ref: d67596f1bbdce63cd6a053cc17443fde1631ed10
dir: /sys/src/cmd/astro/star.c/
#include "astro.h"
void
star(void)
{
double xm, ym, zm, dxm, dym, dzm;
double xx, yx, zx, yy, zy, zz, tau;
double capt0, capt1, capt12, capt13, sl, sb, cl;
/*
* remove E-terms of aberration
* except when finding catalog mean places
*/
alpha += (.341/(3600.*15.))*sin((alpha+11.26)*15.*radian)
/cos(delta*radian);
delta += (.341/3600.)*cos((alpha+11.26)*15.*radian)
*sin(delta*radian) - (.029/3600.)*cos(delta*radian);
/*
* correct for proper motion
*/
tau = (eday - epoch)/365.24220;
alpha += tau*da/3600.;
delta += tau*dd/3600.;
alpha *= 15.*radian;
delta *= radian;
/*
* convert to rectangular coordinates merely for convenience
*/
xm = cos(delta)*cos(alpha);
ym = cos(delta)*sin(alpha);
zm = sin(delta);
/*
* convert mean places at epoch of startable to current
* epoch (i.e. compute relevant precession)
*/
capt0 = (epoch - 18262.427)/36524.220e0;
capt1 = (eday - epoch)/36524.220;
capt12 = capt1*capt1;
capt13 = capt12*capt1;
xx = - (.00029696+26.e-8*capt0)*capt12
- 13.e-8*capt13;
yx = -(.02234941+1355.e-8*capt0)*capt1
- 676.e-8*capt12 + 221.e-8*capt13;
zx = -(.00971690-414.e-8*capt0)*capt1
+ 207.e-8*capt12 + 96.e-8*capt13;
yy = - (.00024975+30.e-8*capt0)*capt12
- 15.e-8*capt13;
zy = -(.00010858+2.e-8*capt0)*capt12;
zz = - (.00004721-4.e-8*capt0)*capt12;
dxm = xx*xm + yx*ym + zx*zm;
dym = - yx*xm + yy*ym + zy*zm;
dzm = - zx*xm + zy*ym + zz*zm;
xm = xm + dxm;
ym = ym + dym;
zm = zm + dzm;
/*
* convert to mean ecliptic system of date
*/
alpha = atan2(ym, xm);
delta = atan2(zm, sqrt(xm*xm+ym*ym));
cl = cos(delta)*cos(alpha);
sl = cos(delta)*sin(alpha)*cos(obliq) + sin(delta)*sin(obliq);
sb = -cos(delta)*sin(alpha)*sin(obliq) + sin(delta)*cos(obliq);
lambda = atan2(sl, cl);
beta = atan2(sb, sqrt(cl*cl+sl*sl));
rad = 1.e9;
if(px != 0)
rad = 20600/px;
motion = 0;
semi = 0;
helio();
geo();
}