Definition:Sphere/Geometry/Axis
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Definition
By definition, a sphere is made by turning a semicircle around a straight line.
That straight line is called the axis of the sphere.
In the words of Euclid:
- The axis of the sphere is the straight line which remains fixed about which the semicircle is turned.
(The Elements: Book $\text{XI}$: Definition $15$)
Linguistic Note
The plural of axis is axes, which is pronounced ax-eez not ax-iz.
Compare basis.