Definition:Pole of Circle

Definition

Let $S$ be a sphere whose center is $O$.

Let $AB$ be a diameter of $S$, such that $A$ and $B$ are the points of intersection of $AB$ with $S$.

Let $C$ be a (small) circle of $S$ embedded in a plane perpendicular to $AB$.

The points $A$ and $B$ are the poles of the circle $C$.

Special Case: Pole of Great Circle

Let $C$ be a great circle of $S$.

Let $AB$ be the diameter of $S$ situated perpendicular to the plane of $C$.

The points $A$ and $B$, where the diameter intersects $S$, are the poles of the great circle $C$.

Also see

• Results about poles of circles can be found here.

Sources

• 1976: W.M. Smart: Textbook on Spherical Astronomy (6th ed.) ... (previous) ... (next): Chapter $\text I$. Spherical Trigonometry: $2$. The spherical triangle.
• 1998: David Nelson: The Penguin Dictionary of Mathematics (2nd ed.) ... (previous) ... (next): pole: 2. (of a circle on a sphere)
• 2008: David Nelson: The Penguin Dictionary of Mathematics (4th ed.) ... (previous) ... (next): pole: 2. (of a circle on a sphere)