public static function Aper13($ut11, $ut12, iauASTROM &$astrom) {
    IAU::Aper(IAU::Era00($ut11, $ut12), $astrom);

    /* Finished. */
  }
public static function Aper13($ut11, $ut12, iauASTROM &$astrom) {
    IAU::Aper(IAU::Era00($ut11, $ut12), $astrom);

    /* Finished. */
  }
public static function Aper13 ( $ ut11 , $ ut12 , iauASTROM & $ astrom ) { IAU :: Aper ( IAU :: Era00 ( $ ut11 , $ ut12 ) , $ astrom ) ; /* Finished. */ }
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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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