original_string: public static function Aper13($ut11, $ut12, iauASTROM &$astrom) {
      IAU::Aper(IAU::Era00($ut11, $ut12), $astrom);
  
      /* Finished. */
    }
code: public static function Aper13($ut11, $ut12, iauASTROM &$astrom) {
      IAU::Aper(IAU::Era00($ut11, $ut12), $astrom);
  
      /* Finished. */
    }
code_tokens: public static function Aper13 ( $ ut11 , $ ut12 , iauASTROM & $ astrom ) { IAU :: Aper ( IAU :: Era00 ( $ ut11 , $ ut12 ) , $ astrom ) ; /* Finished. */ }
docstring: - - - - - - - - - -
  i a u A p e r 1 3
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  In the star-independent astrometry parameters, update only the
  Earth rotation angle.  The caller provides UT1, (n.b. not UTC).
  
  This function is part of the International Astronomical Union's
  SOFA (Standards of Fundamental Astronomy) software collection.
  
  Status:  support function.
  
  Given:
  ut11    double      UT1 as a 2-part...
  ut12    double      ...Julian Date (Note 1)
  astrom  iauASTROM*  star-independent astrometry parameters:
  pmt    double       not used
  eb     double[3]    not used
  eh     double[3]    not used
  em     double       not used
  v      double[3]    not used
  bm1    double       not used
  bpn    double[3][3] not used
  along  double       longitude + s' (radians)
  xpl    double       not used
  ypl    double       not used
  sphi   double       not used
  cphi   double       not used
  diurab double       not used
  eral   double       not used
  refa   double       not used
  refb   double       not used
  
  Returned:
  astrom  iauASTROM*  star-independent astrometry parameters:
  pmt    double       unchanged
  eb     double[3]    unchanged
  eh     double[3]    unchanged
  em     double       unchanged
  v      double[3]    unchanged
  bm1    double       unchanged
  bpn    double[3][3] unchanged
  along  double       unchanged
  xpl    double       unchanged
  ypl    double       unchanged
  sphi   double       unchanged
  cphi   double       unchanged
  diurab double       unchanged
  eral   double       "local" Earth rotation angle (radians)
  refa   double       unchanged
  refb   double       unchanged
  
  Notes:
  
  1) The UT1 date (n.b. not UTC) ut11+ut12 is a Julian Date,
  apportioned in any convenient way between the arguments ut11 and
  ut12.  For example, JD(UT1)=2450123.7 could be expressed in any
  of these ways, among others:
  
  ut11           ut12
  
  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 and MJD methods are good compromises
  between resolution and convenience.  The date & time method is
  best matched to the algorithm used:  maximum precision is
  delivered when the ut11 argument is for 0hrs UT1 on the day in
  question and the ut12 argument lies in the range 0 to 1, or vice
  versa.
  
  2) If the caller wishes to provide the Earth rotation angle itself,
  the function iauAper can be used instead.  One use of this
  technique is to substitute Greenwich apparent sidereal time and
  thereby to support equinox based transformations directly.
  
  3) This is one of several functions that inserts into the astrom
  structure star-independent parameters needed for the chain of
  astrometric transformations ICRS <-> GCRS <-> CIRS <-> observed.
  
  The various functions support different classes of observer and
  portions of the transformation chain:
  
  functions         observer        transformation
  
  iauApcg iauApcg13    geocentric      ICRS <-> GCRS
  iauApci iauApci13    terrestrial     ICRS <-> CIRS
  iauApco iauApco13    terrestrial     ICRS <-> observed
  iauApcs iauApcs13    space           ICRS <-> GCRS
  iauAper iauAper13    terrestrial     update Earth rotation
  iauApio iauApio13    terrestrial     CIRS <-> observed
  
  Those with names ending in "13" use contemporary SOFA models to
  compute the various ephemerides.  The others accept ephemerides
  supplied by the caller.
  
  The transformation from ICRS to GCRS covers space motion,
  parallax, light deflection, and aberration.  From GCRS to CIRS
  comprises frame bias and precession-nutation.  From CIRS to
  observed takes account of Earth rotation, polar motion, diurnal
  aberration and parallax (unless subsumed into the ICRS <-> GCRS
  transformation), and atmospheric refraction.
  
  Called:
  iauAper      astrometry parameters: update ERA
  iauEra00     Earth rotation angle, IAU 2000
  
  This revision:   2013 September 25
  
  SOFA release 2015-02-09
  
  Copyright (C) 2015 IAU SOFA Board.  See notes at end.
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