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SUBROUTINE sla_RDPLAN (DATE, NP, ELONG, PHI, RA, DEC, DIAM)
*+
* - - - - - - -
* R D P L A N
* - - - - - - -
*
* Approximate topocentric apparent RA,Dec of a planet, and its
* angular diameter.
*
* Given:
* DATE d MJD of observation (JD - 2400000.5)
* NP i planet: 1 = Mercury
* 2 = Venus
* 3 = Moon
* 4 = Mars
* 5 = Jupiter
* 6 = Saturn
* 7 = Uranus
* 8 = Neptune
* 9 = Pluto
* else = Sun
* ELONG,PHI d observer's east longitude and geodetic
* latitude (radians)
*
* Returned:
* RA,DEC d RA, Dec (topocentric apparent, radians)
* DIAM d angular diameter (equatorial, radians)
*
* Notes:
*
* 1 The date is in a dynamical timescale (TDB, formerly ET) and is
* in the form of a Modified Julian Date (JD-2400000.5). For all
* practical purposes, TT can be used instead of TDB, and for many
* applications UT will do (except for the Moon).
*
* 2 The longitude and latitude allow correction for geocentric
* parallax. This is a major effect for the Moon, but in the
* context of the limited accuracy of the present routine its
* effect on planetary positions is small (negligible for the
* outer planets). Geocentric positions can be generated by
* appropriate use of the routines sla_DMOON and sla_PLANET.
*
* 3 The direction accuracy (arcsec, 1000-3000AD) is of order:
*
* Sun 5
* Mercury 2
* Venus 10
* Moon 30
* Mars 50
* Jupiter 90
* Saturn 90
* Uranus 90
* Neptune 10
* Pluto 1 (1885-2099AD only)
*
* The angular diameter accuracy is about 0.4% for the Moon,
* and 0.01% or better for the Sun and planets.
*
* See the sla_PLANET routine for references.
*
* Called: sla_GMST, sla_DT, sla_EPJ, sla_DMOON, sla_PVOBS, sla_PRENUT,
* sla_PLANET, sla_DMXV, sla_DCC2S, sla_DRANRM
*
* P.T.Wallace Starlink 26 May 1997
*
* Copyright (C) 1997 Rutherford Appleton Laboratory
*-
IMPLICIT NONE
DOUBLE PRECISION DATE
INTEGER NP
DOUBLE PRECISION ELONG,PHI,RA,DEC,DIAM
* AU in km
DOUBLE PRECISION AUKM
PARAMETER (AUKM=1.49597870D8)
* Light time for unit distance (sec)
DOUBLE PRECISION TAU
PARAMETER (TAU=499.004782D0)
INTEGER IP,J,I
DOUBLE PRECISION EQRAU(0:9),STL,VGM(6),V(6),RMAT(3,3),
: VSE(6),VSG(6),VSP(6),VGO(6),DX,DY,DZ,R,TL
DOUBLE PRECISION sla_GMST,sla_DT,sla_EPJ,sla_DRANRM
* Equatorial radii (km)
DATA EQRAU / 696000D0,2439.7D0,6051.9D0,1738D0,3397D0,71492D0,
: 60268D0,25559D0,24764D0,1151D0 /
* Classify NP
IP=NP
IF (IP.LT.0.OR.IP.GT.9) IP=0
* Approximate local ST
STL=sla_GMST(DATE-sla_DT(sla_EPJ(DATE))/86400D0)+ELONG
* Geocentre to Moon (mean of date)
CALL sla_DMOON(DATE,V)
* Nutation to true of date
CALL sla_NUT(DATE,RMAT)
CALL sla_DMXV(RMAT,V,VGM)
CALL sla_DMXV(RMAT,V(4),VGM(4))
* Moon?
IF (IP.EQ.3) THEN
* Yes: geocentre to Moon (true of date)
DO I=1,6
V(I)=VGM(I)
END DO
ELSE
* No: precession/nutation matrix, J2000 to date
CALL sla_PRENUT(2000D0,DATE,RMAT)
* Sun to Earth-Moon Barycentre (J2000)
CALL sla_PLANET(DATE,3,V,J)
* Precession and nutation to date
CALL sla_DMXV(RMAT,V,VSE)
CALL sla_DMXV(RMAT,V(4),VSE(4))
* Sun to geocentre (true of date)
DO I=1,6
VSG(I)=VSE(I)-0.012150581D0*VGM(I)
END DO
* Sun?
IF (IP.EQ.0) THEN
* Yes: geocentre to Sun
DO I=1,6
V(I)=-VSG(I)
END DO
ELSE
* No: Sun to Planet (J2000)
CALL sla_PLANET(DATE,IP,V,J)
* Precession and nutation to date
CALL sla_DMXV(RMAT,V,VSP)
CALL sla_DMXV(RMAT,V(4),VSP(4))
* Geocentre to planet
DO I=1,6
V(I)=VSP(I)-VSG(I)
END DO
END IF
END IF
* Refer to origin at the observer
CALL sla_PVOBS(PHI,0D0,STL,VGO)
DO I=1,6
V(I)=V(I)-VGO(I)
END DO
* Geometric distance (AU)
DX=V(1)
DY=V(2)
DZ=V(3)
R=SQRT(DX*DX+DY*DY+DZ*DZ)
* Light time (sec)
TL=TAU*R
* Correct position for planetary aberration
DO I=1,3
V(I)=V(I)-TL*V(I+3)
END DO
* To RA,Dec
CALL sla_DCC2S(V,RA,DEC)
RA=sla_DRANRM(RA)
* Angular diameter (radians)
DIAM=2D0*ASIN(EQRAU(IP)/(R*AUKM))
END
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