However, a sphere like the Earth is spinning. A spinning sphere has an axis of rotation, two poles and a circle between the poles dividing the sphere into two hemispheres. Latitude These points and circle allow us to define one of our terrestrial coordinates. The circle between the two poles is called the Equator . It is a Great Circle .
Great circles are circles drawn on a sphere with the same radius as the sphere.
The Equator is the zero for Latitude . Lines of Latitude can be run north and south of the Equator. These are a series of Small Circles and are shown on the left sphere below. Small circles are circles drawn on a sphere that are smaller than the sphere. Zero Latitude is the Equator.