<sect1 id="ai-meridian">
<sect1info>
<author
><firstname
>Jason</firstname
> <surname
>Harris</surname
> </author>
</sect1info>
<title
>The Local Meridian</title>
<indexterm
><primary
>Local Meridian</primary>
<seealso
>Hour Angle</seealso
> <seealso
>Celestial Sphere</seealso
> </indexterm>
<para
>The Local Meridian is an imaginary <link linkend="ai-greatcircle"
>Great Circle</link
> on the <link linkend="ai-csphere"
>Celestial Sphere</link
> that is perpendicular to the local <link linkend="ai-horizon"
>Horizon</link
>. It passes through the North point on the Horizon, through the <link linkend="ai-cpoles"
>Celestial Pole</link
>, up to the <link linkend="ai-zenith"
>Zenith</link
>, and through the South point on the Horizon. </para
><para
>Because it is fixed to the local Horizon, stars will appear to drift past the Local Meridian as the Earth spins. You can use an object's <link linkend="equatorial"
>Right Ascension</link
> and the <link linkend="ai-sidereal"
>Local Sidereal Time</link
> to determine when it will cross your Local Meridian (see <link linkend="ai-hourangle"
>Hour Angle</link
>). </para>
</sect1>