Curves59 of 113
Astroid
Ole Rømer, 1674; named by Littrow, 1838
A hypocycloid with four cusps: a circle rolls inside another of four times its radius, and a point on its rim traces the curve. It is also the envelope of a ladder of fixed length sliding with one end on each of two perpendicular lines. Littrow named it in 1838, from the Greek for star.
x = a cos³t, y = a sin³t
On mathcurve.com as Astroïde