<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 centre 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
>Location</guimenu
> menu. </para>
</tip>
</sect1>