SUBROUTINE sla_ECOR (RM, DM, IY, ID, FD, RV, TL) *+ * - - - - - * E C O R * - - - - - * * Component of Earth orbit velocity and heliocentric * light time in a given direction (single precision) * * Given: * RM,DM real mean RA, Dec of date (radians) * IY int year * ID int day in year (1 = Jan 1st) * FD real fraction of day * * Returned: * RV real component of Earth orbital velocity (km/sec) * TL real component of heliocentric light time (sec) * * Notes: * * 1 The date and time is TDB (loosely ET) in a Julian calendar * which has been aligned to the ordinary Gregorian * calendar for the interval 1900 March 1 to 2100 February 28. * The year and day can be obtained by calling sla_CALYD or * sla_CLYD. * * 2 Sign convention: * * The velocity component is +ve when the Earth is receding from * the given point on the sky. The light time component is +ve * when the Earth lies between the Sun and the given point on * the sky. * * 3 Accuracy: * * The velocity component is usually within 0.004 km/s of the * correct value and is never in error by more than 0.007 km/s. * The error in light time correction is about 0.03s at worst, * but is usually better than 0.01s. For applications requiring * higher accuracy, see the sla_EVP routine. * * Called: sla_EARTH, sla_CS2C, sla_VDV * * P.T.Wallace Starlink 24 November 1994 * * Copyright (C) 1995 Rutherford Appleton Laboratory *- IMPLICIT NONE REAL RM,DM INTEGER IY,ID REAL FD,RV,TL REAL sla_VDV REAL PV(6),V(3),AUKM,AUSEC * AU to km and light sec (1985 Almanac) PARAMETER (AUKM=1.4959787066E8, : AUSEC=499.0047837) * Sun:Earth position & velocity vector CALL sla_EARTH(IY,ID,FD,PV) * Star position vector CALL sla_CS2C(RM,DM,V) * Velocity component RV=-AUKM*sla_VDV(PV(4),V) * Light time component TL=AUSEC*sla_VDV(PV(1),V) END