pom/pom.c

   1 /*      $NetBSD: pom.c,v 1.8 1997/10/12 01:01:39 lukem 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 #include <sys/cdefs.h>
  39 #ifndef lint
  40 __COPYRIGHT("@(#) 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 __RCSID("$NetBSD: pom.c,v 1.8 1997/10/12 01:01:39 lukem 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 <err.h>
  64 #include <errno.h>
  65 #include <math.h>
  66 #include <stdio.h>
  67 #include <string.h>
  68 #include <tzfile.h>
  69
  70 #define PI        3.141592654
  71 #define EPOCH     85
  72 #define EPSILONg  279.611371    /* solar ecliptic long at EPOCH */
  73 #define RHOg      282.680403    /* solar ecliptic long of perigee at EPOCH */
  74 #define ECCEN     0.01671542    /* solar orbit eccentricity */
  75 #define lzero     18.251907     /* lunar mean long at EPOCH */
  76 #define Pzero     192.917585    /* lunar mean long of perigee at EPOCH */
  77 #define Nzero     55.204723     /* lunar mean long of node at EPOCH */
  78
  79 void    adj360 __P((double *));
  80 double  dtor __P((double));
  81 int     main __P((int, char *[]));
  82 double  potm __P((double));
  83
  84 int
  85 main(argc, argv)
  86         int argc;
  87         char *argv[];
  88 {
  89         struct timeval tp;
  90         struct timezone tzp;
  91         struct tm *GMT;
  92         time_t tmpt;
  93         double days, today, tomorrow;
  94         int cnt;
  95
  96         if (gettimeofday(&tp,&tzp))
  97                 err(1, "gettimeofday");
  98         tmpt = tp.tv_sec;
  99         GMT = gmtime(&tmpt);
 100         days = (GMT->tm_yday + 1) + ((GMT->tm_hour +
 101             (GMT->tm_min / 60.0) + (GMT->tm_sec / 3600.0)) / 24.0);
 102         for (cnt = EPOCH; cnt < GMT->tm_year; ++cnt)
 103                 days += isleap(cnt) ? 366 : 365;
 104         today = potm(days) + .5;
 105         (void)printf("The Moon is ");
 106         if ((int)today == 100)
 107                 (void)printf("Full\n");
 108         else if (!(int)today)
 109                 (void)printf("New\n");
 110         else {
 111                 tomorrow = potm(days + 1);
 112                 if ((int)today == 50)
 113                         (void)printf("%s\n", tomorrow > today ?
 114                             "at the First Quarter" : "at the Last Quarter");
 115                 else {
 116                         (void)printf("%s ", tomorrow > today ?
 117                             "Waxing" : "Waning");
 118                         if (today > 50)
 119                                 (void)printf("Gibbous (%1.0f%% of Full)\n",
 120                                     today);
 121                         else if (today < 50)
 122                                 (void)printf("Crescent (%1.0f%% of Full)\n",
 123                                     today);
 124                 }
 125         }
 126         exit(0);
 127 }
 128
 129 /*
 130  * potm --
 131  *      return phase of the moon
 132  */
 133 double
 134 potm(days)
 135         double days;
 136 {
 137         double N, Msol, Ec, LambdaSol, l, Mm, Ev, Ac, A3, Mmprime;
 138         double A4, lprime, V, ldprime, D, Nm;
 139
 140         N = 360 * days / 365.2422;                              /* sec 42 #3 */
 141         adj360(&N);
 142         Msol = N + EPSILONg - RHOg;                             /* sec 42 #4 */
 143         adj360(&Msol);
 144         Ec = 360 / PI * ECCEN * sin(dtor(Msol));                /* sec 42 #5 */
 145         LambdaSol = N + Ec + EPSILONg;                          /* sec 42 #6 */
 146         adj360(&LambdaSol);
 147         l = 13.1763966 * days + lzero;                          /* sec 61 #4 */
 148         adj360(&l);
 149         Mm = l - (0.1114041 * days) - Pzero;                    /* sec 61 #5 */
 150         adj360(&Mm);
 151         Nm = Nzero - (0.0529539 * days);                        /* sec 61 #6 */
 152         adj360(&Nm);
 153         Ev = 1.2739 * sin(dtor(2*(l - LambdaSol) - Mm));        /* sec 61 #7 */
 154         Ac = 0.1858 * sin(dtor(Msol));                          /* sec 61 #8 */
 155         A3 = 0.37 * sin(dtor(Msol));
 156         Mmprime = Mm + Ev - Ac - A3;                            /* sec 61 #9 */
 157         Ec = 6.2886 * sin(dtor(Mmprime));                       /* sec 61 #10 */
 158         A4 = 0.214 * sin(dtor(2 * Mmprime));                    /* sec 61 #11 */
 159         lprime = l + Ev + Ec - Ac + A4;                         /* sec 61 #12 */
 160         V = 0.6583 * sin(dtor(2 * (lprime - LambdaSol)));       /* sec 61 #13 */
 161         ldprime = lprime + V;                                   /* sec 61 #14 */
 162         D = ldprime - LambdaSol;                                /* sec 63 #2 */
 163         return(50 * (1 - cos(dtor(D))));                        /* sec 63 #3 */
 164 }
 165
 166 /*
 167  * dtor --
 168  *      convert degrees to radians
 169  */
 170 double
 171 dtor(deg)
 172         double deg;
 173 {
 174         return(deg * PI / 180);
 175 }
 176
 177 /*
 178  * adj360 --
 179  *      adjust value so 0 <= deg <= 360
 180  */
 181 void
 182 adj360(deg)
 183         double *deg;
 184 {
 185         for (;;)
 186                 if (*deg < 0)
 187                         *deg += 360;
 188                 else if (*deg > 360)
 189                         *deg -= 360;
 190                 else
 191                         break;
 192 }