Wolfram Research
Wolfram Mathworld: Astroid
Find out how an astroid is related to the ellipse at this math page. This page starts with describing how an astroid may be created easily with two concentric circles with a given ratio, the site then goes into details regarding the...
Other
Personal: Astroid
Excellent personal site! Gives the complete history of the astroid and has lots of pictures, graphs, and even videos!
University of St. Andrews (UK)
University of St. Andrews: Asteroid
This site, which is provided for by the University of St. Andrews, shows the graph of an asteroid and gives the parametric and cartesian equations.
Other
College of the Redwoods: Special Plane Curves
This resource gives a report on asteroids including brief history and pictures.
University of St. Andrews (UK)
University of St. Andrews: Astroid
This site from the University of St. Andrews allows you to zoom in/out and add evolutes, involutes, etc.