<sect1 id="ai-cequator">
<sect1info>
<author>
<firstname>Jason</firstname>
<surname>Harris</surname>
</author>
</sect1info>
<title>The Celestial Equator</title>
<indexterm><primary>Celestial Equator</primary>
<seealso>Equatorial Coordinates</seealso>
</indexterm>
<para>
The <firstterm>Celestial Equator</firstterm> is an imaginary <link 
linkend="ai-greatcircle">great circle</link> on the <link 
linkend="ai-csphere">celestial sphere</link>.  The celestial equator
is the fundamental plane of the <link linkend="equatorial">Equatorial
Coordinate System</link>, so it is defined as the locus of points 
with Declination of zero degrees.  It is also the projection of the 
Earth's equator onto the sky.
</para>
<para>
The Celestial Equator and the <link linkend="ai-ecliptic">Ecliptic</link> 
are set at an angle of 23.5 degrees in the sky.  The points where they 
intersect are the Vernal and Autumnal <link 
linkend="ai-equinox">Equinoxes</link>.
</para>
</sect1>