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abstraction > mathematical concept > geometrical object > conic section > ellipse > circle > great circle > meridian
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meridian comparison table
Subject is a kind of has definition
great circlecircleA circle on the surface sphere whose diameter equal to the diameter of the sphere.
meridiangreat circleA great circle passing through the celestial poles and through the zenith of any location on Earth. For planetary observations a meridian is half the great circle passing through the planet's poles and through any location on the planet.

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