1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91

/*
*+
* Name:
* palRverot
* Purpose:
* Velocity component in a given direction due to Earth rotation
* Language:
* Starlink ANSI C
* Type of Module:
* Library routine
* Invocation:
* double palRverot ( double phi, double ra, double da, double st );
* Arguments:
* phi = double (Given)
* latitude of observing station (geodetic) (radians)
* ra = double (Given)
* apparent RA (radians)
* da = double (Given)
* apparent Dec (radians)
* st = double (Given)
* Local apparent sidereal time.
* Returned Value:
* palRverot = double
* Component of Earth rotation in direction RA,DA (km/s).
* The result is +ve when the observatory is receding from the
* given point on the sky.
* Description:
* Calculate the velocity component in a given direction due to Earth
* rotation.
*
* The simple algorithm used assumes a spherical Earth, of
* a radius chosen to give results accurate to about 0.0005 km/s
* for observing stations at typical latitudes and heights. For
* applications requiring greater precision, use the routine
* palPvobs.
* Authors:
* PTW: Patrick T. Wallace
* TIMJ: Tim Jenness (JAC, Hawaii)
* {enter_new_authors_here}
* History:
* 20120302 (TIMJ):
* Initial version
* Adapted with permission from the Fortran SLALIB library.
* {enter_further_changes_here}
* Copyright:
* Copyright (C) 1995 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 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
* MA 021101301, USA.
* Bugs:
* {note_any_bugs_here}
*
*/
#include "pal.h"
#include <math.h>
double palRverot ( double phi, double ra, double da, double st ) {
/* Nominal mean sidereal speed of Earth equator in km/s (the actual
* value is about 0.4651) */
const double espeed = 0.4655;
return espeed * cos(phi) * sin(stra) * cos(da);
}
