A light source at the radiant point S produces some radial light rays (in yellow). The rays are reflected by the hyperbola. If the rays have more than one intersection point with the hyperbola, they are reflected at both points. The reflected rays and their continuations are shown in light blue.[br][br]Definition: The envelope of the reflected rays by the hyperbola is called the [i]catacaustic[/i] of the hyperbola (also called [i]caustic[/i]).[br][list][br][*]Drag the slider - "numberRays" to change the number of light rays.[br][*]Drag the slider - "d" to change the distance from the center of the hyperbola to the radiant point.[br][*]Drag the slider -"[math]\alpha[/math]" to rotate the radiant point around the center of the hyperbola.[br][*]To experiment with the catacaustic, select different values for the distance ([math]c[/math]) from the center of the hyperbola to its foci, and for the distance ([math]a[/math]) from the center of the hyperbola to the vertices of the hyperbola .[br][/list]