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diff --git a/ast/pal/palDh2e.c b/ast/pal/palDh2e.c
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+/*
+*+
+*  Name:
+*     palDh2e
+
+*  Purpose:
+*     Horizon to equatorial coordinates: Az,El to HA,Dec
+
+*  Language:
+*     Starlink ANSI C
+
+*  Type of Module:
+*     Library routine
+
+*  Invocation:
+*     palDh2e( double az, double el, double phi, double * ha, double * dec );
+
+*  Arguments:
+*     az = double (Given)
+*        Azimuth (radians)
+*     el = double (Given)
+*        Elevation (radians)
+*     phi = double (Given)
+*        Observatory latitude (radians)
+*     ha = double * (Returned)
+*        Hour angle (radians)
+*     dec = double * (Returned)
+*        Declination (radians)
+
+*  Description:
+*     Convert horizon to equatorial coordinates.
+
+*  Authors:
+*     PTW: Pat Wallace (STFC)
+*     TIMJ: Tim Jenness (JAC, Hawaii)
+*     {enter_new_authors_here}
+
+*  Notes:
+*     - All the arguments are angles in radians.
+*     - The sign convention for azimuth is north zero, east +pi/2.
+*     - HA is returned in the range +/-pi.  Declination is returned
+*       in the range +/-pi/2.
+*     - The latitude is (in principle) geodetic.  In critical
+*       applications, corrections for polar motion should be applied.
+*     - In some applications it will be important to specify the
+*       correct type of elevation in order to produce the required
+*       type of HA,Dec.  In particular, it may be important to
+*       distinguish between the elevation as affected by refraction,
+*       which will yield the "observed" HA,Dec, and the elevation
+*       in vacuo, which will yield the "topocentric" HA,Dec.  If the
+*       effects of diurnal aberration can be neglected, the
+*       topocentric HA,Dec may be used as an approximation to the
+*       "apparent" HA,Dec.
+*     - No range checking of arguments is done.
+*     - In applications which involve many such calculations, rather
+*       than calling the present routine it will be more efficient to
+*       use inline code, having previously computed fixed terms such
+*       as sine and cosine of latitude.
+
+*  History:
+*     2012-02-08 (TIMJ):
+*        Initial version with documentation taken from Fortran SLA
+*        Adapted with permission from the Fortran SLALIB library.
+*     {enter_further_changes_here}
+
+*  Copyright:
+*     Copyright (C) 1996 Rutherford Appleton Laboratory
+*     Copyright (C) 2012 Science and Technology Facilities Council.
+*     All Rights Reserved.
+
+*  Licence:
+*     This program is free software: you can redistribute it and/or
+*     modify it under the terms of the GNU Lesser General Public
+*     License as published by the Free Software Foundation, either
+*     version 3 of the License, or (at your option) any later
+*     version.
+*
+*     This program is distributed in the hope that it will be useful,
+*     but WITHOUT ANY WARRANTY; without even the implied warranty of
+*     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+*     GNU Lesser General Public License for more details.
+*
+*     You should have received a copy of the GNU Lesser General
+*     License along with this program.  If not, see
+*     <http://www.gnu.org/licenses/>.
+
+*  Bugs:
+*     {note_any_bugs_here}
+*-
+*/
+
+#include "pal.h"
+#include <math.h>
+
+void
+palDh2e ( double az, double el, double phi, double *ha, double *dec) {
+
+  double sa;
+  double ca;
+  double se;
+  double ce;
+  double sp;
+  double cp;
+
+  double x;
+  double y;
+  double z;
+  double r;
+
+  /*  Useful trig functions */
+  sa = sin(az);
+  ca = cos(az);
+  se = sin(el);
+  ce = cos(el);
+  sp = sin(phi);
+  cp = cos(phi);
+
+  /*  HA,Dec as x,y,z */
+  x = -ca * ce * sp + se * cp;
+  y = -sa * ce;
+  z = ca * ce * cp + se * sp;
+
+  /*  To HA,Dec */
+  r = sqrt(x * x + y * y);
+  if (r == 0.) {
+    *ha = 0.;
+  } else {
+    *ha = atan2(y, x);
+  }
+  *dec = atan2(z, r);
+
+  return;
+}