pom/pom.c

   1 /*
   2  * Copyright (c) 1989 The Regents of the University of California.
   3  * All rights reserved.
   4  *
   5  * This code is derived from software posted to USENET.
   6  *
   7  * Redistribution and use in source and binary forms, with or without
   8  * modification, are permitted provided that the following conditions
   9  * are met:
  10  * 1. Redistributions of source code must retain the above copyright
  11  *    notice, this list of conditions and the following disclaimer.
  12  * 2. Redistributions in binary form must reproduce the above copyright
  13  *    notice, this list of conditions and the following disclaimer in the
  14  *    documentation and/or other materials provided with the distribution.
  15  * 3. All advertising materials mentioning features or use of this software
  16  *    must display the following acknowledgement:
  17  *      This product includes software developed by the University of
  18  *      California, Berkeley and its contributors.
  19  * 4. Neither the name of the University nor the names of its contributors
  20  *    may be used to endorse or promote products derived from this software
  21  *    without specific prior written permission.
  22  *
  23  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  24  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  25  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  26  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  27  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  28  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  29  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  30  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  31  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  32  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  33  * SUCH DAMAGE.
  34  */
  35
  36 #ifndef lint
  37 char copyright[] =
  38 "@(#) Copyright (c) 1989 The Regents of the University of California.\n\
  39  All rights reserved.\n";
  40 #endif /* not lint */
  41
  42 #ifndef lint
  43 /*static char sccsid[] = "from: @(#)pom.c       5.3 (Berkeley) 2/28/91";*/
  44 static char rcsid[] = "$Id: pom.c,v 1.3 1995/02/03 18:15:02 jtc Exp $";
  45 #endif /* not lint */
  46
  47 /*
  48  * Phase of the Moon.  Calculates the current phase of the moon.
  49  * Based on routines from `Practical Astronomy with Your Calculator',
  50  * by Duffett-Smith.  Comments give the section from the book that
  51  * particular piece of code was adapted from.
  52  *
  53  * -- Keith E. Brandt  VIII 1984
  54  *
  55  */
  56
  57 #include <sys/time.h>
  58 #include <stdio.h>
  59 #include <string.h>
  60 #include <tzfile.h>
  61 #include <math.h>
  62
  63 #define PI        3.141592654
  64 #define EPOCH     85
  65 #define EPSILONg  279.611371    /* solar ecliptic long at EPOCH */
  66 #define RHOg      282.680403    /* solar ecliptic long of perigee at EPOCH */
  67 #define ECCEN     0.01671542    /* solar orbit eccentricity */
  68 #define lzero     18.251907     /* lunar mean long at EPOCH */
  69 #define Pzero     192.917585    /* lunar mean long of perigee at EPOCH */
  70 #define Nzero     55.204723     /* lunar mean long of node at EPOCH */
  71
  72 double dtor(), potm(), adj360();
  73
  74 main()
  75 {
  76         extern int errno;
  77         struct timeval tp;
  78         struct timezone tzp;
  79         struct tm *GMT, *gmtime();
  80         double days, today, tomorrow;
  81         int cnt;
  82
  83         if (gettimeofday(&tp,&tzp)) {
  84                 (void)fprintf(stderr, "pom: %s\n", strerror(errno));
  85                 exit(1);
  86         }
  87         GMT = gmtime(&tp.tv_sec);
  88         days = (GMT->tm_yday + 1) + ((GMT->tm_hour +
  89             (GMT->tm_min / 60.0) + (GMT->tm_sec / 3600.0)) / 24.0);
  90         for (cnt = EPOCH; cnt < GMT->tm_year; ++cnt)
  91                 days += isleap(cnt) ? 366 : 365;
  92         today = potm(days) + .5;
  93         (void)printf("The Moon is ");
  94         if ((int)today == 100)
  95                 (void)printf("Full\n");
  96         else if (!(int)today)
  97                 (void)printf("New\n");
  98         else {
  99                 tomorrow = potm(days + 1);
 100                 if ((int)today == 50)
 101                         (void)printf("%s\n", tomorrow > today ?
 102                             "at the First Quarter" : "at the Last Quarter");
 103                 else {
 104                         (void)printf("%s ", tomorrow > today ?
 105                             "Waxing" : "Waning");
 106                         if (today > 50)
 107                                 (void)printf("Gibbous (%1.0f%% of Full)\n",
 108                                     today);
 109                         else if (today < 50)
 110                                 (void)printf("Crescent (%1.0f%% of Full)\n",
 111                                     today);
 112                 }
 113         }
 114         exit(0);
 115 }
 116
 117 /*
 118  * potm --
 119  *      return phase of the moon
 120  */
 121 double
 122 potm(days)
 123         double days;
 124 {
 125         double N, Msol, Ec, LambdaSol, l, Mm, Ev, Ac, A3, Mmprime;
 126         double A4, lprime, V, ldprime, D, Nm;
 127
 128         N = 360 * days / 365.2422;                              /* sec 42 #3 */
 129         adj360(&N);
 130         Msol = N + EPSILONg - RHOg;                             /* sec 42 #4 */
 131         adj360(&Msol);
 132         Ec = 360 / PI * ECCEN * sin(dtor(Msol));                /* sec 42 #5 */
 133         LambdaSol = N + Ec + EPSILONg;                          /* sec 42 #6 */
 134         adj360(&LambdaSol);
 135         l = 13.1763966 * days + lzero;                          /* sec 61 #4 */
 136         adj360(&l);
 137         Mm = l - (0.1114041 * days) - Pzero;                    /* sec 61 #5 */
 138         adj360(&Mm);
 139         Nm = Nzero - (0.0529539 * days);                        /* sec 61 #6 */
 140         adj360(&Nm);
 141         Ev = 1.2739 * sin(dtor(2*(l - LambdaSol) - Mm));        /* sec 61 #7 */
 142         Ac = 0.1858 * sin(dtor(Msol));                          /* sec 61 #8 */
 143         A3 = 0.37 * sin(dtor(Msol));
 144         Mmprime = Mm + Ev - Ac - A3;                            /* sec 61 #9 */
 145         Ec = 6.2886 * sin(dtor(Mmprime));                       /* sec 61 #10 */
 146         A4 = 0.214 * sin(dtor(2 * Mmprime));                    /* sec 61 #11 */
 147         lprime = l + Ev + Ec - Ac + A4;                         /* sec 61 #12 */
 148         V = 0.6583 * sin(dtor(2 * (lprime - LambdaSol)));       /* sec 61 #13 */
 149         ldprime = lprime + V;                                   /* sec 61 #14 */
 150         D = ldprime - LambdaSol;                                /* sec 63 #2 */
 151         return(50 * (1 - cos(dtor(D))));                        /* sec 63 #3 */
 152 }
 153
 154 /*
 155  * dtor --
 156  *      convert degrees to radians
 157  */
 158 double
 159 dtor(deg)
 160         double deg;
 161 {
 162         return(deg * PI / 180);
 163 }
 164
 165 /*
 166  * adj360 --
 167  *      adjust value so 0 <= deg <= 360
 168  */
 169 double
 170 adj360(deg)
 171         double *deg;
 172 {
 173         for (;;)
 174                 if (*deg < 0)
 175                         *deg += 360;
 176                 else if (*deg > 360)
 177                         *deg -= 360;
 178                 else
 179                         break;
 180 }