A hypocycloid is a curve formed by the path of a point attached to a smaller circle as it rolls around inside a larger circle. Related curves are the hypotrochoid, epicycloid and epitrochoid. My other YouTube channels: The Science Fiction Rock Experience ( the music show I produce): null My science and music channel:: null Science World (with Emrah Polat): null My website: https://www.daviddarling.info/ My latest book is available here: https://oneworld-publications.com/work/the-biggest-number-in-the-world/