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+/**
+ * Copyright © 2016  Mattias Andrée <maandree@member.fsf.org>
+ * 
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ * 
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ * 
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+
+
+/**
+ * The times of the day, by degree of darkness.
+ */
+enum darkness {
+	/**
+	 * Not calculated yet.
+	 */
+ 	UNKNOWN = -1,
+
+	/**
+	 * Hopefully, it is bright outside.
+	 */
+	DAYTIME = 0,
+
+	/**
+	 * The sky is golden. The golden "hour".
+	 * Also known as BMCT (dawn) or EECT (dusk).
+	 */
+	CIVIL_TWILIGHT = 1,
+
+	/**
+	 * The sky is pink and blue.
+	 */
+	NAUTICAL_TWILIGHT = 2,
+
+	/**
+	 * The sky is medium dark blue.
+	 */
+	ASTRONOMICAL_TWILIGHT = 3,
+
+	/**
+	 * The sky is reallu dark blue.
+	 */
+	NIGHT = 4
+};
+
+
+
+/**
+ * Is it daytime, night, perhaps some kind of twilight?
+ * 
+ * @param    elevation  The Sun's apparent elevation.
+ * @return              The time of the day.
+ */
+enum darkness get_darkness(double elevation);
+