A circle of a sphere is a circle defined as the intersection of a sphere and a plane. If the plane contains the center of the sphere then the circle is called a great circle, otherwise it is a small circle. Circles of a sphere have radius less than or equal to the radius sphere, with equality when the circle is a great circle.
In the geographic coordinate system on a globe, the parallels of latitude are such circles, with the Equator the only great circle. By contrast, all meridians of longitude, paired with their opposite meridian in the other hemisphere, form great circles.
The diameter of the sphere which passes though the center of the circle is called its axis and the endpoints of this diameter are called its poles. A circle of a sphere can also be defined as the set of points at a given angular distance from a given pole.
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Famous quotes containing the words circle of, circle and/or sphere:
“And year by year our memory fades
From all the circle of the hills.”
—Alfred Tennyson (1809–1892)
“... [a] girl one day flared out and told the principal “the only mission opening before a girl in his school was to marry one of those candidates [for the ministry].” He said he didn’t know but it was. And when at last that same girl announced her desire and intention to go to college it was received with about the same incredulity and dismay as if a brass button on one of those candidate’s coats had propounded a new method for squaring the circle or trisecting the arc.”
—Anna Julia Cooper (1859–1964)
“A knowledge of the Globe and its various inhabitants, however slight ... has a kindred effect with that of seeing them as travellers, which never fails, in uncorrupted minds, to weaken local prejudices, and enlarge the sphere of benevolent feelings.”
—James Madison (1751–1836)