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
main(void)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
potm(double days)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
dtor(double deg)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
adj360(double * deg)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