pom.c revision 37868 
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. All advertising materials mentioning features or use of this software
16 *    must display the following acknowledgement:
17 *	This product includes software developed by the University of
18 *	California, Berkeley and its contributors.
19 * 4. Neither the name of the University nor the names of its contributors
20 *    may be used to endorse or promote products derived from this software
21 *    without specific prior written permission.
22 *
23 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
24 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
25 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
26 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
27 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
28 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
29 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
30 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
31 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
32 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
33 * SUCH DAMAGE.
34 */
35
36#ifndef lint
37static const char copyright[] =
38"@(#) Copyright (c) 1989, 1993\n\
39	The Regents of the University of California.  All rights reserved.\n";
40#endif /* not lint */
41
42#ifndef lint
43static const char sccsid[] = "@(#)pom.c       8.1 (Berkeley) 5/31/93";
44#endif /* not lint */
45
46/*
47 * Phase of the Moon.  Calculates the current phase of the moon.
48 * Based on routines from `Practical Astronomy with Your Calculator',
49 * by Duffett-Smith.  Comments give the section from the book that
50 * particular piece of code was adapted from.
51 *
52 * -- Keith E. Brandt  VIII 1984
53 *
54 */
55
56#include <time.h>
57#include <stdio.h>
58#include <math.h>
59
60#define	PI	  3.141592654
61#define	EPOCH	  85
62#define	EPSILONg  279.611371	/* solar ecliptic long at EPOCH */
63#define	RHOg	  282.680403	/* solar ecliptic long of perigee at EPOCH */
64#define	ECCEN	  0.01671542	/* solar orbit eccentricity */
65#define	lzero	  18.251907	/* lunar mean long at EPOCH */
66#define	Pzero	  192.917585	/* lunar mean long of perigee at EPOCH */
67#define	Nzero	  55.204723	/* lunar mean long of node at EPOCH */
68#define isleap(y) ((((y) % 4) == 0 && ((y) % 100) != 0) || ((y) % 400) == 0)
69
70static void	adj360 __P((double *));
71static double	dtor __P((double));
72static double	potm __P((double));
73
74int
75main()
76{
77	time_t tt;
78	struct tm *GMT;
79	double days, today, tomorrow;
80	int cnt;
81
82	(void) time(&tt);
83	GMT = gmtime(&tt);
84	days = (GMT->tm_yday + 1) + ((GMT->tm_hour +
85	    (GMT->tm_min / 60.0) + (GMT->tm_sec / 3600.0)) / 24.0);
86	for (cnt = EPOCH; cnt < GMT->tm_year; ++cnt)
87		days += isleap(1900 + cnt) ? 366 : 365;
88	today = potm(days) + .5;
89	(void)printf("The Moon is ");
90	if ((int)today == 100)
91		(void)printf("Full\n");
92	else if (!(int)today)
93		(void)printf("New\n");
94	else {
95		tomorrow = potm(days + 1);
96		if ((int)today == 50)
97			(void)printf("%s\n", tomorrow > today ?
98			    "at the First Quarter" : "at the Last Quarter");
99		else {
100			(void)printf("%s ", tomorrow > today ?
101			    "Waxing" : "Waning");
102			if (today > 50)
103				(void)printf("Gibbous (%1.0f%% of Full)\n",
104				    today);
105			else if (today < 50)
106				(void)printf("Crescent (%1.0f%% of Full)\n",
107				    today);
108		}
109	}
110
111	return 0;
112}
113
114/*
115 * potm --
116 *	return phase of the moon
117 */
118static double
119potm(days)
120	double days;
121{
122	double N, Msol, Ec, LambdaSol, l, Mm, Ev, Ac, A3, Mmprime;
123	double A4, lprime, V, ldprime, D, Nm;
124
125	N = 360 * days / 365.2422;				/* sec 42 #3 */
126	adj360(&N);
127	Msol = N + EPSILONg - RHOg;				/* sec 42 #4 */
128	adj360(&Msol);
129	Ec = 360 / PI * ECCEN * sin(dtor(Msol));		/* sec 42 #5 */
130	LambdaSol = N + Ec + EPSILONg;				/* sec 42 #6 */
131	adj360(&LambdaSol);
132	l = 13.1763966 * days + lzero;				/* sec 61 #4 */
133	adj360(&l);
134	Mm = l - (0.1114041 * days) - Pzero;			/* sec 61 #5 */
135	adj360(&Mm);
136	Nm = Nzero - (0.0529539 * days);			/* sec 61 #6 */
137	adj360(&Nm);
138	Ev = 1.2739 * sin(dtor(2*(l - LambdaSol) - Mm));	/* sec 61 #7 */
139	Ac = 0.1858 * sin(dtor(Msol));				/* sec 61 #8 */
140	A3 = 0.37 * sin(dtor(Msol));
141	Mmprime = Mm + Ev - Ac - A3;				/* sec 61 #9 */
142	Ec = 6.2886 * sin(dtor(Mmprime));			/* sec 61 #10 */
143	A4 = 0.214 * sin(dtor(2 * Mmprime));			/* sec 61 #11 */
144	lprime = l + Ev + Ec - Ac + A4;				/* sec 61 #12 */
145	V = 0.6583 * sin(dtor(2 * (lprime - LambdaSol)));	/* sec 61 #13 */
146	ldprime = lprime + V;					/* sec 61 #14 */
147	D = ldprime - LambdaSol;				/* sec 63 #2 */
148	return(50 * (1 - cos(dtor(D))));			/* sec 63 #3 */
149}
150
151/*
152 * dtor --
153 *	convert degrees to radians
154 */
155static double
156dtor(deg)
157	double deg;
158{
159	return(deg * PI / 180);
160}
161
162/*
163 * adj360 --
164 *	adjust value so 0 <= deg <= 360
165 */
166static void
167adj360(deg)
168	double *deg;
169{
170	for (;;)
171		if (*deg < 0)
172			*deg += 360;
173		else if (*deg > 360)
174			*deg -= 360;
175		else
176			break;
177}
178