Astroid is a particular type of curve: a hypocycloid with four cusps.
A circle of radius 1/4 rolls around inside a circle of radius 1 and a point on its circumference traces an astroid. A line segment of length 1 slides with one end on the x-axis and the other on the y-axis, so that it is tangent to the astroid. The parametric equations are:
x = (cos(p))^3
y = (sin(p))^3
To plot function Astroid use the folowing script: