void
sunpos(double jd, int apparent, double *ra, double *dec, double *rv, double* slong)
{
double t, t2, t3, l, m, e, ea, v, theta, omega, eps;
// Time, in Julian centuries of 36525 ephemeris days,
// measured from the epoch 1900 January 0.5 ET.
t = (jd - 2415020.0) / 36525.0;
t2 = t * t;
t3 = t2 * t;
// Geometric mean longitude of the Sun, referred to the
// mean equinox of the date.
l = fixangle(279.69668 + 36000.76892 * t + 0.0003025 * t2);
// Sun's mean anomaly.
m = fixangle(358.47583 + 35999.04975*t - 0.000150*t2 - 0.0000033*t3);
// Eccentricity of the Earth's orbit.
e = 0.01675104 - 0.0000418 * t - 0.000000126 * t2;
// Eccentric anomaly.
ea = kepler(m, e);
// True anomaly
v = fixangle(2 * rtd(atan(sqrt((1 + e) / (1 - e)) * tan(ea / 2))));
// Sun's true longitude.
theta = l + v - m;
// Obliquity of the ecliptic.
eps = 23.452294 - 0.0130125 * t - 0.00000164 * t2 + 0.000000503 * t3;
// Corrections for Sun's apparent longitude, if desired.
if (apparent) {
omega = fixangle(259.18 - 1934.142 * t);
theta = theta - 0.00569 - 0.00479 * sin(dtr(omega));
eps += 0.00256 * cos(dtr(omega));
}
// Return Sun's longitude and radius vector
*slong = theta;
*rv = (1.0000002 * (1 - e * e)) / (1 + e * cos(dtr(v)));
// Determine solar co-ordinates.
*ra = fixangle(rtd(atan2(cos(dtr(eps)) * sin(dtr(theta)), cos(dtr(theta)))));
*dec = rtd(asin(sin(dtr(eps)) * sin(dtr(theta))));
}
EXPORT double sun_ecliptic_longitude (double jday)
{ /* Calculate ecliptic longitude of the sun */
double T, O, M, L;
T = (jday - 2451545.0) / 36525.0;
O = deg2rad(282.9400);
M = deg2rad(357.5256 + 35999.049 * T);
L = O + M + (6191.2 * T + 6893.0 * sin(M) + 72.0 * sin(2.0 * M))
/ 1296000.0 * 2.0 * M_PI;
return fixangle(rad2deg(L));
}
static double
phase( double pdate,
double *pphase, /* Illuminated fraction */
double *mage, /* Age of moon in days */
double *dist, /* Distance in kilometres */
double *angdia, /* Angular diameter in degrees */
double *sudist, /* Distance to Sun */
double *suangdia ) /* Sun's angular diameter */
{
double Day, N, M, Ec, Lambdasun, ml, MM, MN, Ev, Ae, A3, MmP,
mEc, A4, lP, V, lPP, NP, y, x, Lambdamoon,
MoonAge, MoonPhase,
MoonDist, MoonDFrac, MoonAng,
F, SunDist, SunAng;
/* Calculation of the Sun's position */
Day = pdate - epoch; /* Date within epoch */
N = fixangle((360.0 / 365.2422) * Day); /* Mean anomaly of the Sun */
M = fixangle(N + elonge - elongp); /* Convert from perigee
co-ordinates to epoch 1980.0 */
Ec = kepler(M, eccent); /* Solve equation of Kepler */
Ec = sqrt((1.0 + eccent) / (1.0 - eccent)) * tan(Ec / 2.0);
Ec = 2.0 * todeg(atan(Ec)); /* True anomaly */
Lambdasun = fixangle(Ec + elongp); /* Sun's geocentric ecliptic
longitude */
/* Orbital distance factor */
F = ((1.0 + eccent * cos(torad(Ec))) / (1.0 - eccent * eccent));
SunDist = sunsmax / F; /* Distance to Sun in km */
SunAng = F * sunangsiz; /* Sun's angular size in degrees */
/* Calculation of the Moon's position */
/* Moon's mean longitude */
ml = fixangle(13.1763966 * Day + mmlong);
/* Moon's mean anomaly */
MM = fixangle(ml - 0.1114041 * Day - mmlongp);
/* Moon's ascending node mean longitude */
MN = fixangle(mlnode - 0.0529539 * Day);
/* Evection */
Ev = 1.2739 * sin(torad(2.0 * (ml - Lambdasun) - MM));
/* Annual equation */
Ae = 0.1858 * sin(torad(M));
/* Correction term */
A3 = 0.37 * sin(torad(M));
/* Corrected anomaly */
MmP = MM + Ev - Ae - A3;
/* Correction for the equation of the centre */
mEc = 6.2886 * sin(torad(MmP));
/* Another correction term */
A4 = 0.214 * sin(torad(2.0 * MmP));
/* Corrected longitude */
lP = ml + Ev + mEc - Ae + A4;
/* Variation */
V = 0.6583 * sin(torad(2.0 * (lP - Lambdasun)));
/* True longitude */
lPP = lP + V;
/* Corrected longitude of the node */
NP = MN - 0.16 * sin(torad(M));
/* Y inclination coordinate */
y = sin(torad(lPP - NP)) * cos(torad(minc));
/* X inclination coordinate */
x = cos(torad(lPP - NP));
/* Ecliptic longitude */
Lambdamoon = todeg(atan2(y, x));
Lambdamoon += NP;
#if 0
/* Ecliptic latitude */
(void)todeg(asin(sin(torad(lPP - NP)) * sin(torad(minc))));
#endif
/* Calculation of the phase of the Moon */
/* Age of the Moon in degrees */
MoonAge = lPP - Lambdasun;
/* Phase of the Moon */
MoonPhase = (1.0 - cos(torad(MoonAge))) / 2.0;
/* Calculate distance of moon from the centre of the Earth */
MoonDist = (msmax * (1.0 - mecc * mecc)) /
(1.0 + mecc * cos(torad(MmP + mEc)));
/* Calculate Moon's angular diameter */
MoonDFrac = MoonDist / msmax;
MoonAng = mangsiz / MoonDFrac;
#if 0
/* Calculate Moon's parallax */
MoonPar = mparallax / MoonDFrac;
#endif
*pphase = MoonPhase;
*mage = synmonth * (fixangle(MoonAge) / 360.0);
*dist = MoonDist;
*angdia = MoonAng;
*sudist = SunDist;
*suangdia = SunAng;
return fixangle(MoonAge) / 360.0;
}
