'. */
    $sp = -47e-6 * $t * DAS2R;

    return $sp;
  }
public static function Sp00 ( $ date1 , $ date2 ) { $ t ; $ sp ; /* Interval between fundamental epoch J2000.0 and current date (JC). */ $ t = ( ( $ date1 - DJ00 ) + $ date2 ) / DJC ; /* Approximate s'. */ $ sp = - 47e-6 * $ t * DAS2R ; return $ sp ; }
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i a u S p 0 0
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The TIO locator s', positioning the Terrestrial Intermediate Origin
on the equator of the Celestial Intermediate Pole.

This function is part of the International Astronomical Union's
SOFA (Standards Of Fundamental Astronomy) software collection.

Status:  canonical model.

Given:
date1,date2  double    TT as a 2-part Julian Date (Note 1)

Returned (function value):
double    the TIO locator s' in radians (Note 2)

Notes:

1) The TT date date1+date2 is a Julian Date, apportioned in any
convenient way between the two arguments.  For example,
JD(TT)=2450123.7 could be expressed in any of these ways,
among others:

date1          date2

2450123.7           0.0       (JD method)
2451545.0       -1421.3       (J2000 method)
2400000.5       50123.2       (MJD method)
2450123.5           0.2       (date & time method)

The JD method is the most natural and convenient to use in
cases where the loss of several decimal digits of resolution
is acceptable.  The J2000 method is best matched to the way
the argument is handled internally and will deliver the
optimum resolution.  The MJD method and the date & time methods
are both good compromises between resolution and convenience.

2) The TIO locator s' is obtained from polar motion observations by
numerical integration, and so is in essence unpredictable.
However, it is dominated by a secular drift of about
47 microarcseconds per century, which is the approximation
evaluated by the present function.

Reference:

McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
IERS Technical Note No. 32, BKG (2004)

This revision:  2013 June 18

SOFA release 2015-02-09

Copyright (C) 2015 IAU SOFA Board.  See notes at end.
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