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. 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  * @(#) Copyright (c) 1989, 1993 The Regents of the University of California.  All rights reserved.
  36  * @(#)pom.c       8.1 (Berkeley) 5/31/93
  37  * $FreeBSD: src/games/pom/pom.c,v 1.9 1999/11/30 03:49:09 billf Exp $
  38  * $DragonFly: src/games/pom/pom.c,v 1.4 2006/08/08 17:08:49 pavalos Exp $
  39  */
  40
  41 /*
  42  * Phase of the Moon.  Calculates the current phase of the moon.
  43  * Based on routines from `Practical Astronomy with Your Calculator',
  44  * by Duffett-Smith.  Comments give the section from the book that
  45  * particular piece of code was adapted from.
  46  *
  47  * -- Keith E. Brandt  VIII 1984
  48  *
  49  */
  50
  51 #include <time.h>
  52 #include <stdio.h>
  53 #include <math.h>
  54
  55 #define EPOCH     85
  56 #define EPSILONg  279.611371    /* solar ecliptic long at EPOCH */
  57 #define RHOg      282.680403    /* solar ecliptic long of perigee at EPOCH */
  58 #define ECCEN     0.01671542    /* solar orbit eccentricity */
  59 #define lzero     18.251907     /* lunar mean long at EPOCH */
  60 #define Pzero     192.917585    /* lunar mean long of perigee at EPOCH */
  61 #define Nzero     55.204723     /* lunar mean long of node at EPOCH */
  62 #define isleap(y) ((((y) % 4) == 0 && ((y) % 100) != 0) || ((y) % 400) == 0)
  63
  64 static void     adj360 (double *);
  65 static double   dtor (double);
  66 static double   potm (double);
  67
  68 int
  69 main(void)
  70 {
  71         time_t tt;
  72         struct tm *GMT;
  73         double days, today, tomorrow;
  74         int cnt;
  75
  76         (void) time(&tt);
  77         GMT = gmtime(&tt);
  78         days = (GMT->tm_yday + 1) + ((GMT->tm_hour +
  79             (GMT->tm_min / 60.0) + (GMT->tm_sec / 3600.0)) / 24.0);
  80         for (cnt = EPOCH; cnt < GMT->tm_year; ++cnt)
  81                 days += isleap(1900 + cnt) ? 366 : 365;
  82         today = potm(days) + .5;
  83         (void)printf("The Moon is ");
  84         if ((int)today == 100)
  85                 (void)printf("Full\n");
  86         else if (!(int)today)
  87                 (void)printf("New\n");
  88         else {
  89                 tomorrow = potm(days + 1);
  90                 if ((int)today == 50)
  91                         (void)printf("%s\n", tomorrow > today ?
  92                             "at the First Quarter" : "at the Last Quarter");
  93                 else {
  94                         (void)printf("%s ", tomorrow > today ?
  95                             "Waxing" : "Waning");
  96                         if (today > 50)
  97                                 (void)printf("Gibbous (%1.0f%% of Full)\n",
  98                                     today);
  99                         else if (today < 50)
 100                                 (void)printf("Crescent (%1.0f%% of Full)\n",
 101                                     today);
 102                 }
 103         }
 104
 105         return 0;
 106 }
 107
 108 /*
 109  * potm --
 110  *      return phase of the moon
 111  */
 112 static double
 113 potm(double days)
 114 {
 115         double N, Msol, Ec, LambdaSol, l, Mm, Ev, Ac, A3, Mmprime;
 116         double A4, lprime, V, ldprime, D, Nm;
 117
 118         N = 360 * days / 365.2422;                              /* sec 42 #3 */
 119         adj360(&N);
 120         Msol = N + EPSILONg - RHOg;                             /* sec 42 #4 */
 121         adj360(&Msol);
 122         Ec = 360 / M_PI * ECCEN * sin(dtor(Msol));              /* sec 42 #5 */
 123         LambdaSol = N + Ec + EPSILONg;                          /* sec 42 #6 */
 124         adj360(&LambdaSol);
 125         l = 13.1763966 * days + lzero;                          /* sec 61 #4 */
 126         adj360(&l);
 127         Mm = l - (0.1114041 * days) - Pzero;                    /* sec 61 #5 */
 128         adj360(&Mm);
 129         Nm = Nzero - (0.0529539 * days);                        /* sec 61 #6 */
 130         adj360(&Nm);
 131         Ev = 1.2739 * sin(dtor(2*(l - LambdaSol) - Mm));        /* sec 61 #7 */
 132         Ac = 0.1858 * sin(dtor(Msol));                          /* sec 61 #8 */
 133         A3 = 0.37 * sin(dtor(Msol));
 134         Mmprime = Mm + Ev - Ac - A3;                            /* sec 61 #9 */
 135         Ec = 6.2886 * sin(dtor(Mmprime));                       /* sec 61 #10 */
 136         A4 = 0.214 * sin(dtor(2 * Mmprime));                    /* sec 61 #11 */
 137         lprime = l + Ev + Ec - Ac + A4;                         /* sec 61 #12 */
 138         V = 0.6583 * sin(dtor(2 * (lprime - LambdaSol)));       /* sec 61 #13 */
 139         ldprime = lprime + V;                                   /* sec 61 #14 */
 140         D = ldprime - LambdaSol;                                /* sec 63 #2 */
 141         return(50 * (1 - cos(dtor(D))));                        /* sec 63 #3 */
 142 }
 143
 144 /*
 145  * dtor --
 146  *      convert degrees to radians
 147  */
 148 static double
 149 dtor(double deg)
 150 {
 151         return(deg * M_PI / 180);
 152 }
 153
 154 /*
 155  * adj360 --
 156  *      adjust value so 0 <= deg <= 360
 157  */
 158 static void
 159 adj360(double *deg)
 160 {
 161         for (;;)
 162                 if (*deg < 0)
 163                         *deg += 360;
 164                 else if (*deg > 360)
 165                         *deg -= 360;
 166                 else
 167                         break;
 168 }