/* CalcEphem.c
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330,
* Boston, MA 02111-1307, USA.
*
* Original (C) Mike Henderson <mghenderson@lanl.gov>.
*
* I've converted to glib types, removed unused variables and functions,
* piped the whole thing through indent, and added small stuff.
*
* (C) 1999-2004 Josh Buhl <jbuhl@users.sourceforge.net>
*
*/
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif
#include "CalcEphem.h"
#include "Moon.h"
static gdouble
kepler(gdouble M, gdouble e)
{
gint n = 0;
gdouble E, Eold, eps = 1.0e-8;
E = M + e * sin(M);
do {
Eold = E;
E = Eold + (M - Eold + e * sin(Eold))
/ (1.0 - e * cos(Eold));
++n;
} while ((fabs(E - Eold) > eps) && (n < 100));
return (E);
}
static gint
DayofYear(gint year, gint month, gint day)
{
gdouble jd();
return ((gint) (jd(year, month, day, 0.0) - jd(year, 1, 0, 0.0)));
}
static gint
DayofWeek(gint year, gint month, gint day, gchar dowstr[])
{
gdouble JD, A, Afrac, jd();
gint n, iA;
JD = jd(year, month, day, 0.0);
A = (JD + 1.5) / 7.0;
iA = (gint) A;
Afrac = A - (gdouble) iA;
n = (gint) (Afrac * 7.0 + 0.5);
switch (n) {
case 0:
strcpy(dowstr, "Sunday");
break;
case 1:
strcpy(dowstr, "Monday");
break;
case 2:
strcpy(dowstr, "Tuesday");
break;
case 3:
strcpy(dowstr, "Wednesday");
break;
case 4:
strcpy(dowstr, "Thursday");
break;
case 5:
strcpy(dowstr, "Friday");
break;
case 6:
strcpy(dowstr, "Saturday");
break;
}
return (n);
}
/*
* Compute the Julian Day number for the given date.
* Julian Date is the number of days since noon of Jan 1 4713 B.C.
*/
gdouble
jd(gint ny, gint nm, gint nd, gdouble UT)
{
gdouble A, B, C, D, JD, day;
day = nd + UT / 24.0;
if ((nm == 1) || (nm == 2)) {
ny = ny - 1;
nm = nm + 12;
}
if (((gdouble) ny + nm / 12.0 + day / 365.25) >=
(1582.0 + 10.0 / 12.0 + 15.0 / 365.25)) {
A = ((gint) (ny / 100.0));
B = 2.0 - A + (gint) (A / 4.0);
} else {
B = 0.0;
}
if (ny < 0.0) {
C = (gint) ((365.25 * (gdouble) ny) - 0.75);
} else {
C = (gint) (365.25 * (gdouble) ny);
}
D = (gint) (30.6001 * (gdouble) (nm + 1));
JD = B + C + D + day + 1720994.5;
return (JD);
}
gdouble
hour24(gdouble hour)
{
gint n;
if (hour < 0.0) {
n = (gint) (hour / 24.0) - 1;
return (hour - n * 24.0);
} else if (hour > 24.0) {
n = (gint) (hour / 24.0);
return (hour - n * 24.0);
} else {
return (hour);
}
}
gdouble
angle2pi(gdouble angle)
{
gint n;
gdouble a;
a = 2.0 * M_PI;
if (angle < 0.0) {
n = (gint) (angle / a) - 1;
return (angle - n * a);
} else if (angle > a) {
n = (gint) (angle / a);
return (angle - n * a);
} else {
return (angle);
}
}
static gdouble
angle360(gdouble angle)
{
gint n;
if (angle < 0.0) {
n = (gint) (angle / 360.0) - 1;
return (angle - n * 360.0);
} else if (angle > 360.0) {
n = (gint) (angle / 360.0);
return (angle - n * 360.0);
} else {
return (angle);
}
}
void
CalcEphem(glong date, gdouble UT, CTrans * c)
{
gint year, month, day;
gdouble TU, TU2, TU3, T0, gmst;
gdouble varep, varpi;
gdouble eccen, epsilon;
gdouble days, M, E, nu, lambnew;
gdouble r0, earth_sun_distance;
gdouble RA, DEC, RA_Moon, DEC_Moon;
gdouble TDT;
gdouble AGE;
gdouble LambdaMoon, BetaMoon, R;
gdouble Ta, Tb, Tc, frac();
gdouble SinGlat, CosGlat, SinGlon, CosGlon, Tau, lmst, x, y, z;
gdouble SinTau, CosTau, SinDec, CosDec;
gdouble TimeNewMoon;
c->UT = UT;
year = (gint) (date / 10000);
month = (gint) ((date - year * 10000) / 100);
day = (gint) (date - year * 10000 - month * 100);
c->year = year;
c->month = month;
c->day = day;
c->doy = DayofYear(year, month, day);
c->dow = DayofWeek(year, month, day, c->dowstr);
/*
* Compute Greenwich Mean Sidereal Time (gmst)
* The TU here is number of Julian centuries
* since 2000 January 1.5
* From the 1996 astronomical almanac
*/
TU = (jd(year, month, day, 0.0) - 2451545.0) / 36525.0;
TU2 = TU * TU;
TU3 = TU2 * TU;
T0 =
(6.0 + 41.0 / 60.0 + 50.54841 / 3600.0) +
8640184.812866 / 3600.0 * TU + 0.093104 / 3600.0 * TU2 -
6.2e-6 / 3600.0 * TU3;
T0 = hour24(T0);
c->gmst = hour24(T0 + UT * 1.002737909);
/* convert to radians for ease later on */
gmst = c->gmst * 15.0 * M_PI / 180.0;
lmst = 24.0 * frac((c->gmst - c->Glon / 15.0) / 24.0);
/*
* Construct Transformation Matrix from GEI to GSE systems
*
*
* First compute:
* mean ecliptic longitude of sun at epoch TU (varep)
* elciptic longitude of perigee at epoch TU (varpi)
* eccentricity of orbit at epoch TU (eccen)
*
* The TU here is the number of Julian centuries since
* 1900 January 0.0 (= 2415020.0)
*/
TDT = UT + 59.0 / 3600.0;
TU = (jd(year, month, day, TDT) - 2415020.0) / 36525.0;
varep =
(279.6966778 + 36000.76892 * TU +
0.0003025 * TU * TU) * RadPerDeg;
varpi =
(281.2208444 + 1.719175 * TU +
0.000452778 * TU * TU) * RadPerDeg;
eccen = 0.01675104 - 0.0000418 * TU - 0.000000126 * TU * TU;
c->eccentricity = eccen;
/*
* Compute the Obliquity of the Ecliptic at epoch TU
* The TU in this formula is the number of Julian
* centuries since epoch 2000 January 1.5
*/
TU = (jd(year, month, day, TDT) - jd(2000, 1, 1, 12.0)) / 36525.0;
epsilon = (23.43929167 - 0.013004166 * TU - 1.6666667e-7 * TU * TU
- 5.0277777778e-7 * TU * TU * TU) * RadPerDeg;
c->epsilon = epsilon;
/*
* Compute:
* Number of Days since epoch 1990.0 (days)
* The Mean Anomaly (M)
* The True Anomaly (nu)
* The Eccentric Anomaly via Keplers equation (E)
*
*
*/
days = jd(year, month, day, TDT) - jd(year, month, day, TDT);
M = angle2pi(2.0 * M_PI / 365.242191 * days + varep - varpi);
E = kepler(M, eccen);
nu =
2.0 * atan(sqrt((1.0 + eccen) / (1.0 - eccen)) * tan(E / 2.0));
lambnew = angle2pi(nu + varpi);
c->lambda_sun = lambnew;
/*
* Compute distance from earth to the sun
*/
r0 = 1.495985e8; /* in km */
earth_sun_distance =
r0 * (1 - eccen * eccen) / (1.0 + eccen * cos(nu)) / 6371.2;
c->earth_sun_dist = earth_sun_distance;
/*
* Compute Right Ascension and Declination of the Sun
*/
RA =
angle360(atan2(sin(lambnew) * cos(epsilon), cos(lambnew)) *
180.0 / M_PI);
DEC = asin(sin(epsilon) * sin(lambnew)) * 180.0 / M_PI;
c->RA_sun = RA;
c->DEC_sun = DEC;
/*
* Compute Moon Phase and AGE Stuff. The AGE that comes out of Moon()
* is actually the Phase converted to days. Since AGE is actually defined
* to be time since last NewMoon, we need to figure out what the JD of the
* last new moon was. Thats done below....
*/
TU = (jd(year, month, day, TDT) - 2451545.0) / 36525.0;
c->MoonPhase = Moon(TU, &LambdaMoon, &BetaMoon, &R, &AGE);
LambdaMoon *= RadPerDeg;
BetaMoon *= RadPerDeg;
RA_Moon =
angle360(atan2
(sin(LambdaMoon) * cos(epsilon) -
tan(BetaMoon) * sin(epsilon),
cos(LambdaMoon)) * DegPerRad);
DEC_Moon =
asin(sin(BetaMoon) * cos(epsilon) +
cos(BetaMoon) * sin(epsilon) * sin(LambdaMoon)) *
DegPerRad;
c->RA_moon = RA_Moon;
c->DEC_moon = DEC_Moon;
/*
* Compute Alt/Az coords
*/
Tau = (15.0 * lmst - RA_Moon) * RadPerDeg;
CosGlat = cos(c->Glat * RadPerDeg);
SinGlat = sin(c->Glat * RadPerDeg);
CosGlon = cos(c->Glon * RadPerDeg);
SinGlon = sin(c->Glon * RadPerDeg);
CosTau = cos(Tau);
SinTau = sin(Tau);
SinDec = sin(DEC_Moon * RadPerDeg);
CosDec = cos(DEC_Moon * RadPerDeg);
x = CosDec * CosTau * SinGlat - SinDec * CosGlat;
y = CosDec * SinTau;
z = CosDec * CosTau * CosGlat + SinDec * SinGlat;
c->A_moon = DegPerRad * atan2(y, x) + 180.0;
c->h_moon = DegPerRad * asin(z);
c->Visible = (c->h_moon < 0.0) ? FALSE : TRUE;
/*
* Compute accurate AGE of the Moon
*/
Tb = TU - AGE / 36525.0; /* should be very close to minimum */
Ta = Tb - 0.4 / 36525.0;
Tc = Tb + 0.4 / 36525.0;
c->MoonAge = (TU - NewMoon(Ta, Tb, Tc)) * 36525.0;
/* g_message("ta is %f, tb is %f, tc is %f, moonage is %f, age is %f", Ta, Tb, Tc, c->MoonAge, AGE); */
/*
* Compute next New Moon
*/
/* New Moon very sensitive to initial parameters. must find correct ones. */
/* g_message("abs(MoonPhase) is %f, ratio is %f\n", ABS(c->MoonPhase), c->MoonAge/c->MoonPhase); */
/* hardcoded */
/* TimeNewMoon = 29.530589; */
/* estimated for non-small phases */
TimeNewMoon = (ABS(c->MoonPhase) < 0.6) ? 29.530589 : c->MoonAge/c->MoonPhase;
Tb += TimeNewMoon/36525.0;
Ta += TimeNewMoon/36525.0;
Tc += TimeNewMoon/36525.0;
c->NewMoon = (NewMoon(Ta, Tb, Tc) - TU) * 36525.0;
/* g_message("calculated Moonperiod is %f\n", TimeNewMoon); */
/* g_message("ta is %f, tb is %f, tc is %f, newmoon is %f\n", Ta, Tb, Tc, c->NewMoon); */
/* approximate FullMoon */
c->FullMoon = (((ABS(c->MoonPhase) < 0.5) ? 0.5 : 1.5) - c->MoonPhase) * 29.530589;
/* g_message("fullmoon in %f days; or %f days\n", c->FullMoon, (c->NewMoon+(29.530589/2.0))); */
/*
* Set Earth-Moon distance (calc above w/ func Moon)
*/
c->EarthMoonDistance = R;
c->SinGlat = SinGlat;
c->CosGlat = CosGlat;
}
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