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+<sect1 id="ai-zenith">
+<sect1info>
+<author>
+<firstname>Jason</firstname>
+<surname>Harris</surname>
+</author>
+</sect1info>
+<title>The Zenith</title>
+<indexterm><primary>Zenith</primary>
+<seealso>Horizontal Coordinates</seealso>
+</indexterm>
+<para>
+The Zenith is the point in the sky where you are looking when you look
+<quote>straight up</quote> from the ground. More precisely, it is the point on
+the sky with an <firstterm>Altitude</firstterm> of +90 Degrees; it is the Pole
+of the <link linkend="horizontal">Horizontal Coordinate
+System</link>. Geometrically, it is the point on the <link
+linkend="ai-csphere">Celestial Sphere</link> intersected by a line drawn from
+the center of the Earth through your location on the Earth's surface.
+</para><para>
+The Zenith is, by definition, a point along the <link
+linkend="ai-meridian">Local Meridian</link>.
+</para>
+<tip>
+<para>Exercise:</para>
+<para>
+You can point to the Zenith by pressing <keycap>Z</keycap> or by selecting
+<guimenuitem>Zenith</guimenuitem> from the <guimenu>Pointing</guimenu> menu.
+</para>
+</tip>
+</sect1>