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enlightenment-module-moon/src/CalcEphem.c

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#include <math.h>
#include <string.h>
#include "CalcEphem.h"
int DayofYear(int, int, int);
int DayofWeek(int, int, int, char[]);
double kepler(double, double);
double jd(int, int, int, double);
double hour24(double);
double angle2pi(double);
double angle360(double);
void Radec_to_Cart(double, double, Vector *);
int LeapYear(int);
int DayofYear(year, month, day)
int year, month, day;
{
double jd();
return((int)(jd(year, month, day, 0.0) - jd(year, 1, 0, 0.0)));
}
int DayofWeek(year, month, day, dowstr)
int year, month, day;
char dowstr[];
{
double JD, A, Afrac, jd();
int n, iA;
JD = jd(year, month, day, 0.0);
A = (JD + 1.5)/7.0;
iA = (int)A;
Afrac = A - (double)iA;
n = (int)(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);
}
void
CalcEphem(date, UT, c)
long int date; /* integer containing the date (e.g. 960829) */
double UT; /* Universal Time */
CTrans *c; /* structure containing all the relevent coord trans info */
{
int year, month, day;
double TU, TU2, TU3, T0, gmst;
double varep, varpi;
double eccen, epsilon;
double days, M, E, nu, lambnew;
double r0, earth_sun_distance;
double RA, DEC, RA_Moon, DEC_Moon;
double TDT;
double AGE;
double LambdaMoon, BetaMoon, R;
double jd(), hour24(), angle2pi(), angle360(), kepler(), Moon(), NewMoon();
double Ta, Tb, Tc, frac();
double SinGlat, CosGlat, SinGlon, CosGlon, Tau, lmst, x, y, z;
double SinTau, CosTau, SinDec, CosDec;
c->UT = UT;
year = (int)(date/10000);
month = (int)( (date - year*10000)/100 );
day = (int)( 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);
c->h_moon = DegPerRad*asin(z);
c->Visible = (c->h_moon < 0.0) ? 0 : 1;
/*
* 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;
/*
* Compute Earth-Moon distance
*/
c->EarthMoonDistance = R;
}
double kepler(M, e)
double M, e;
{
int n=0;
double 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);
}
/*
* Compute the Julian Day number for the given date.
* Julian Date is the number of days since noon of Jan 1 4713 B.C.
*/
double jd(ny, nm, nd, UT)
int ny, nm, nd;
double UT;
{
double A, B, C, D, JD, day;
day = nd + UT/24.0;
if ((nm == 1) || (nm == 2)){
ny = ny - 1;
nm = nm + 12;
}
if (((double)ny+nm/12.0+day/365.25)>=(1582.0+10.0/12.0+15.0/365.25)){
A = ((int)(ny / 100.0));
B = 2.0 - A + (int)(A/4.0);
}
else{
B = 0.0;
}
if (ny < 0.0){
C = (int)((365.25*(double)ny) - 0.75);
}
else{
C = (int)(365.25*(double)ny);
}
D = (int)(30.6001*(double)(nm+1));
JD = B + C + D + day + 1720994.5;
return(JD);
}
double hour24(hour)
double hour;
{
int n;
if (hour < 0.0){
n = (int)(hour/24.0) - 1;
return(hour-n*24.0);
}
else if (hour > 24.0){
n = (int)(hour/24.0);
return(hour-n*24.0);
}
else{
return(hour);
}
}
double angle2pi(angle)
double angle;
{
int n;
double a;
a = 2.0*M_PI;
if (angle < 0.0){
n = (int)(angle/a) - 1;
return(angle-n*a);
}
else if (angle > a){
n = (int)(angle/a);
return(angle-n*a);
}
else{
return(angle);
}
}
double angle360(angle)
double angle;
{
int n;
if (angle < 0.0){
n = (int)(angle/360.0) - 1;
return(angle-n*360.0);
}
else if (angle > 360.0){
n = (int)(angle/360.0);
return(angle-n*360.0);
}
else{
return(angle);
}
}
void
Radec_to_Cart(ra, dec, r)
double ra, dec; /* RA and DEC */
Vector *r; /* returns corresponding cartesian unit vector */
{
/*
* Convert ra/dec from degrees to radians
*/
ra *= RadPerDeg;
dec *= RadPerDeg;
/*
* Compute cartesian coordinates (in GEI)
*/
r->x = cos(dec) * cos(ra);
r->y = cos(dec) * sin(ra);
r->z = sin(dec);
}
int LeapYear(year)
int year;
{
if ((year%100 == 0)&&(year%400 != 0)) return(0);
else if (year%4 == 0) return(1);
else return(0);
}
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