Wolfram Research
Wolfram Math World: Sphere
This webpage thoroughly discusses the math of spheres. Includes the equation for a sphere in Cartesian and spherical coordinates as well as parametrically. Surface Area, volume, and curvature are addressed at this extensive site.
National Council of Teachers of Mathematics
The Math Forum: Ask Dr. Math: Equation of a Sphere
Learn about how many points determine a unique sphere and how many points are needed to create a family of spheres. Dr. Rob works out the equation of a family of spheres given three points and then the equation of a unique sphere can be...