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XEphem/libastro/jupmoon.c

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/* jupiter moon info */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <math.h>
#include "astro.h"
#include "bdl.h"
static int use_bdl (double jd, char *dir, MoonData md[J_NMOONS]);
static void meeus_jupiter (double d, double *cmlI, double *cmlII,
MoonData md[J_NMOONS]);
static void moonradec (double jupsize, MoonData md[J_NMOONS]);
static void moonSVis (Obj *sop, Obj *jop, MoonData md[J_NMOONS]);
static void moonEVis (MoonData md[J_NMOONS]);
static void moonPShad (Obj *sop, Obj *jop, MoonData md[J_NMOONS]);
static void moonTrans (MoonData md[J_NMOONS]);
/* moon table and a few other goodies and when it was last computed */
static double mdmjd = -123456;
static MoonData jmd[J_NMOONS] = {
{"Jupiter", NULL},
{"Io", "I"},
{"Europa", "II"},
{"Ganymede", "III"},
{"Callisto", "IV"}
};
static double sizemjd; /* size at last mjd */
static double cmlImjd; /* central meridian long sys I, at last mjd */
static double cmlIImjd; /* " II " */
/* These values are from the Explanatory Supplement.
* Precession degrades them gradually over time.
*/
#define POLE_RA degrad(268.05) /* RA of Jupiter's north pole */
#define POLE_DEC degrad(64.50) /* Dec of Jupiter's north pole */
/* get jupiter info in md[0], moon info in md[1..J_NMOONS-1].
* if !dir always use meeus model.
* if !jop caller just wants md[] for names
* N.B. we assume sop and jop are updated.
*/
void
jupiter_data (
double Mjd, /* mjd */
char dir[], /* dir in which to look for helper files */
Obj *sop, /* Sun */
Obj *jop, /* jupiter */
double *sizep, /* jup angular diam, rads */
double *cmlI, double *cmlII, /* central meridian longitude, rads */
double *polera, double *poledec, /* pole location */
MoonData md[J_NMOONS]) /* return info */
{
double JD;
/* always copy back at least for name */
memcpy (md, jmd, sizeof(jmd));
/* pole */
if (polera) *polera = POLE_RA;
if (poledec) *poledec = POLE_DEC;
/* nothing else if repeat call or just want names */
if (Mjd == mdmjd || !jop) {
if (jop) {
*sizep = sizemjd;
*cmlI = cmlImjd;
*cmlII = cmlIImjd;
}
return;
}
JD = Mjd + MJD0;
/* planet in [0] */
md[0].ra = jop->s_ra;
md[0].dec = jop->s_dec;
md[0].mag = get_mag(jop);
md[0].x = 0;
md[0].y = 0;
md[0].z = 0;
md[0].evis = 1;
md[0].svis = 1;
/* size is straight from jop */
*sizep = degrad(jop->s_size/3600.0);
/* mags from JPL ephemeris */
md[1].mag = 5.7;
md[2].mag = 5.8;
md[3].mag = 5.3;
md[4].mag = 6.7;
/* get moon data from BDL if possible, else Meeus' model.
* always use Meeus for cml
*/
if (dir && use_bdl (JD, dir, md) == 0)
meeus_jupiter (Mjd, cmlI, cmlII, NULL);
else
meeus_jupiter (Mjd, cmlI, cmlII, md);
/* set visibilities */
moonSVis (sop, jop, md);
moonPShad (sop, jop, md);
moonEVis (md);
moonTrans (md);
/* fill in moon ra and dec */
moonradec (*sizep, md);
/* save */
mdmjd = Mjd;
sizemjd = *sizep;
cmlImjd = *cmlI;
cmlIImjd = *cmlII;
memcpy (jmd, md, sizeof(jmd));
}
/* hunt for BDL file in dir[] and use if possible
* return 0 if ok, else -1
*/
static int
use_bdl (
double JD, /* julian date */
char dir[], /* directory */
MoonData md[J_NMOONS]) /* fill md[1..NM-1].x/y/z for each moon */
{
#define JUPRAU .0004769108 /* jupiter radius, AU */
double x[J_NMOONS], y[J_NMOONS], z[J_NMOONS];
char buf[1024];
FILE *fp;
char *fn;
int i;
/* check ranges and appropriate data file */
if (JD < 2451179.50000) /* Jan 1 1999 UTC */
return (-1);
if (JD < 2455562.5) /* Jan 1 2011 UTC */
fn = "jupiter.9910";
else if (JD < 2459215.5) /* Jan 1 2021 UTC */
fn = "jupiter.1020";
else if (JD < 2466520.5) /* Jan 1 2041 UTC */
fn = "jupiter.2040";
else
return (-1);
/* open */
(void) sprintf (buf, "%s/%s", dir, fn);
fp = fopen (buf, "r");
if (!fp) {
fprintf (stderr, "%s: %s\n", fn, strerror(errno));
return (-1);
}
/* use it */
if ((i = read_bdl (fp, JD, x, y, z, buf)) < 0) {
fprintf (stderr, "%s: %s\n", fn, buf);
fclose (fp);
return (-1);
}
if (i != J_NMOONS-1) {
fprintf (stderr, "%s: BDL says %d moons, code expects %d", fn,
i, J_NMOONS-1);
fclose (fp);
return (-1);
}
/* copy into md[1..NM-1] with our scale and sign conventions */
for (i = 1; i < J_NMOONS; i++) {
md[i].x = x[i-1]/JUPRAU; /* we want jup radii +E */
md[i].y = -y[i-1]/JUPRAU; /* we want jup radii +S */
md[i].z = -z[i-1]/JUPRAU; /* we want jup radii +front */
}
/* ok */
fclose (fp);
return (0);
}
/* compute location of GRS and Galilean moons.
* if md == NULL, just to cml.
* from "Astronomical Formulae for Calculators", 2nd ed, by Jean Meeus,
* Willmann-Bell, Richmond, Va., U.S.A. (c) 1982, chapters 35 and 36.
*/
static void
meeus_jupiter(
double d,
double *cmlI, double *cmlII, /* central meridian longitude, rads */
MoonData md[J_NMOONS]) /* fill in md[1..NM-1].x/y/z for each moon.
* N.B. md[0].ra/dec must already be set
*/
{
#define dsin(x) sin(degrad(x))
#define dcos(x) cos(degrad(x))
double A, B, Del, J, K, M, N, R, V;
double cor_u1, cor_u2, cor_u3, cor_u4;
double solc, tmp, G, H, psi, r, r1, r2, r3, r4;
double u1, u2, u3, u4;
double lam, Ds;
double z1, z2, z3, z4;
double De, dsinDe;
double theta, phi;
double tvc, pvc;
double salpha, calpha;
int i;
V = 134.63 + 0.00111587 * d;
M = (358.47583 + 0.98560003*d);
N = (225.32833 + 0.0830853*d) + 0.33 * dsin (V);
J = 221.647 + 0.9025179*d - 0.33 * dsin(V);
A = 1.916*dsin(M) + 0.02*dsin(2*M);
B = 5.552*dsin(N) + 0.167*dsin(2*N);
K = (J+A-B);
R = 1.00014 - 0.01672 * dcos(M) - 0.00014 * dcos(2*M);
r = 5.20867 - 0.25192 * dcos(N) - 0.00610 * dcos(2*N);
Del = sqrt (R*R + r*r - 2*R*r*dcos(K));
psi = raddeg (asin (R/Del*dsin(K)));
*cmlI = degrad(268.28 + 877.8169088*(d - Del/173) + psi - B);
range (cmlI, 2*PI);
*cmlII = degrad(290.28 + 870.1869088*(d - Del/173) + psi - B);
range (cmlII, 2*PI);
/* that's it if don't want moon info too */
if (!md)
return;
solc = (d - Del/173.); /* speed of light correction */
tmp = psi - B;
u1 = 84.5506 + 203.4058630 * solc + tmp;
u2 = 41.5015 + 101.2916323 * solc + tmp;
u3 = 109.9770 + 50.2345169 * solc + tmp;
u4 = 176.3586 + 21.4879802 * solc + tmp;
G = 187.3 + 50.310674 * solc;
H = 311.1 + 21.569229 * solc;
cor_u1 = 0.472 * dsin (2*(u1-u2));
cor_u2 = 1.073 * dsin (2*(u2-u3));
cor_u3 = 0.174 * dsin (G);
cor_u4 = 0.845 * dsin (H);
r1 = 5.9061 - 0.0244 * dcos (2*(u1-u2));
r2 = 9.3972 - 0.0889 * dcos (2*(u2-u3));
r3 = 14.9894 - 0.0227 * dcos (G);
r4 = 26.3649 - 0.1944 * dcos (H);
md[1].x = -r1 * dsin (u1+cor_u1);
md[2].x = -r2 * dsin (u2+cor_u2);
md[3].x = -r3 * dsin (u3+cor_u3);
md[4].x = -r4 * dsin (u4+cor_u4);
lam = 238.05 + 0.083091*d + 0.33*dsin(V) + B;
Ds = 3.07*dsin(lam + 44.5);
De = Ds - 2.15*dsin(psi)*dcos(lam+24.)
- 1.31*(r-Del)/Del*dsin(lam-99.4);
dsinDe = dsin(De);
z1 = r1 * dcos(u1+cor_u1);
z2 = r2 * dcos(u2+cor_u2);
z3 = r3 * dcos(u3+cor_u3);
z4 = r4 * dcos(u4+cor_u4);
md[1].y = z1*dsinDe;
md[2].y = z2*dsinDe;
md[3].y = z3*dsinDe;
md[4].y = z4*dsinDe;
/* compute sky transformation angle as triple vector product */
tvc = PI/2.0 - md[0].dec;
pvc = md[0].ra;
theta = PI/2.0 - POLE_DEC;
phi = POLE_RA;
salpha = -sin(tvc)*sin(theta)*(cos(pvc)*sin(phi) - sin(pvc)*cos(phi));
calpha = sqrt (1.0 - salpha*salpha);
for (i = 0; i < J_NMOONS; i++) {
double tx = md[i].x*calpha + md[i].y*salpha;
double ty = -md[i].x*salpha + md[i].y*calpha;
md[i].x = tx;
md[i].y = ty;
}
md[1].z = z1;
md[2].z = z2;
md[3].z = z3;
md[4].z = z4;
}
/* given jupiter loc in md[0].ra/dec and size, and location of each moon in
* md[1..NM-1].x/y in jup radii, find ra/dec of each moon in md[1..NM-1].ra/dec.
*/
static void
moonradec (
double jupsize, /* jup diameter, rads */
MoonData md[J_NMOONS]) /* fill in RA and Dec */
{
double juprad = jupsize/2;
double jupra = md[0].ra;
double jupdec = md[0].dec;
int i;
for (i = 1; i < J_NMOONS; i++) {
double dra = juprad * md[i].x;
double ddec = juprad * md[i].y;
md[i].ra = jupra + dra;
md[i].dec = jupdec - ddec;
}
}
/* set svis according to whether moon is in sun light */
static void
moonSVis(
Obj *sop, /* SUN */
Obj *jop, /* jupiter */
MoonData md[J_NMOONS])
{
double esd = sop->s_edist;
double eod = jop->s_edist;
double sod = jop->s_sdist;
double soa = degrad(jop->s_elong);
double esa = asin(esd*sin(soa)/sod);
double h = sod*jop->s_hlat;
double nod = h*(1./eod - 1./sod);
double sca = cos(esa), ssa = sin(esa);
int i;
for (i = 1; i < J_NMOONS; i++) {
MoonData *mdp = &md[i];
double xp = sca*mdp->x + ssa*mdp->z;
double yp = mdp->y;
double zp = -ssa*mdp->x + sca*mdp->z;
double ca = cos(nod), sa = sin(nod);
double xpp = xp;
double ypp = ca*yp - sa*zp;
double zpp = sa*yp + ca*zp;
int outside = xpp*xpp + ypp*ypp > 1.0;
int infront = zpp > 0.0;
mdp->svis = outside || infront;
}
}
/* set evis according to whether moon is geometrically visible from earth */
static void
moonEVis (MoonData md[J_NMOONS])
{
int i;
for (i = 1; i < J_NMOONS; i++) {
MoonData *mdp = &md[i];
int outside = mdp->x*mdp->x + mdp->y*mdp->y > 1.0;
int infront = mdp->z > 0.0;
mdp->evis = outside || infront;
}
}
/* set pshad and sx,sy shadow info */
static void
moonPShad(
Obj *sop, /* SUN */
Obj *jop, /* jupiter */
MoonData md[J_NMOONS])
{
int i;
for (i = 1; i < J_NMOONS; i++) {
MoonData *mdp = &md[i];
mdp->pshad = !plshadow (jop, sop, POLE_RA, POLE_DEC, mdp->x,
mdp->y, mdp->z, &mdp->sx, &mdp->sy);
}
}
/* set whether moons are transiting */
static void
moonTrans (MoonData md[J_NMOONS])
{
int i;
for (i = 1; i < J_NMOONS; i++) {
MoonData *mdp = &md[i];
mdp->trans = mdp->z > 0 && mdp->x*mdp->x + mdp->y*mdp->y < 1;
}
}
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