A curve traced by a point on the circumference of a circle rolling on the exterior of another circle.
- ‘He also investigated caustic curves and in particular he studied these associated curves of the parabola, the logarithmic spiral and epicycloids around 1692.’
- ‘Galileo defended the ‘epicycloids’ of Copernicus, even though Kepler already had presented a much better theory.’
- ‘The nephroid is the epicycloid formed by a circle of radius a rolling externally on a fixed circle of radius 2a.’
- ‘These are the epicycloid, the epitrochoid, the hypocycloid and the hypotrochoid and they are traced by a point P on a circle of radius b which rolls round a fixed circle of radius a.’