path: root/kmoon/phases.cpp

/* This file is part of the kmoon application with explicit permission by the author
    Copyright (C) 1996 Christopher Osburn

    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Library General Public
    License as published by the Free Software Foundation; either
    version 2 of the License, or (at your option) any later version.

    This library 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
    Library General Public License for more details.

    You should have received a copy of the GNU Library General Public License
    along with this library; see the file COPYING.LIB.  If not, write to
    the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
    Boston, MA 02110-1301, USA.
*/
/*
** jd.c:
** 1996/02/11
**
** Copyright 1996, Christopher Osburn, Lunar Outreach Services,
** Non-commercial usage license granted to all.
**
** convert a Julian Day number to a struct tm
**
** Parameter:
**   double jd:  Julian day number with fraction of day
**
** Returns:
**   struct tm *event_date:  Date-time group holding year, month, day, hour,
**                and minute of the event
*/

#include <time.h>
#include <stdlib.h>

time_t JDtoDate(double jd, struct tm *event_date)
/* convert a Julian Date to a date-time group */
{
  long a, a1, z, b, c, d, e;
  double f, day;
  struct tm dummy;
  if ( !event_date )
      event_date = &dummy;

  jd += 0.5;
  z = (long) jd;
  f = jd - z;

  if (z < 2299161)
  {
    a = z;
  }
  else
  {
    a1 = (long) ((z - 1867216.25) / 36524.25);
    a = z + 1 + a1 - (long)(a1 / 4);
  }

  b = a + 1524;
  c = (long)((b - 122.1) / 365.25);
  d = (long)(365.25 * c);
  e = (long)((b - d)/30.6001);

  day = b - d - (long)(30.6001 * e) + f;

  if (e < 14)
  {
    event_date->tm_mon = (e - 1) - 1;
  }
  else
  {
    event_date->tm_mon = (e - 13) - 1;
  }

  if (event_date->tm_mon > (2 - 1))
  {
    event_date->tm_year = c - 4716 - 1900;
  }
  else
  {
    event_date->tm_year = c - 4715 - 1900;
  }
  event_date->tm_mday = (int)day;
  day -= event_date->tm_mday;
  day *= 24;
  event_date->tm_hour = (int)day;
  day -= event_date->tm_hour;
  day *= 60;
  event_date->tm_min = (int)day;
  day -= event_date->tm_min;
  day *= 60;
  event_date->tm_sec = (int)day;

  event_date->tm_isdst = -1;

  return mktime(event_date);
}

double DatetoJD(struct tm *event_date)
/* convert a date-time group to a JD with fraction */
{
  int y, m;
  double d;
  int a, b;
  double jd;

  y = event_date->tm_year + 1900;
  m = event_date->tm_mon + 1;
  d = (double)(event_date->tm_mday) + (event_date->tm_hour / 24.0)
    + (event_date->tm_min / 1440.0) + (event_date->tm_sec / 86400.0);

  if (m == 1 || m == 2)
  {
    y--;
    m += 12;
  }

  a = (int)(y / 100);
  b = 2 - a + (int)(a / 4);

  if (y < 1583)
    if ((y < 1582) || (m < 10) || ((m == 10) && (d <= 15)))
      b = 0;

  jd = (long)(365.25 * (y + 4716)) + (long)(30.6001 * (m+1))
     + d + b - 1524.5;

  return jd;
}

/*
** misc.h
** 1996/02/11
**
** Copyright 1996, Christopher Osburn, Lunar Outreach Services,
** Non-commercial usage license granted to all.
**
** Miscellaneous routines for moon phase programs
**
*/

#include <math.h>

double torad(double x)
/* convert x to radians */
{
  x = fmod(x, 360.0); /* normalize the angle */
  return ((x) * 0.01745329251994329576);
                    /* and return the result */
}

/*
** moonphase.c
** 1996/02/11
**
** Copyright 1996, Christopher Osburn, Lunar Outreach Services,
** Non-commercial usage license granted to all.
**
** calculate phase of the moon per Meeus Ch. 47
**
** Parameters:
**    int lun:  phase parameter.  This is the number of lunations
**              since the New Moon of 2000 January 6.
**
**    int phi:  another phase parameter, selecting the phase of the
**              moon.  0 = New, 1 = First TQtr, 2 = Full, 3 = Last TQtr
**
** Return:  Apparent JD of the needed phase
*/

#include <stdio.h>
#include <math.h>

double moonphase(double k, int phi)
{
  int i;                       /* iterator to be named later.  Every
                                  program needs an i */
  double T;                    /* time parameter, Julian Centuries since
                                  J2000 */
  double JDE;                  /* Julian Ephemeris Day of phase event */
  double E;                    /* Eccentricity anomaly */
  double M;                    /* Sun's mean anomaly */
  double M1;                   /* Moon's mean anomaly */
  double F;                    /* Moon's argument of latitude */
  double O;                    /* Moon's longitude of ascenfing node */
  double A[15];                /* planetary arguments */
  double W;                    /* added correction for quarter phases */

  T = k / 1236.85;                            /* (47.3) */

  /* this is the first approximation.  all else is for style points! */
  JDE = 2451550.09765 + (29.530588853 * k)    /* (47.1) */
        + T * T * (0.0001337 + T * (-0.000000150 + 0.00000000073 * T));

  /* these are correction parameters used below */
  E = 1.0                                     /* (45.6) */
      + T * (-0.002516 + -0.0000074 * T);
  M = 2.5534 + 29.10535669 * k                /* (47.4) */
      + T * T * (-0.0000218 + -0.00000011 * T);
  M1 = 201.5643 + 385.81693528 * k            /* (47.5) */
       + T * T * (0.0107438 + T * (0.00001239 + -0.000000058 * T));
  F = 160.7108 + 390.67050274 * k             /* (47.6) */
      + T * T * (-0.0016341 * T * (-0.00000227 + 0.000000011 * T));
  O = 124.7746 - 1.56375580 * k               /* (47.7) */
      + T * T * (0.0020691 + 0.00000215 * T);

  /* planetary arguments */
  A[0]  = 0; /* unused! */
  A[1]  = 299.77 +  0.107408 * k - 0.009173 * T * T;
  A[2]  = 251.88 +  0.016321 * k;
  A[3]  = 251.83 + 26.651886 * k;
  A[4]  = 349.42 + 36.412478 * k;
  A[5]  =  84.66 + 18.206239 * k;
  A[6]  = 141.74 + 53.303771 * k;
  A[7]  = 207.14 +  2.453732 * k;
  A[8]  = 154.84 +  7.306860 * k;
  A[9]  =  34.52 + 27.261239 * k;
  A[10] = 207.19 +  0.121824 * k;
  A[11] = 291.34 +  1.844379 * k;
  A[12] = 161.72 + 24.198154 * k;
  A[13] = 239.56 + 25.513099 * k;
  A[14] = 331.55 +  3.592518 * k;

  /* all of the above crap must be made into radians!!! */
  /* except for E... */

  M = torad(M);
  M1 = torad(M1);
  F = torad(F);
  O = torad(O);

  /* all those planetary arguments, too! */
  for (i=1; i<=14; i++)
    A[i] = torad(A[i]);

  /* ok, we have all the parameters, let's apply them to the JDE.
    (remember the JDE?  this is a program about the JDE...)        */

  switch(phi)
  {
    /* a special case for each different phase.  NOTE!,
       I'm not treating these in a 0123 order!!!  Pay
       attention, there,  you!                         */

    case 0: /* New Moon */
      JDE = JDE
          - 0.40720         * sin (M1)
          + 0.17241 * E     * sin (M)
          + 0.01608         * sin (2.0 * M1)
          + 0.01039         * sin (2.0 * F)
          + 0.00739 * E     * sin (M1 - M)
          - 0.00514 * E     * sin (M1 + M)
          + 0.00208 * E * E * sin (2.0 * M)
          - 0.00111         * sin (M1 - 2.0 * F)
          - 0.00057         * sin (M1 + 2.0 * F)
          + 0.00056 * E     * sin (2.0 * M1 + M)
          - 0.00042         * sin (3.0 * M1)
          + 0.00042 * E     * sin (M + 2.0 * F)
          + 0.00038 * E     * sin (M - 2.0 * F)
          - 0.00024 * E     * sin (2.0 * M1 - M)
          - 0.00017         * sin (O)
          - 0.00007         * sin (M1 + 2.0 * M)
          + 0.00004         * sin (2.0 * M1 - 2.0 * F)
          + 0.00004         * sin (3.0 * M)
          + 0.00003         * sin (M1 + M - 2.0 * F)
          + 0.00003         * sin (2.0 * M1 + 2.0 * F)
          - 0.00003         * sin (M1 + M + 2.0 * F)
          + 0.00003         * sin (M1 - M + 2.0 * F)
          - 0.00002         * sin (M1 - M - 2.0 * F)
          - 0.00002         * sin (3.0 * M1 + M)
          + 0.00002         * sin (4.0 * M1);

          break;

    case 2: /* Full Moon */
      JDE = JDE
          - 0.40614         * sin (M1)
          + 0.17302 * E     * sin (M)
          + 0.01614         * sin (2.0 * M1)
          + 0.01043         * sin (2.0 * F)
          + 0.00734 * E     * sin (M1 - M)
          - 0.00515 * E     * sin (M1 + M)
          + 0.00209 * E * E * sin (2.0 * M)
          - 0.00111         * sin (M1 - 2.0 * F)
          - 0.00057         * sin (M1 + 2.0 * F)
          + 0.00056 * E     * sin (2.0 * M1 + M)
          - 0.00042         * sin (3.0 * M1)
          + 0.00042 * E     * sin (M + 2.0 * F)
          + 0.00038 * E     * sin (M - 2.0 * F)
          - 0.00024 * E     * sin (2.0 * M1 - M)
          - 0.00017         * sin (O)
          - 0.00007         * sin (M1 + 2.0 * M)
          + 0.00004         * sin (2.0 * M1 - 2.0 * F)
          + 0.00004         * sin (3.0 * M)
          + 0.00003         * sin (M1 + M - 2.0 * F)
          + 0.00003         * sin (2.0 * M1 + 2.0 * F)
          - 0.00003         * sin (M1 + M + 2.0 * F)
          + 0.00003         * sin (M1 - M + 2.0 * F)
          - 0.00002         * sin (M1 - M - 2.0 * F)
          - 0.00002         * sin (3.0 * M1 + M)
          + 0.00002         * sin (4.0 * M1);

          break;

    case 1: /* First Quarter */
    case 3: /* Last Quarter */
      JDE = JDE
          - 0.62801         * sin (M1)
          + 0.17172 * E     * sin (M)
          - 0.01183 * E     * sin (M1 + M)
          + 0.00862         * sin (2.0 * M1)
          + 0.00804         * sin (2.0 * F)
          + 0.00454 * E     * sin (M1 - M)
          + 0.00204 * E * E * sin (2.0 * M)
          - 0.00180         * sin (M1 - 2.0 * F)
          - 0.00070         * sin (M1 + 2.0 * F)
          - 0.00040         * sin (3.0 * M1)
          - 0.00034 * E     * sin (2.0 * M1 - M)
          + 0.00032 * E     * sin (M + 2.0 * F)
          + 0.00032 * E     * sin (M - 2.0 * F)
          - 0.00028 * E * E * sin (M1 + 2.0 * M)
          + 0.00027 * E     * sin (2.0 * M1 + M)
          - 0.00017         * sin (O)
          - 0.00005         * sin (M1 - M - 2.0 * F)
          + 0.00004         * sin (2.0 * M1 + 2.0 * F)
          - 0.00004         * sin (M1 + M + 2.0 * F)
          + 0.00004         * sin (M1 - 2.0 * M)
          + 0.00003         * sin (M1 + M - 2.0 * F)
          + 0.00003         * sin (3.0 * M)
          + 0.00002         * sin (2.0 * M1 - 2.0 * F)
          + 0.00002         * sin (M1 - M + 2.0 * F)
          - 0.00002         * sin (3.0 * M1 + M);

      W = 0.00306
        - 0.00038 * E * cos(M)
        + 0.00026 * cos(M1)
        - 0.00002 * cos(M1 - M)
        + 0.00002 * cos(M1 + M)
        + 0.00002 * cos(2.0 * F);
      if (phi == 3)
        W = -W;
      JDE += W;

      break;

    default: /* oops! */
      fprintf(stderr, "The Moon has exploded!\n");
      exit(1);
      break; /* unexecuted code */
  }
      /* now there are some final correction to everything */
  JDE = JDE
      + 0.000325 * sin(A[1])
      + 0.000165 * sin(A[2])
      + 0.000164 * sin(A[3])
      + 0.000126 * sin(A[4])
      + 0.000110 * sin(A[5])
      + 0.000062 * sin(A[6])
      + 0.000060 * sin(A[7])
      + 0.000056 * sin(A[8])
      + 0.000047 * sin(A[9])
      + 0.000042 * sin(A[10])
      + 0.000040 * sin(A[11])
      + 0.000037 * sin(A[12])
      + 0.000035 * sin(A[13])
      + 0.000023 * sin(A[14]);

  return JDE;
}

#define LUNATION_OFFSET 953

double moonphasebylunation(int lun, int phi)
{
    double k;

    k = lun - LUNATION_OFFSET + phi / 4.0;
    return moonphase(k, phi);
}