1 /* 2 * Copyright (c) 1989 The Regents of the University of California. 3 * All rights reserved. 4 * 5 * This code is derived from software posted to USENET. 6 * 7 * %sccs.include.redist.c% 8 */ 9 10 #ifndef lint 11 char copyright[] = 12 "@(#) Copyright (c) 1989 The Regents of the University of California.\n\ 13 All rights reserved.\n"; 14 #endif /* not lint */ 15 16 #ifndef lint 17 static char sccsid[] = "@(#)pom.c 5.3 (Berkeley) 02/28/91"; 18 #endif /* not lint */ 19 20 /* 21 * Phase of the Moon. Calculates the current phase of the moon. 22 * Based on routines from `Practical Astronomy with Your Calculator', 23 * by Duffett-Smith. Comments give the section from the book that 24 * particular piece of code was adapted from. 25 * 26 * -- Keith E. Brandt VIII 1984 27 * 28 */ 29 30 #include <sys/time.h> 31 #include <stdio.h> 32 #include <tzfile.h> 33 #include <math.h> 34 35 #define PI 3.141592654 36 #define EPOCH 85 37 #define EPSILONg 279.611371 /* solar ecliptic long at EPOCH */ 38 #define RHOg 282.680403 /* solar ecliptic long of perigee at EPOCH */ 39 #define ECCEN 0.01671542 /* solar orbit eccentricity */ 40 #define lzero 18.251907 /* lunar mean long at EPOCH */ 41 #define Pzero 192.917585 /* lunar mean long of perigee at EPOCH */ 42 #define Nzero 55.204723 /* lunar mean long of node at EPOCH */ 43 44 double dtor(), potm(), adj360(); 45 46 main() 47 { 48 extern int errno; 49 struct timeval tp; 50 struct timezone tzp; 51 struct tm *GMT, *gmtime(); 52 double days, today, tomorrow; 53 int cnt; 54 char *strerror(); 55 56 if (gettimeofday(&tp,&tzp)) { 57 (void)fprintf(stderr, "pom: %s\n", strerror(errno)); 58 exit(1); 59 } 60 GMT = gmtime(&tp.tv_sec); 61 days = (GMT->tm_yday + 1) + ((GMT->tm_hour + 62 (GMT->tm_min / 60.0) + (GMT->tm_sec / 3600.0)) / 24.0); 63 for (cnt = EPOCH; cnt < GMT->tm_year; ++cnt) 64 days += isleap(cnt) ? 366 : 365; 65 today = potm(days) + .5; 66 (void)printf("The Moon is "); 67 if ((int)today == 100) 68 (void)printf("Full\n"); 69 else if (!(int)today) 70 (void)printf("New\n"); 71 else { 72 tomorrow = potm(days + 1); 73 if ((int)today == 50) 74 (void)printf("%s\n", tomorrow > today ? 75 "at the First Quarter" : "at the Last Quarter"); 76 else { 77 (void)printf("%s ", tomorrow > today ? 78 "Waxing" : "Waning"); 79 if (today > 50) 80 (void)printf("Gibbous (%1.0f%% of Full)\n", 81 today); 82 else if (today < 50) 83 (void)printf("Crescent (%1.0f%% of Full)\n", 84 today); 85 } 86 } 87 } 88 89 /* 90 * potm -- 91 * return phase of the moon 92 */ 93 double 94 potm(days) 95 double days; 96 { 97 double N, Msol, Ec, LambdaSol, l, Mm, Ev, Ac, A3, Mmprime; 98 double A4, lprime, V, ldprime, D, Nm; 99 100 N = 360 * days / 365.2422; /* sec 42 #3 */ 101 adj360(&N); 102 Msol = N + EPSILONg - RHOg; /* sec 42 #4 */ 103 adj360(&Msol); 104 Ec = 360 / PI * ECCEN * sin(dtor(Msol)); /* sec 42 #5 */ 105 LambdaSol = N + Ec + EPSILONg; /* sec 42 #6 */ 106 adj360(&LambdaSol); 107 l = 13.1763966 * days + lzero; /* sec 61 #4 */ 108 adj360(&l); 109 Mm = l - (0.1114041 * days) - Pzero; /* sec 61 #5 */ 110 adj360(&Mm); 111 Nm = Nzero - (0.0529539 * days); /* sec 61 #6 */ 112 adj360(&Nm); 113 Ev = 1.2739 * sin(dtor(2*(l - LambdaSol) - Mm)); /* sec 61 #7 */ 114 Ac = 0.1858 * sin(dtor(Msol)); /* sec 61 #8 */ 115 A3 = 0.37 * sin(dtor(Msol)); 116 Mmprime = Mm + Ev - Ac - A3; /* sec 61 #9 */ 117 Ec = 6.2886 * sin(dtor(Mmprime)); /* sec 61 #10 */ 118 A4 = 0.214 * sin(dtor(2 * Mmprime)); /* sec 61 #11 */ 119 lprime = l + Ev + Ec - Ac + A4; /* sec 61 #12 */ 120 V = 0.6583 * sin(dtor(2 * (lprime - LambdaSol))); /* sec 61 #13 */ 121 ldprime = lprime + V; /* sec 61 #14 */ 122 D = ldprime - LambdaSol; /* sec 63 #2 */ 123 return(50 * (1 - cos(dtor(D)))); /* sec 63 #3 */ 124 } 125 126 /* 127 * dtor -- 128 * convert degrees to radians 129 */ 130 double 131 dtor(deg) 132 double deg; 133 { 134 return(deg * PI / 180); 135 } 136 137 /* 138 * adj360 -- 139 * adjust value so 0 <= deg <= 360 140 */ 141 double 142 adj360(deg) 143 double *deg; 144 { 145 for (;;) 146 if (*deg < 0) 147 *deg += 360; 148 else if (*deg > 360) 149 *deg -= 360; 150 else 151 break; 152 } 153