/*
* given a particular time (expressed in seconds since the unix
* epoch), compute position on the earth (lat, lon) such that sun is
* directly overhead.
*/
void sun_position(time_t ssue, double *lat, double *lon)
//time_t ssue; /* seconds since unix epoch */
//double *lat; /* (return) latitude */
//double *lon; /* (return) longitude */
{
double lambda;
double alpha, delta;
double tmp;
lambda = sun_ecliptic_longitude(ssue);
ecliptic_to_equatorial(lambda, 0.0, &alpha, &delta);
tmp = alpha - (TWOPI/24)*GST(ssue);
if (tmp < -M_PI)
{
do tmp += TWOPI;
while (tmp < -M_PI);
}
else if (tmp > M_PI)
{
do tmp -= TWOPI;
while (tmp < -M_PI);
}
*lon = tmp * (360/TWOPI);
*lat = delta * (360/TWOPI);
}
/* Calculate the position of the sun at a given time. pages 89-91 */
void
sun_position (time_t unix_time, gdouble *lat, gdouble *lon)
{
gdouble jd, D, N, M, E, x, v, lambda;
gdouble ra, dec;
jd = unix_time_to_julian_date (unix_time);
/* Calculate number of days since the epoch */
D = jd - EPOCH;
N = D*360/365.242191;
/* normalize to 0 - 360 degrees */
NORMALIZE (N);
/* Step 4: */
M = N + EPSILON_G - MU_G;
NORMALIZE (M);
/* Step 5: convert to radians */
M = DEG_TO_RADS (M);
/* Step 6: */
E = solve_keplers_equation (ECCENTRICITY, M);
/* Step 7: */
x = sqrt ((1 + ECCENTRICITY)/(1 - ECCENTRICITY)) * tan (E/2);
/* Step 8, 9 */
v = 2 * RADS_TO_DEG (atan (x));
NORMALIZE (v);
/* Step 10 */
lambda = v + MU_G;
NORMALIZE (lambda);
/* convert the ecliptic longitude to right ascension and declination */
ecliptic_to_equatorial (DEG_TO_RADS (lambda), 0.0, &ra, &dec);
ra = ra - (G_PI/12) * greenwich_sidereal_time (unix_time);
ra = RADS_TO_DEG (ra);
dec = RADS_TO_DEG (dec);
NORMALIZE (ra);
NORMALIZE (dec);
*lat = dec;
*lon = ra;
}
/*
* given a particular time (expressed in seconds since the unix
* epoch), compute position on the earth (lat, lon) such that sun is
* directly overhead.
*/
void sun_position(time_t ssue, double *lat, double *lon)
/* time_t ssue; seconds since unix epoch */
/* double *lat; (return) latitude in rad */
/* double *lon; (return) longitude in rad */
{
double lambda;
double alpha, delta;
double tmp;
lambda = sun_ecliptic_longitude(ssue);
ecliptic_to_equatorial(lambda, 0.0, &alpha, &delta);
tmp = alpha - (TWOPI / 24) * GST(ssue);
Normalize(tmp);
*lon = tmp;
*lat = delta;
}
/*
* given a particular time (expressed in seconds since the unix
* epoch), compute position on the earth (lat, lon) such that the
* moon is directly overhead.
*
* Based on duffett-smith **2nd ed** section 61; combines some steps
* into single expressions to reduce the number of extra variables.
*/
void moon_position(time_t ssue, double *lat, double *lon)
/* time_t ssue; seconds since unix epoch */
/* double *lat; (return) latitude in ra */
/* double *lon; (return) longitude in ra */
{
double lambda, beta;
double D, L, Ms, Mm, N, Ev, Ae, Ec, alpha, delta;
D = DaysSinceEpoch(ssue);
lambda = sun_ecliptic_longitude(ssue);
Ms = mean_sun(D);
L = fmod(D / SideralMonth, 1.0) * TWOPI + MoonMeanLongitude;
Normalize(L);
Mm = L - DegsToRads(0.1114041 * D) - MoonMeanLongitudePerigee;
Normalize(Mm);
N = MoonMeanLongitudeNode - DegsToRads(0.0529539 * D);
Normalize(N);
Ev = DegsToRads(1.2739) * sin(2.0 * (L - lambda) - Mm);
Ae = DegsToRads(0.1858) * sin(Ms);
Mm += Ev - Ae - DegsToRads(0.37) * sin(Ms);
Ec = DegsToRads(6.2886) * sin(Mm);
L += Ev + Ec - Ae + DegsToRads(0.214) * sin(2.0 * Mm);
L += DegsToRads(0.6583) * sin(2.0 * (L - lambda));
N -= DegsToRads(0.16) * sin(Ms);
L -= N;
lambda = (fabs(cos(L)) < 1e-12) ?
(N + sin(L) * cos(MoonInclination) * PI / 2) :
(N + atan2(sin(L) * cos(MoonInclination), cos(L)));
Normalize(lambda);
beta = asin(sin(L) * sin(MoonInclination));
ecliptic_to_equatorial(lambda, beta, &alpha, &delta);
alpha -= (TWOPI / 24) * GST(ssue);
Normalize(alpha);
*lon = alpha;
*lat = delta;
}
