1 #include "astro.h"
2 
3 void
4 nutate(void)
5 {
6 
7 /*
8  *	uses radian, radsec
9  *	sets phi, eps, dphi, deps, obliq, gst, tobliq
10  */
11 
12 	double msun, mnom, noded, dmoon;
13 
14 /*
15  *	nutation of the equinoxes is a wobble of the pole
16  *	of the earths rotation whose magnitude is about
17  *	9 seconds of arc and whose period is about 18.6 years.
18  *
19  *	it depends upon the pull of the sun and moon on the
20  *	equatorial bulge of the earth.
21  *
22  *	phi and eps are the two angles which specify the
23  *	true pole with respect to the mean pole.
24  *
25  *	all coeffieients are from Exp. Supp. pp.44-45
26  */
27 
28 	mnom = 296.104608 + 13.0649924465*eday + 9.192e-3*capt2
29 		 + 14.38e-6*capt3;
30 	mnom *= radian;
31 	msun = 358.475833 + .9856002669*eday - .150e-3*capt2
32 		 - 3.33e-6*capt3;
33 	msun *= radian;
34 	noded = 11.250889 + 13.2293504490*eday - 3.211e-3*capt2
35 		 - 0.33e-6*capt3;
36 	noded *= radian;
37 	dmoon = 350.737486 + 12.1907491914*eday - 1.436e-3*capt2
38 		 + 1.89e-6*capt3;
39 	dmoon *= radian;
40 	node = 259.183275 - .0529539222*eday + 2.078e-3*capt2
41 		 + 2.22e-6*capt3;
42 	node *= radian;
43 
44 /*
45  *	long period terms
46  */
47 
48 	phi = 0.;
49 	eps = 0.;
50 	dphi = 0.;
51 	deps = 0.;
52 
53 
54 	icosadd(nutfp, nutcp);
55 	phi = -(17.2327+.01737*capt)*sin(node);
56 	phi += sinadd(4, node, noded, dmoon, msun);
57 
58 	eps = cosadd(4, node, noded, dmoon, msun);
59 
60 /*
61  *	short period terms
62  */
63 
64 
65 	dphi = sinadd(4, node, noded, mnom, dmoon);
66 
67 	deps = cosadd(3, node, noded, mnom);
68 
69 	phi = (phi+dphi)*radsec;
70 	eps = (eps+deps)*radsec;
71 	dphi *= radsec;
72 	deps *= radsec;
73 
74 	obliq = 23.452294 - .0130125*capt - 1.64e-6*capt2
75 		 + 0.503e-6*capt3;
76 	obliq *= radian;
77 	tobliq = obliq + eps;
78 
79 	gst = 99.690983 + 360.9856473354*eday + .000387*capt2;
80 	gst -= 180.;
81 	gst = fmod(gst, 360.);
82 	if(gst < 0.)
83 		gst += 360.;
84 	gst *= radian;
85 	gst += phi*cos(obliq);
86 }