A sphere is a solid globelike figure. Its <I>surface</I> consists of all points a certain distance from a fixed point called the <I>center.</I> The <I>radius</I> is the distance from the center to the surface. The <I>diameter</I> equals twice this distance. If a <I>plane</I> (flat surface) passes through the center, it produces a <I>great circle.</I>
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World Book diagram by Laura Lee Lizak</P>
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