From d54fe7c1f704a63824c5bfa0ece65245572e9b27 Mon Sep 17 00:00:00 2001 From: Joseph Hunkeler Date: Wed, 4 Mar 2015 21:21:30 -0500 Subject: Initial commit --- src/slalib/sun67.htx/node150.html | 202 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 202 insertions(+) create mode 100644 src/slalib/sun67.htx/node150.html (limited to 'src/slalib/sun67.htx/node150.html') diff --git a/src/slalib/sun67.htx/node150.html b/src/slalib/sun67.htx/node150.html new file mode 100644 index 0000000..4750c08 --- /dev/null +++ b/src/slalib/sun67.htx/node150.html @@ -0,0 +1,202 @@ + + + + +SLA_POLMO - Polar Motion + + + + + + + + + + + + +
+ +next + +up + +previous +
+ Next: SLA_PREBN - Precession Matrix (FK4) +
+Up: SUBPROGRAM SPECIFICATIONS +
+ Previous: SLA_PM - Proper Motion +

+

+

SLA_POLMO - Polar Motion +   +

+
+
ACTION: +
Polar motion: correct site longitude and latitude for polar +motion and calculate azimuth difference between celestial and + terrestrial poles. +

CALL: +
CALL sla_POLMO (ELONGM, PHIM, XP, YP, ELONG, PHI, DAZ) +

+

+
GIVEN: +
+
+ + + + + + + + + + + + + + + + + +
ELONGMDmean longitude of the site (radians, east +ve)
PHIMDmean geodetic latitude of the site (radians)
XPDpolar motion x-coordinate (radians)
YPDpolar motion y-coordinate (radians)
+

+
RETURNED: +
+
+ + + + + + + + + + + + + +
ELONGDtrue longitude of the site (radians, east +ve)
PHIDtrue geodetic latitude of the site (radians)
DAZDazimuth 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 sla_OBS 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 $0^{\circ}$, and YP is positive along the meridian at longitude + $270^\circ$ (i.e. $90^{\circ}$ west). Values for XP,YP can + be obtained from IERS circulars and equivalent publications; + the maximum amplitude observed so far is about + $0\hspace{-0.05em}^{'\hspace{-0.1em}'}\hspace{-0.4em}.3$ . +
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 sla_AOP and sla_AOPQK 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. +
+
+ +next + +up + +previous +
+ Next: SLA_PREBN - Precession Matrix (FK4) +
+Up: SUBPROGRAM SPECIFICATIONS +
+ Previous: SLA_PM - Proper Motion +

+

+

+SLALIB --- Positional Astronomy Library
Starlink User Note 67
P. T. Wallace
12 October 1999
E-mail:ptw@star.rl.ac.uk +
+ + -- cgit