usr/src/games/pom/pom.c

/*
 * Copyright (c) 1989 The Regents of the University of California.
 * All rights reserved.
 *
 * This code is derived from software posted to USENET.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#ifndef lint
char copyright[] =
"@(#) Copyright (c) 1989 The Regents of the University of California.\n\
 All rights reserved.\n";
#endif /* not lint */

#ifndef lint
static char sccsid[] = "@(#)pom.c       5.3 (Berkeley) 2/28/91";
#endif /* not lint */

/*
 * Phase of the Moon.  Calculates the current phase of the moon.
 * Based on routines from `Practical Astronomy with Your Calculator',
 * by Duffett-Smith.  Comments give the section from the book that
 * particular piece of code was adapted from.
 *
 * -- Keith E. Brandt  VIII 1984
 *
 */

#include <sys/time.h>
#include <stdio.h>
#include <tzfile.h>
#include <math.h>

#define PI        3.141592654
#define EPOCH     85
#define EPSILONg  279.611371    /* solar ecliptic long at EPOCH */
#define RHOg      282.680403    /* solar ecliptic long of perigee at EPOCH */
#define ECCEN     0.01671542    /* solar orbit eccentricity */
#define lzero     18.251907     /* lunar mean long at EPOCH */
#define Pzero     192.917585    /* lunar mean long of perigee at EPOCH */
#define Nzero     55.204723     /* lunar mean long of node at EPOCH */

double dtor(), potm(), adj360();

main()
{
        extern int errno;
        struct timeval tp;
        struct timezone tzp;
        struct tm *GMT, *gmtime();
        double days, today, tomorrow;
        int cnt;
        char *strerror();

        if (gettimeofday(&tp,&tzp)) {
                (void)fprintf(stderr, "pom: %s\n", strerror(errno));
                exit(1);
        }
        GMT = gmtime(&tp.tv_sec);
        days = (GMT->tm_yday + 1) + ((GMT->tm_hour +
            (GMT->tm_min / 60.0) + (GMT->tm_sec / 3600.0)) / 24.0);
        for (cnt = EPOCH; cnt < GMT->tm_year; ++cnt)
                days += isleap(cnt) ? 366 : 365;
        today = potm(days) + .5;
        (void)printf("The Moon is ");
        if ((int)today == 100)
                (void)printf("Full\n");
        else if (!(int)today)
                (void)printf("New\n");
        else {
                tomorrow = potm(days + 1);
                if ((int)today == 50)
                        (void)printf("%s\n", tomorrow > today ?
                            "at the First Quarter" : "at the Last Quarter");
                else {
                        (void)printf("%s ", tomorrow > today ?
                            "Waxing" : "Waning");
                        if (today > 50)
                                (void)printf("Gibbous (%1.0f%% of Full)\n",
                                    today);
                        else if (today < 50)
                                (void)printf("Crescent (%1.0f%% of Full)\n",
                                    today);
                }
        }
}

/*
 * potm --
 *      return phase of the moon
 */
double
potm(days)
        double days;
{
        double N, Msol, Ec, LambdaSol, l, Mm, Ev, Ac, A3, Mmprime;
        double A4, lprime, V, ldprime, D, Nm;

        N = 360 * days / 365.2422;                              /* sec 42 #3 */
        adj360(&N);
        Msol = N + EPSILONg - RHOg;                             /* sec 42 #4 */
        adj360(&Msol);
        Ec = 360 / PI * ECCEN * sin(dtor(Msol));                /* sec 42 #5 */
        LambdaSol = N + Ec + EPSILONg;                          /* sec 42 #6 */
        adj360(&LambdaSol);
        l = 13.1763966 * days + lzero;                          /* sec 61 #4 */
        adj360(&l);
        Mm = l - (0.1114041 * days) - Pzero;                    /* sec 61 #5 */
        adj360(&Mm);
        Nm = Nzero - (0.0529539 * days);                        /* sec 61 #6 */
        adj360(&Nm);
        Ev = 1.2739 * sin(dtor(2*(l - LambdaSol) - Mm));        /* sec 61 #7 */
        Ac = 0.1858 * sin(dtor(Msol));                          /* sec 61 #8 */
        A3 = 0.37 * sin(dtor(Msol));
        Mmprime = Mm + Ev - Ac - A3;                            /* sec 61 #9 */
        Ec = 6.2886 * sin(dtor(Mmprime));                       /* sec 61 #10 */
        A4 = 0.214 * sin(dtor(2 * Mmprime));                    /* sec 61 #11 */
        lprime = l + Ev + Ec - Ac + A4;                         /* sec 61 #12 */
        V = 0.6583 * sin(dtor(2 * (lprime - LambdaSol)));       /* sec 61 #13 */
        ldprime = lprime + V;                                   /* sec 61 #14 */
        D = ldprime - LambdaSol;                                /* sec 63 #2 */
        return(50 * (1 - cos(dtor(D))));                        /* sec 63 #3 */
}

/*
 * dtor --
 *      convert degrees to radians
 */
double
dtor(deg)
        double deg;
{
        return(deg * PI / 180);
}

/*
 * adj360 --
 *      adjust value so 0 <= deg <= 360
 */
double
adj360(deg)
        double *deg;
{
        for (;;)
                if (*deg < 0)
                        *deg += 360;
                else if (*deg > 360)
                        *deg -= 360;
                else
                        break;
}