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 */ 35 36 /* 37 * Phase of the Moon. Calculates the current phase of the moon. 38 * Based on routines from `Practical Astronomy with Your Calculator', 39 * by Duffett-Smith. Comments give the section from the book that 40 * particular piece of code was adapted from. 41 * 42 * -- Keith E. Brandt VIII 1984 43 * 44 */ 45 46 #include <time.h> 47 #include <stdio.h> 48 #include <math.h> 49 50 #define EPOCH 85 51 #define EPSILONg 279.611371 /* solar ecliptic long at EPOCH */ 52 #define RHOg 282.680403 /* solar ecliptic long of perigee at EPOCH */ 53 #define ECCEN 0.01671542 /* solar orbit eccentricity */ 54 #define lzero 18.251907 /* lunar mean long at EPOCH */ 55 #define Pzero 192.917585 /* lunar mean long of perigee at EPOCH */ 56 #define Nzero 55.204723 /* lunar mean long of node at EPOCH */ 57 #define isleap(y) ((((y) % 4) == 0 && ((y) % 100) != 0) || ((y) % 400) == 0) 58 59 static void adj360 (double *); 60 static double dtor (double); 61 static double potm (double); 62 63 int 64 main(void) 65 { 66 time_t tt; 67 struct tm *GMT; 68 double days, today, tomorrow; 69 int cnt; 70 71 time(&tt); 72 GMT = gmtime(&tt); 73 days = (GMT->tm_yday + 1) + ((GMT->tm_hour + 74 (GMT->tm_min / 60.0) + (GMT->tm_sec / 3600.0)) / 24.0); 75 for (cnt = EPOCH; cnt < GMT->tm_year; ++cnt) 76 days += isleap(1900 + cnt) ? 366 : 365; 77 today = potm(days) + .5; 78 printf("The Moon is "); 79 if ((int)today == 100) 80 printf("Full\n"); 81 else if (!(int)today) 82 printf("New\n"); 83 else { 84 tomorrow = potm(days + 1); 85 if ((int)today == 50) 86 printf("%s\n", tomorrow > today ? 87 "at the First Quarter" : "at the Last Quarter"); 88 else { 89 printf("%s ", tomorrow > today ? 90 "Waxing" : "Waning"); 91 if (today > 50) 92 printf("Gibbous (%1.0f%% of Full)\n", today); 93 else if (today < 50) 94 printf("Crescent (%1.0f%% of Full)\n", today); 95 } 96 } 97 98 return 0; 99 } 100 101 /* 102 * potm -- 103 * return phase of the moon 104 */ 105 static double 106 potm(double days) 107 { 108 double N, Msol, Ec, LambdaSol, l, Mm, Ev, Ac, A3, Mmprime; 109 double A4, lprime, V, ldprime, D, Nm; 110 111 N = 360 * days / 365.2422; /* sec 42 #3 */ 112 adj360(&N); 113 Msol = N + EPSILONg - RHOg; /* sec 42 #4 */ 114 adj360(&Msol); 115 Ec = 360 / M_PI * ECCEN * sin(dtor(Msol)); /* sec 42 #5 */ 116 LambdaSol = N + Ec + EPSILONg; /* sec 42 #6 */ 117 adj360(&LambdaSol); 118 l = 13.1763966 * days + lzero; /* sec 61 #4 */ 119 adj360(&l); 120 Mm = l - (0.1114041 * days) - Pzero; /* sec 61 #5 */ 121 adj360(&Mm); 122 Nm = Nzero - (0.0529539 * days); /* sec 61 #6 */ 123 adj360(&Nm); 124 Ev = 1.2739 * sin(dtor(2*(l - LambdaSol) - Mm)); /* sec 61 #7 */ 125 Ac = 0.1858 * sin(dtor(Msol)); /* sec 61 #8 */ 126 A3 = 0.37 * sin(dtor(Msol)); 127 Mmprime = Mm + Ev - Ac - A3; /* sec 61 #9 */ 128 Ec = 6.2886 * sin(dtor(Mmprime)); /* sec 61 #10 */ 129 A4 = 0.214 * sin(dtor(2 * Mmprime)); /* sec 61 #11 */ 130 lprime = l + Ev + Ec - Ac + A4; /* sec 61 #12 */ 131 V = 0.6583 * sin(dtor(2 * (lprime - LambdaSol))); /* sec 61 #13 */ 132 ldprime = lprime + V; /* sec 61 #14 */ 133 D = ldprime - LambdaSol; /* sec 63 #2 */ 134 return(50 * (1 - cos(dtor(D)))); /* sec 63 #3 */ 135 } 136 137 /* 138 * dtor -- 139 * convert degrees to radians 140 */ 141 static double 142 dtor(double deg) 143 { 144 return(deg * M_PI / 180); 145 } 146 147 /* 148 * adj360 -- 149 * adjust value so 0 <= deg <= 360 150 */ 151 static void 152 adj360(double *deg) 153 { 154 for (;;) 155 if (*deg < 0) 156 *deg += 360; 157 else if (*deg > 360) 158 *deg -= 360; 159 else 160 break; 161 } 162