From fa080de7afc95aa1c19a6e6fc0e0708ced2eadc4 Mon Sep 17 00:00:00 2001
From: Joseph Hunkeler <jhunkeler@gmail.com>
Date: Wed, 8 Jul 2015 20:46:52 -0400
Subject: Initial commit

---
 math/slalib/doc/polmo.hlp | 87 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 87 insertions(+)
 create mode 100644 math/slalib/doc/polmo.hlp

(limited to 'math/slalib/doc/polmo.hlp')

diff --git a/math/slalib/doc/polmo.hlp b/math/slalib/doc/polmo.hlp
new file mode 100644
index 00000000..b3f68383
--- /dev/null
+++ b/math/slalib/doc/polmo.hlp
@@ -0,0 +1,87 @@
+.help polmo Jun99 "Slalib Package"
+.nf
+
+      SUBROUTINE slPLMO ( ELONGM, PHIM, XP, YP, ELONG, PHI, DAZ )
+
+     - - - - - -
+      P L M O
+     - - - - - -
+
+  Polar motion:  correct site longitude and latitude for polar
+  motion and calculate azimuth difference between celestial and
+  terrestrial poles.
+
+  Given:
+     ELONGM   d      mean longitude of the observer (radians, east +ve)
+     PHIM     d      mean geodetic latitude of the observer (radians)
+     XP       d      polar motion x-coordinate (radians)
+     YP       d      polar motion y-coordinate (radians)
+
+  Returned:
+     ELONG    d      true longitude of the observer (radians, east +ve)
+     PHI      d      true geodetic latitude of the observer (radians)
+     DAZ      d      azimuth correction (terrestrial-celestial, radians)
+
+  Notes:
+
+   1)  "Mean" longitude and latitude are the (fixed) values for the
+       site's location with respect to the IERS terrestrial reference
+       frame;  the latitude is geodetic.  TAKE CARE WITH THE LONGITUDE
+       SIGN CONVENTION.  The longitudes used by the present routine
+       are east-positive, in accordance with geographical convention
+       (and right-handed).  In particular, note that the longitudes
+       returned by the slOBS routine are west-positive, following
+       astronomical usage, and must be reversed in sign before use in
+       the present routine.
+
+   2)  XP and YP are the (changing) coordinates of the Celestial
+       Ephemeris Pole with respect to the IERS Reference Pole.
+       XP is positive along the meridian at longitude 0 degrees,
+       and YP is positive along the meridian at longitude
+       270 degrees (i.e. 90 degrees west).  Values for XP,YP can
+       be obtained from IERS circulars and equivalent publications;
+       the maximum amplitude observed so far is about 0.3 arcseconds.
+
+   3)  "True" longitude and latitude are the (moving) values for
+       the site's location with respect to the celestial ephemeris
+       pole and the meridian which corresponds to the Greenwich
+       apparent sidereal time.  The true longitude and latitude
+       link the terrestrial coordinates with the standard celestial
+       models (for precession, nutation, sidereal time etc).
+
+   4)  The azimuths produced by slAOP and slAOPQ are with
+       respect to due north as defined by the Celestial Ephemeris
+       Pole, and can therefore be called "celestial azimuths".
+       However, a telescope fixed to the Earth measures azimuth
+       essentially with respect to due north as defined by the
+       IERS Reference Pole, and can therefore be called "terrestrial
+       azimuth".  Uncorrected, this would manifest itself as a
+       changing "azimuth zero-point error".  The value DAZ is the
+       correction to be added to a celestial azimuth to produce
+       a terrestrial azimuth.
+
+   5)  The present routine is rigorous.  For most practical
+       purposes, the following simplified formulae provide an
+       adequate approximation:
+
+       ELONG = ELONGM+XP*COS(ELONGM)-YP*SIN(ELONGM)
+       PHI   = PHIM+(XP*SIN(ELONGM)+YP*COS(ELONGM))*TAN(PHIM)
+       DAZ   = -SQRT(XP*XP+YP*YP)*COS(ELONGM-ATAN2(XP,YP))/COS(PHIM)
+
+       An alternative formulation for DAZ is:
+
+       X = COS(ELONGM)*COS(PHIM)
+       Y = SIN(ELONGM)*COS(PHIM)
+       DAZ = ATAN2(-X*YP-Y*XP,X*X+Y*Y)
+
+   Reference:  Seidelmann, P.K. (ed), 1992.  "Explanatory Supplement
+               to the Astronomical Almanac", ISBN 0-935702-68-7,
+               sections 3.27, 4.25, 4.52.
+
+  P.T.Wallace   Starlink   22 February 1996
+
+  Copyright (C) 1995 Rutherford Appleton Laboratory
+  Copyright (C) 1995 Association of Universities for Research in Astronomy Inc.
+
+.fi
+.endhelp
-- 
cgit 

