diff --git a/src/sun.c b/src/sun.c
new file mode 100644
index 0000000..5876b26
--- /dev/null
+++ b/src/sun.c
@@ -0,0 +1,159 @@
+/**
+ * Calculation routines
+ *
+ * @copyright	2012 Steffen Vogel
+ * @license	http://www.gnu.org/licenses/gpl.txt GNU Public License
+ * @author	Steffen Vogel <post@steffenvogel.de>
+ * @link	http://www.steffenvogel.de/2012/03/14/cron-jobs-fur-sonnenauf-untergang/
+ */
+/*
+ * This file is part of sun
+ *
+ * sun is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * any later version.
+ *
+ * sun is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with sun. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <math.h>
+#include <stdio.h>
+
+#include "sun.h"
+
+double deg2rad(double deg) {
+	return M_PI * deg / 180.0;
+}
+
+double rad2deg(double rad) {
+	return 180 * rad / M_PI;
+}
+
+int julian_date(struct tm date) {
+	int year = date.tm_year + 1900;
+	int month = date.tm_mon + 1;
+	int day = date.tm_mday;
+
+	int a = (14 - month) / 12;
+	int y = year + 4800 - a;
+	int m = month + 12 * a - 3;
+	int jdn = day + (153 * m + 2) / 5 + 365 * y + y / 4 - y / 100 + y / 400 - 32045;
+
+	return jdn;
+}
+
+double in_pi(double x) {
+	x -= floor(x / M_2PI) * M_2PI;
+
+	return (x < 0) ? x + M_2PI : x;
+}
+
+double sun_eps(double days) {
+	double poly;
+
+	poly = -46.8150 * days - 0.00059 * powf(days, 2) + 0.001813 * powf(days, 3);
+	poly /= 3600.0;
+
+	return deg2rad(23.43929111 + poly);
+}
+
+double sun_eof(double days, double ra) {
+	double ra_mean = 18.71506921 + 2400.0513369 * days + (2.5862e-5 - 1.72e-9 * days) * powf(days, 2);
+	ra_mean = 24.0 * in_pi(M_2PI * ra_mean / 24.0) / M_2PI;
+	double ra_diff = ra_mean - ra;
+
+	if (ra_diff < -12) ra_diff += 24;
+	if (ra_diff > 12) ra_diff -= 24;
+
+	ra_diff *= 1.0027379;
+
+#ifdef DEBUG
+	printf("ra_mean = %.20f\n", ra_mean);
+	printf("ra_diff = %.20f\n", ra_diff);
+#endif
+
+	return ra_diff;
+}
+
+struct sun_coords sun_pos(double days) {
+	double m  = in_pi(M_2PI * (0.993133 + 99.997361 * days)); 
+	double l  = in_pi(M_2PI * (0.7859453 + m / M_2PI  + (6893 * sin(m) + 72.0 * sin(2 * m) + 6191.2 * days) / 1296.0e3));
+	double e = sun_eps(days);
+	double ra =  atan(tan(l)*cos(e));
+	double dk = asin(sin(e) * sin(l));
+
+	if (ra < 0) ra += M_PI;
+	if (l > M_PI) ra += M_PI;
+
+	ra *= 12 / M_PI;
+
+#ifdef DEBUG
+	printf("m = %.20f\n", m);
+	printf("l = %.20f\n", l);
+	printf("e = %.20f\n", e);
+	printf("dk = %.20f\n", dk);
+	printf("ra = %.20f\n", ra);
+#endif
+
+	struct sun_coords spos = { dk, ra };
+	return spos;
+}
+
+struct tm sun(struct coords pos, struct tm date, enum mode mode, double twilight, int timezone) {
+	/* calculate sun position */
+	double jd = julian_date(date);
+	double days = (jd - 2451545) / 36525;
+	struct sun_coords spos = sun_pos(days);
+
+	/* use equation of time */
+	double h = deg2rad(twilight);
+	double time = sun_eof(days, spos.ra);
+	double time_diff = 12.0 * acos((sin(h) - sin(deg2rad(pos.lat)) * sin(spos.dk)) / (cos(deg2rad(pos.lat)) * cos(spos.dk))) / M_PI;
+
+#ifdef DEBUG
+	printf("jd = %.20f\n", jd);
+	printf("days = %.20f\n", days);
+	printf("delta_days = %.20f\n", jd - 2451545);
+	printf("h = %.20f\n", h);
+	printf("time = %.20f\n", time);
+	printf("time_diff = %.20f\n", time_diff);
+#endif
+
+	double local = 12 - time;
+	double global = local - pos.lon / 15 + timezone;
+
+	switch (mode) {
+		case NOON: /* do nothing */ break;
+		case RISE:	global -= time_diff; break;
+		case SET:	global += time_diff; break;
+		case DAYTIME:	global = 2 * time_diff; break;
+		case NIGHTTIME:	global = 24 - 2 * time_diff; break;
+	}
+
+
+	if (global < 0) {
+		global += 24;
+	}
+	else if (global >= 24) {
+		global -= 24;
+	}
+
+#ifdef DEBUG
+	printf("local = %f\n", local);
+	printf("global = %f\n", global);
+#endif
+
+	date.tm_hour = (int) global;
+	date.tm_min = 60 * (global - date.tm_hour) + 0.5; /* math rounding */
+	date.tm_sec = 0; /* below our accuracy */
+	//date.tm_sec = 3600 * (global - date.tm_hour - date.tm_min / 60.0);
+
+	return date;
+}
diff --git a/src/sun.h b/src/sun.h
new file mode 100644
index 0000000..36132dd
--- /dev/null
+++ b/src/sun.h
@@ -0,0 +1,55 @@
+/**
+ * Header file for calculation
+ *
+ * @copyright	2012 Steffen Vogel
+ * @license	http://www.gnu.org/licenses/gpl.txt GNU Public License
+ * @author	Steffen Vogel <post@steffenvogel.de>
+ * @link	http://www.steffenvogel.de/2012/03/14/cron-jobs-fur-sonnenauf-untergang/
+ */
+/*
+ * This file is part of sun
+ *
+ * sun is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * any later version.
+ *
+ * sun is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with sun. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+
+#include <time.h>
+
+#ifdef GEONAMES_SUPPORT
+#include "geonames.h"
+#else
+struct coords { double lat, lon; };
+#endif
+
+struct sun_coords { double dk, ra; };
+
+//#define DEBUG 1
+#define GEONAMES_SUPPORT 1
+#define M_2PI (M_PI * 2)
+
+enum mode { RISE, SET, NOON, DAYTIME, NIGHTTIME };
+
+/* helper function */
+void usage();
+double deg2rad(double deg);
+double rad2deg(double rad);
+double in_pi(double x);
+int julian_date(struct tm date);
+
+/* calculation functions */
+struct tm sun(struct coords pos, struct tm date, enum mode mode, double twilight, int timezone);
+struct sun_coords sun_pos(double days);
+double sun_eof(double days, double ra);
+double sun_eps(double days);
+
diff --git a/src/sun_main.c b/src/sun_main.c
new file mode 100644
index 0000000..6f39a36
--- /dev/null
+++ b/src/sun_main.c
@@ -0,0 +1,286 @@
+/**
+ * Main routine
+ *
+ * Does parsing of command line options and start calculation
+ *
+ * @copyright	2012 Steffen Vogel
+ * @license	http://www.gnu.org/licenses/gpl.txt GNU Public License
+ * @author	Steffen Vogel <post@steffenvogel.de>
+ * @link	http://www.steffenvogel.de/2012/03/14/cron-jobs-fur-sonnenauf-untergang/
+ */
+/*
+ * This file is part of sun
+ *
+ * sun is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * any later version.
+ *
+ * sun is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with sun. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <string.h>
+#include <getopt.h>
+#include <float.h>
+#include <math.h>
+
+#include "sun.h"
+
+static struct option long_options[] = {
+	{"twilight",	required_argument, 0, 't'},
+	{"date",	required_argument, 0, 'd'},
+	{"format",	required_argument, 0, 'f'},
+	{"lat",		required_argument, 0, 'a'},
+	{"lon",		required_argument, 0, 'o'},
+#ifdef GEONAMES_SUPPORT
+	{"query",	required_argument, 0, 'q'},
+#endif
+	{"zone",	required_argument, 0, 'z'},
+	{"help",	no_argument,	   0, 'h'},
+	{0}
+};
+
+static char *long_options_descs[] = {
+	"use special twilight (nautic|civil|astro)",
+	"calculcate for specified date (eg. 2011-12-25)",
+	"output format (eg. %H:%M:%S)",
+	"geographical latitude (-90° to 90°)",
+	"geographical longitude (-180° to 180°)",
+#ifdef GEONAMES_SUPPORT
+	"query geonames.org for geographical position",
+#endif
+	"use timezone for output",
+	"show this help"
+};
+
+void usage() {
+	printf("usage: sun mode [options]\n\n");
+	printf("  mode is one of: rise, set, noon, daytime, nighttime\n\n");
+	printf("  following OPTIONS are available\n");
+
+	struct option *op = long_options;
+	char **desc = long_options_descs;
+	while (op->name && desc) {
+		printf("\t-%c, --%s\t%s\n", op->val, op->name, *desc);
+		op++;
+		desc++;
+	}
+
+	printf("\nA combination of --lat, --lon or --query is required!\n");
+	printf("For bugs or feature requests please contact Steffen Vogel <stv0g@0l.de>\n");
+}
+
+char * strreplace(char *subject, char *search, char *replace) {
+	int new_len = strlen(subject);
+	int search_len = strlen(search);
+	int replace_len = strlen(replace);
+	char *tmp;
+
+	for (tmp = strstr(subject, search); tmp != NULL; tmp = strstr(tmp + search_len, search)) {
+		new_len += replace_len - search_len;
+	}
+
+	char *old = subject;
+	char *new = malloc(new_len);
+
+	new[0] = '\0'; /* empty string */
+	for (tmp = strstr(subject, search); tmp != NULL; tmp = strstr(tmp + search_len, search)) {
+		new_len = strlen(new);
+
+		strncpy(new + new_len, old, tmp - old);
+		strcpy(new + new_len + (tmp - old), replace);
+		old = tmp + search_len;
+	}
+
+	strcpy(new + strlen(new), old);
+
+	return new;
+}
+
+int main(int argc, char *argv[]) {
+	/* default options */
+	double twilight = -50.0 / 60; /* 50 Bogenminuten; no twilight, normal sunset/rise */
+	int timezone = 0; /* UTC */
+	char *format = "%H:%M";
+	char *query = NULL;
+	bool error = false;
+
+	enum mode mode;
+	struct coords pos = { INFINITY, INFINITY };
+	struct tm date;
+
+	/* default date: now */
+	time_t t;
+	time(&t);
+	localtime_r(&t, &date);
+
+	/* parse command */
+	if (argc <= 1) {
+		fprintf(stderr, "mode required\n\n");
+		error = true;
+	}
+	else if (strcmp(argv[1], "rise") == 0) mode = RISE;
+	else if (strcmp(argv[1], "set") == 0) mode = SET;
+	else if (strcmp(argv[1], "noon") == 0) mode = NOON;
+	else if (strcmp(argv[1], "daytime") == 0) mode = DAYTIME;
+	else if (strcmp(argv[1], "nighttime") == 0) mode = NIGHTTIME;
+	else {
+		fprintf(stderr, "invalid mode: %s\n", argv[1]);
+		error = true;
+	}
+
+	/* parse command line arguments */
+	while (1) {
+		int optidx;
+		int c = getopt_long(argc-1, argv+1, "ht:d:f:a:o:q:z:", long_options, &optidx);
+
+		/* detect the end of the options. */
+		if (c == -1) break;
+
+		switch (c) {
+			case 't':
+				if (strcmp(optarg, "civil") == 0) {
+					twilight = -6.0;
+				}
+				else if (strcmp(optarg, "nautic") == 0) {
+					twilight = -12.0;
+				}
+				else if (strcmp(optarg, "astro") == 0) {
+					twilight = -18.0;
+				}
+				else {
+					fprintf(stderr, "invalid twilight: %s\n", optarg);
+					error = true;
+				}
+				break;
+
+			case 'd':
+				if (strptime(optarg, "%Y-%m-%d", &date) == 0) {
+					fprintf(stderr, "invalid date: %s\n", optarg);
+					error = true;
+				}
+				break;
+
+			case 'f':
+				format = strdup(optarg);
+				break;
+
+			case 'a':
+				pos.lat = strtod(optarg, NULL);
+				break;
+
+			case 'o':
+				pos.lon = strtod(optarg, NULL);
+				break;
+#ifdef GEONAMES_SUPPORT
+			case 'q':
+				query = strdup(optarg);
+				break;
+#endif
+
+			case 'z':
+				timezone = atoi(optarg);
+				break;
+
+			case 'h':
+				usage();
+				return EXIT_SUCCESS;
+
+			case '?':
+			default:
+				error = true;
+		}
+	}
+
+#ifdef GEONAMES_SUPPORT
+	if (query && geonames_lookup(query, &pos, NULL, 0) != 0) {
+		fprintf(stderr, "failed to lookup location: %s\n", query);
+		error = true;
+	}
+#endif
+
+	if (pos.lat == INFINITY) {
+		fprintf(stderr, "please provide a complete position: latitude is missing\n");
+		error = true;
+	}
+	else {
+		if (fabs(pos.lat) > 90) {
+			fprintf(stderr, "invalid latitude: %.4f\n", pos.lat);
+			error = true;
+		}
+		else if (fabs(pos.lat) > 65) {
+			fprintf(stderr, "attention: results may be inaccurate! (delta_T > 5min)\n");
+		}
+	}
+
+	if (pos.lon == INFINITY) {
+		fprintf(stderr, "please provide a complete position: longitude is missing\n");
+		error = true;
+	}
+	else if (fabs(pos.lon) > 180) {
+		fprintf(stderr, "invalid longitude: %.4f\n", pos.lon);
+		error = true;
+	}
+
+	if (error) {
+		printf("\n");
+		usage();
+		return EXIT_FAILURE;
+	}
+
+#ifdef DEBUG
+	char date_str[64];
+	strftime(date_str, 64, "%Y-%m-%d", &date);
+	printf("calculate for %s\n", date_str);
+	printf("for position: %f, %f\n", pos.lat, pos.lon);
+	printf("with twilight: %f\n", twilight);
+#endif
+
+	/* start the calculation */
+	struct tm result = sun(pos, date, mode, twilight, timezone);
+
+	char result_str[64];
+
+	/* workaround for unix timestamps and 'struct tm's limitation on years > 1990 */
+	if (mode == DAYTIME || mode == NIGHTTIME) {
+		if (strstr(format, "%s") != NULL) {
+			result.tm_year = 70;
+			result.tm_mon = 0;
+			result.tm_mday = 1;
+			result.tm_hour++;
+
+			char buffer[16];
+			sprintf(buffer, "%lu", mktime(&result));
+
+#ifdef DEBUG
+			printf("buffer: %s\n", buffer);
+#endif
+
+			format = strreplace(format, "%s", buffer);
+
+			result.tm_hour--;
+
+#ifdef DEBUG
+			printf("format: %s\n", format);
+#endif
+		}
+
+		result.tm_year = -1900;
+		result.tm_mon = -1;
+		result.tm_mday = 0;
+	}
+
+	strftime(result_str, 64, format, &result);
+	printf("%s\n", result_str);
+
+	return EXIT_SUCCESS;
+}