1 <sect1 id="ai-greatcircle">
4 <firstname>Jason</firstname>
5 <surname>Harris</surname>
8 <title>Great Circles</title>
9 <indexterm><primary>Great Circles</primary>
10 <seealso>Celestial Sphere</seealso>
13 Consider a sphere, such as the Earth, or the
14 <link linkend="ai-csphere">Celestial Sphere</link>. The intersection
15 of any plane with the sphere will result in a circle on the surface of
16 the sphere. If the plane happens to contain the center of the sphere,
17 the intersection circle is a <firstterm>Great Circle</firstterm>.
18 Great circles are the largest circles that can be drawn on a sphere.
19 Also, the shortest path between any two points on a sphere is always
22 Some examples of great circles on the celestial sphere include: the
23 <link linkend="ai-horizon">Horizon</link>, the
24 <link linkend="ai-cequator">Celestial Equator</link>, and the
25 <link linkend="ai-ecliptic">Ecliptic</link>.