ref: d67596f1bbdce63cd6a053cc17443fde1631ed10
dir: /sys/src/cmd/astro/merc.c/
#include "astro.h"
void
merc(void)
{
double pturbl, pturbr;
double lograd;
double dele, enom, vnom, nd, sl;
double q0, v0, t0, j0 , s0;
double lsun, elong, ci, dlong;
ecc = .20561421 + .00002046*capt - 0.03e-6*capt2;
incl = 7.0028806 + .0018608*capt - 18.3e-6*capt2;
node = 47.145944 + 1.185208*capt + .0001739*capt2;
argp = 75.899697 + 1.555490*capt + .0002947*capt2;
mrad = .3870986;
anom = 102.279381 + 4.0923344364*eday + 6.7e-6*capt2;
motion = 4.0923770233;
q0 = 102.28 + 4.092334429*eday;
v0 = 212.536 + 1.602126105*eday;
t0 = -1.45 + .985604737*eday;
j0 = 225.36 + .083086735*eday;
s0 = 175.68 + .033455441*eday;
q0 *= radian;
v0 *= radian;
t0 *= radian;
j0 *= radian;
s0 *= radian;
incl *= radian;
node *= radian;
argp *= radian;
anom = fmod(anom, 360.)*radian;
enom = anom + ecc*sin(anom);
do {
dele = (anom - enom + ecc * sin(enom)) /
(1. - ecc*cos(enom));
enom += dele;
} while(fabs(dele) > converge);
vnom = 2.*atan2(sqrt((1.+ecc)/(1.-ecc))*sin(enom/2.),
cos(enom/2.));
rad = mrad*(1. - ecc*cos(enom));
icosadd(mercfp, merccp);
pturbl = cosadd(2, q0, -v0);
pturbl += cosadd(2, q0, -t0);
pturbl += cosadd(2, q0, -j0);
pturbl += cosadd(2, q0, -s0);
pturbr = cosadd(2, q0, -v0);
pturbr += cosadd(2, q0, -t0);
pturbr += cosadd(2, q0, -j0);
/*
* reduce to the ecliptic
*/
lambda = vnom + argp + pturbl*radsec;
nd = lambda - node;
lambda = node + atan2(sin(nd)*cos(incl), cos(nd));
sl = sin(incl)*sin(nd);
beta = atan2(sl, pyth(sl));
lograd = pturbr*2.30258509;
rad *= 1. + lograd;
motion *= radian*mrad*mrad/(rad*rad);
semi = 3.34;
lsun = 99.696678 + 0.9856473354*eday;
lsun *= radian;
elong = lambda - lsun;
ci = (rad - cos(elong))/sqrt(1. + rad*rad - 2.*rad*cos(elong));
dlong = atan2(pyth(ci), ci)/radian;
mag = -.003 + .01815*dlong + .0001023*dlong*dlong;
helio();
geo();
}