games/pom/pom.c

   1 /*-
   2  * Copyright (c) 1989, 1993
   3  *      The Regents of the University of California.  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. Neither the name of the University nor the names of its contributors
  16  *    may be used to endorse or promote products derived from this software
  17  *    without specific prior written permission.
  18  *
  19  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  20  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  21  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  22  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  23  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  24  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  25  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  26  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  27  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  28  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  29  * SUCH DAMAGE.
  30  *
  31  * @(#) Copyright (c) 1989, 1993 The Regents of the University of California.  All rights reserved.
  32  * @(#)pom.c       8.1 (Berkeley) 5/31/93
  33  * $FreeBSD: src/games/pom/pom.c,v 1.9 1999/11/30 03:49:09 billf Exp $
  34  * $DragonFly: src/games/pom/pom.c,v 1.4 2006/08/08 17:08:49 pavalos Exp $
  35  */
  36
  37 /*
  38  * Phase of the Moon.  Calculates the current phase of the moon.
  39  * Based on routines from `Practical Astronomy with Your Calculator',
  40  * by Duffett-Smith.  Comments give the section from the book that
  41  * particular piece of code was adapted from.
  42  *
  43  * -- Keith E. Brandt  VIII 1984
  44  *
  45  */
  46
  47 #include <time.h>
  48 #include <stdio.h>
  49 #include <math.h>
  50
  51 #define EPOCH     85
  52 #define EPSILONg  279.611371    /* solar ecliptic long at EPOCH */
  53 #define RHOg      282.680403    /* solar ecliptic long of perigee at EPOCH */
  54 #define ECCEN     0.01671542    /* solar orbit eccentricity */
  55 #define lzero     18.251907     /* lunar mean long at EPOCH */
  56 #define Pzero     192.917585    /* lunar mean long of perigee at EPOCH */
  57 #define Nzero     55.204723     /* lunar mean long of node at EPOCH */
  58 #define isleap(y) ((((y) % 4) == 0 && ((y) % 100) != 0) || ((y) % 400) == 0)
  59
  60 static void     adj360 (double *);
  61 static double   dtor (double);
  62 static double   potm (double);
  63
  64 int
  65 main(void)
  66 {
  67         time_t tt;
  68         struct tm *GMT;
  69         double days, today, tomorrow;
  70         int cnt;
  71
  72         (void) time(&tt);
  73         GMT = gmtime(&tt);
  74         days = (GMT->tm_yday + 1) + ((GMT->tm_hour +
  75             (GMT->tm_min / 60.0) + (GMT->tm_sec / 3600.0)) / 24.0);
  76         for (cnt = EPOCH; cnt < GMT->tm_year; ++cnt)
  77                 days += isleap(1900 + cnt) ? 366 : 365;
  78         today = potm(days) + .5;
  79         (void)printf("The Moon is ");
  80         if ((int)today == 100)
  81                 (void)printf("Full\n");
  82         else if (!(int)today)
  83                 (void)printf("New\n");
  84         else {
  85                 tomorrow = potm(days + 1);
  86                 if ((int)today == 50)
  87                         (void)printf("%s\n", tomorrow > today ?
  88                             "at the First Quarter" : "at the Last Quarter");
  89                 else {
  90                         (void)printf("%s ", tomorrow > today ?
  91                             "Waxing" : "Waning");
  92                         if (today > 50)
  93                                 (void)printf("Gibbous (%1.0f%% of Full)\n",
  94                                     today);
  95                         else if (today < 50)
  96                                 (void)printf("Crescent (%1.0f%% of Full)\n",
  97                                     today);
  98                 }
  99         }
 100
 101         return 0;
 102 }
 103
 104 /*
 105  * potm --
 106  *      return phase of the moon
 107  */
 108 static double
 109 potm(double days)
 110 {
 111         double N, Msol, Ec, LambdaSol, l, Mm, Ev, Ac, A3, Mmprime;
 112         double A4, lprime, V, ldprime, D, Nm;
 113
 114         N = 360 * days / 365.2422;                              /* sec 42 #3 */
 115         adj360(&N);
 116         Msol = N + EPSILONg - RHOg;                             /* sec 42 #4 */
 117         adj360(&Msol);
 118         Ec = 360 / M_PI * ECCEN * sin(dtor(Msol));              /* sec 42 #5 */
 119         LambdaSol = N + Ec + EPSILONg;                          /* sec 42 #6 */
 120         adj360(&LambdaSol);
 121         l = 13.1763966 * days + lzero;                          /* sec 61 #4 */
 122         adj360(&l);
 123         Mm = l - (0.1114041 * days) - Pzero;                    /* sec 61 #5 */
 124         adj360(&Mm);
 125         Nm = Nzero - (0.0529539 * days);                        /* sec 61 #6 */
 126         adj360(&Nm);
 127         Ev = 1.2739 * sin(dtor(2*(l - LambdaSol) - Mm));        /* sec 61 #7 */
 128         Ac = 0.1858 * sin(dtor(Msol));                          /* sec 61 #8 */
 129         A3 = 0.37 * sin(dtor(Msol));
 130         Mmprime = Mm + Ev - Ac - A3;                            /* sec 61 #9 */
 131         Ec = 6.2886 * sin(dtor(Mmprime));                       /* sec 61 #10 */
 132         A4 = 0.214 * sin(dtor(2 * Mmprime));                    /* sec 61 #11 */
 133         lprime = l + Ev + Ec - Ac + A4;                         /* sec 61 #12 */
 134         V = 0.6583 * sin(dtor(2 * (lprime - LambdaSol)));       /* sec 61 #13 */
 135         ldprime = lprime + V;                                   /* sec 61 #14 */
 136         D = ldprime - LambdaSol;                                /* sec 63 #2 */
 137         return(50 * (1 - cos(dtor(D))));                        /* sec 63 #3 */
 138 }
 139
 140 /*
 141  * dtor --
 142  *      convert degrees to radians
 143  */
 144 static double
 145 dtor(double deg)
 146 {
 147         return(deg * M_PI / 180);
 148 }
 149
 150 /*
 151  * adj360 --
 152  *      adjust value so 0 <= deg <= 360
 153  */
 154 static void
 155 adj360(double *deg)
 156 {
 157         for (;;)
 158                 if (*deg < 0)
 159                         *deg += 360;
 160                 else if (*deg > 360)
 161                         *deg -= 360;
 162                 else
 163                         break;
 164 }