pom/pom.c

   1 /*      $NetBSD: pom.c,v 1.6 1996/02/06 22:47:29 jtc Exp $      */
   2
   3 /*
   4  * Copyright (c) 1989, 1993
   5  *      The Regents of the University of California.  All rights reserved.
   6  *
   7  * This code is derived from software posted to USENET.
   8  *
   9  * Redistribution and use in source and binary forms, with or without
  10  * modification, are permitted provided that the following conditions
  11  * are met:
  12  * 1. Redistributions of source code must retain the above copyright
  13  *    notice, this list of conditions and the following disclaimer.
  14  * 2. Redistributions in binary form must reproduce the above copyright
  15  *    notice, this list of conditions and the following disclaimer in the
  16  *    documentation and/or other materials provided with the distribution.
  17  * 3. All advertising materials mentioning features or use of this software
  18  *    must display the following acknowledgement:
  19  *      This product includes software developed by the University of
  20  *      California, Berkeley and its contributors.
  21  * 4. Neither the name of the University nor the names of its contributors
  22  *    may be used to endorse or promote products derived from this software
  23  *    without specific prior written permission.
  24  *
  25  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  26  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  27  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  28  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  29  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  30  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  31  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  32  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  33  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  34  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  35  * SUCH DAMAGE.
  36  */
  37
  38 #ifndef lint
  39 static char copyright[] =
  40 "@(#) Copyright (c) 1989, 1993\n\
  41         The Regents of the University of California.  All rights reserved.\n";
  42 #endif /* not lint */
  43
  44 #ifndef lint
  45 #if 0
  46 static char sccsid[] = "@(#)pom.c       8.1 (Berkeley) 5/31/93";
  47 #else
  48 static char rcsid[] = "$NetBSD: pom.c,v 1.6 1996/02/06 22:47:29 jtc Exp $";
  49 #endif
  50 #endif /* not lint */
  51
  52 /*
  53  * Phase of the Moon.  Calculates the current phase of the moon.
  54  * Based on routines from `Practical Astronomy with Your Calculator',
  55  * by Duffett-Smith.  Comments give the section from the book that
  56  * particular piece of code was adapted from.
  57  *
  58  * -- Keith E. Brandt  VIII 1984
  59  *
  60  */
  61
  62 #include <sys/time.h>
  63 #include <stdio.h>
  64 #include <string.h>
  65 #include <tzfile.h>
  66 #include <math.h>
  67 #include <errno.h>
  68
  69 #define PI        3.141592654
  70 #define EPOCH     85
  71 #define EPSILONg  279.611371    /* solar ecliptic long at EPOCH */
  72 #define RHOg      282.680403    /* solar ecliptic long of perigee at EPOCH */
  73 #define ECCEN     0.01671542    /* solar orbit eccentricity */
  74 #define lzero     18.251907     /* lunar mean long at EPOCH */
  75 #define Pzero     192.917585    /* lunar mean long of perigee at EPOCH */
  76 #define Nzero     55.204723     /* lunar mean long of node at EPOCH */
  77
  78 double dtor(), potm(), adj360();
  79
  80 main()
  81 {
  82         struct timeval tp;
  83         struct timezone tzp;
  84         struct tm *GMT, *gmtime();
  85         time_t tmpt;
  86         double days, today, tomorrow;
  87         int cnt;
  88
  89         if (gettimeofday(&tp,&tzp)) {
  90                 (void)fprintf(stderr, "pom: %s\n", strerror(errno));
  91                 exit(1);
  92         }
  93         tmpt = tp.tv_sec;
  94         GMT = gmtime(&tmpt);
  95         days = (GMT->tm_yday + 1) + ((GMT->tm_hour +
  96             (GMT->tm_min / 60.0) + (GMT->tm_sec / 3600.0)) / 24.0);
  97         for (cnt = EPOCH; cnt < GMT->tm_year; ++cnt)
  98                 days += isleap(cnt) ? 366 : 365;
  99         today = potm(days) + .5;
 100         (void)printf("The Moon is ");
 101         if ((int)today == 100)
 102                 (void)printf("Full\n");
 103         else if (!(int)today)
 104                 (void)printf("New\n");
 105         else {
 106                 tomorrow = potm(days + 1);
 107                 if ((int)today == 50)
 108                         (void)printf("%s\n", tomorrow > today ?
 109                             "at the First Quarter" : "at the Last Quarter");
 110                 else {
 111                         (void)printf("%s ", tomorrow > today ?
 112                             "Waxing" : "Waning");
 113                         if (today > 50)
 114                                 (void)printf("Gibbous (%1.0f%% of Full)\n",
 115                                     today);
 116                         else if (today < 50)
 117                                 (void)printf("Crescent (%1.0f%% of Full)\n",
 118                                     today);
 119                 }
 120         }
 121         exit(0);
 122 }
 123
 124 /*
 125  * potm --
 126  *      return phase of the moon
 127  */
 128 double
 129 potm(days)
 130         double days;
 131 {
 132         double N, Msol, Ec, LambdaSol, l, Mm, Ev, Ac, A3, Mmprime;
 133         double A4, lprime, V, ldprime, D, Nm;
 134
 135         N = 360 * days / 365.2422;                              /* sec 42 #3 */
 136         adj360(&N);
 137         Msol = N + EPSILONg - RHOg;                             /* sec 42 #4 */
 138         adj360(&Msol);
 139         Ec = 360 / PI * ECCEN * sin(dtor(Msol));                /* sec 42 #5 */
 140         LambdaSol = N + Ec + EPSILONg;                          /* sec 42 #6 */
 141         adj360(&LambdaSol);
 142         l = 13.1763966 * days + lzero;                          /* sec 61 #4 */
 143         adj360(&l);
 144         Mm = l - (0.1114041 * days) - Pzero;                    /* sec 61 #5 */
 145         adj360(&Mm);
 146         Nm = Nzero - (0.0529539 * days);                        /* sec 61 #6 */
 147         adj360(&Nm);
 148         Ev = 1.2739 * sin(dtor(2*(l - LambdaSol) - Mm));        /* sec 61 #7 */
 149         Ac = 0.1858 * sin(dtor(Msol));                          /* sec 61 #8 */
 150         A3 = 0.37 * sin(dtor(Msol));
 151         Mmprime = Mm + Ev - Ac - A3;                            /* sec 61 #9 */
 152         Ec = 6.2886 * sin(dtor(Mmprime));                       /* sec 61 #10 */
 153         A4 = 0.214 * sin(dtor(2 * Mmprime));                    /* sec 61 #11 */
 154         lprime = l + Ev + Ec - Ac + A4;                         /* sec 61 #12 */
 155         V = 0.6583 * sin(dtor(2 * (lprime - LambdaSol)));       /* sec 61 #13 */
 156         ldprime = lprime + V;                                   /* sec 61 #14 */
 157         D = ldprime - LambdaSol;                                /* sec 63 #2 */
 158         return(50 * (1 - cos(dtor(D))));                        /* sec 63 #3 */
 159 }
 160
 161 /*
 162  * dtor --
 163  *      convert degrees to radians
 164  */
 165 double
 166 dtor(deg)
 167         double deg;
 168 {
 169         return(deg * PI / 180);
 170 }
 171
 172 /*
 173  * adj360 --
 174  *      adjust value so 0 <= deg <= 360
 175  */
 176 double
 177 adj360(deg)
 178         double *deg;
 179 {
 180         for (;;)
 181                 if (*deg < 0)
 182                         *deg += 360;
 183                 else if (*deg > 360)
 184                         *deg -= 360;
 185                 else
 186                         break;
 187 }