equant

The Earth was still regarded as the central object in the Universe, but everything else revolved around the equant points, not around the Earth itself.

The big circle centred on the equant point is called a deferent.

Furthermore, the system was often criticized as being unduly complicated, while the need for equant points made many thinkers uneasy—it raised doubts about whether the Earth ought really to be regarded as the centre of the Universe.

The equant was a device for speeding up and slowing down the movement of a body in the heavens by measuring its movement not from the centre of a circle but from another point.

Still, they were fascinated by the simplicity of his techniques for calculation, and thrilled at the idea that it might be possible to junk the equant.