REAL FUNCTION sla_RVEROT (PHI, RA, DA, ST) *+ * - - - - - - - * R V E R O T * - - - - - - - * * Velocity component in a given direction due to Earth rotation * (single precision) * * Given: * PHI real latitude of observing station (geodetic) * RA,DA real apparent RA,DEC * ST real local apparent sidereal time * * PHI, RA, DEC and ST are all in radians. * * Result: * Component of Earth rotation in direction RA,DA (km/s) * * Sign convention: * The result is +ve when the observatory is receding from the * given point on the sky. * * Accuracy: * 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 * sla_PVOBS. * * P.T.Wallace Starlink 20 July 1994 * * Copyright (C) 1995 Rutherford Appleton Laboratory * * License: * 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 2 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 (see SLA_CONDITIONS); if not, write to the * Free Software Foundation, Inc., 59 Temple Place, Suite 330, * Boston, MA 02111-1307 USA * *- IMPLICIT NONE REAL PHI,RA,DA,ST * Nominal mean sidereal speed of Earth equator in km/s (the actual * value is about 0.4651) REAL ESPEED PARAMETER (ESPEED=0.4655) sla_RVEROT=ESPEED*COS(PHI)*SIN(ST-RA)*COS(DA) END