1 files changed, 86 insertions, 0 deletions
diff --git a/src/cmd/astro/nutate.c b/src/cmd/astro/nutate.c
new file mode 100644
index 00000000..bc7daa31
--- /dev/null
+++ b/src/cmd/astro/nutate.c
@@ -0,0 +1,86 @@
+#include "astro.h"
+
+void
+nutate(void)
+{
+
+/*
+ *	uses radian, radsec
+ *	sets phi, eps, dphi, deps, obliq, gst, tobliq
+ */
+
+	double msun, mnom, noded, dmoon;
+
+/*
+ *	nutation of the equinoxes is a wobble of the pole
+ *	of the earths rotation whose magnitude is about
+ *	9 seconds of arc and whose period is about 18.6 years.
+ *
+ *	it depends upon the pull of the sun and moon on the
+ *	equatorial bulge of the earth.
+ *
+ *	phi and eps are the two angles which specify the
+ *	true pole with respect to the mean pole.
+ *
+ *	all coeffieients are from Exp. Supp. pp.44-45
+ */
+
+	mnom = 296.104608 + 13.0649924465*eday + 9.192e-3*capt2
+		 + 14.38e-6*capt3;
+	mnom *= radian;
+	msun = 358.475833 + .9856002669*eday - .150e-3*capt2
+		 - 3.33e-6*capt3;
+	msun *= radian;
+	noded = 11.250889 + 13.2293504490*eday - 3.211e-3*capt2
+		 - 0.33e-6*capt3;
+	noded *= radian;
+	dmoon = 350.737486 + 12.1907491914*eday - 1.436e-3*capt2
+		 + 1.89e-6*capt3;
+	dmoon *= radian;
+	node = 259.183275 - .0529539222*eday + 2.078e-3*capt2
+		 + 2.22e-6*capt3;
+	node *= radian;
+
+/*
+ *	long period terms
+ */
+
+	phi = 0.;
+	eps = 0.;
+	dphi = 0.;
+	deps = 0.;
+
+
+	icosadd(nutfp, nutcp);
+	phi = -(17.2327+.01737*capt)*sin(node);
+	phi += sinadd(4, node, noded, dmoon, msun);
+
+	eps = cosadd(4, node, noded, dmoon, msun);
+
+/*
+ *	short period terms
+ */
+
+
+	dphi = sinadd(4, node, noded, mnom, dmoon);
+
+	deps = cosadd(3, node, noded, mnom);
+
+	phi = (phi+dphi)*radsec;
+	eps = (eps+deps)*radsec;
+	dphi *= radsec;
+	deps *= radsec;
+
+	obliq = 23.452294 - .0130125*capt - 1.64e-6*capt2
+		 + 0.503e-6*capt3;
+	obliq *= radian;
+	tobliq = obliq + eps;
+
+	gst = 99.690983 + 360.9856473354*eday + .000387*capt2;
+	gst -= 180.;
+	gst = fmod(gst, 360.);
+	if(gst < 0.)
+		gst += 360.;
+	gst *= radian;
+	gst += phi*cos(obliq);
+}