University of St. Andrews (UK)
University of St. Andrews: Non Euclidean Geometry
The University of St. Andrews in Scotland provides an excellent site explaining Non-Euclidean geometry.
Wolfram Research
Wolfram Math World: Geometry
This MathWorld tutorial provides detailed overviews of the concepts and theorems associated with geometry. Most of the Math World sites are extensive and some require higher math knowledge to understand, links to terms and topics are...
Oswego City School District
Regents Exam Prep Center: Lines and Planes
Use these resources in preparing instruction on undefined terms (points, lines, and planes), theorems relating lines and planes, and Euclidean and non-Euclidean geometry. You'll find three lessons on the aforementioned subject areas, an...
Wikimedia
Wikipedia: Hyperbolic Geometry
This encyclopedia entry from Wikipedia offers a discussion on hyperbolic geometry. The site explains how the hyperbolic geometry plane is represented in two dimensions and how lines in the plane must be drawn. Other types of models for...
National Council of Teachers of Mathematics
The Math Forum: Ask Dr. Math: Hyperbolic Geometry
Dr. Math, responds to a question fro a nineth grade stduent who wants to understand hyperbolic geometry. The Dr. uses descriptive analogies in attempts to unravel why triangles in hyperbolic geometry have less than 180 degrees in them.
Wolfram Research
Wolfram Mathworld: Elliptic Geometry
MathWorld offers a brief definition of elliptic geometry and including a brief discussion of its relationship to Euclidean geometry, with links to other related definitions.
Wikimedia
Wikipedia: Spherical Geometry
Wikipedia, a publicly-maintained encyclopedia, provides an explanation of spherical geometry along with a listing of its most important uses.
Wolfram Research
Wolfram Math World: Spherical Geometry
Site provides a brief explanation of the discipline of Spherical Geometry along with many links to spherical geometry topics.
Shodor Education Foundation
Shodor Interactivate: Lesson: The Mandelbrot Set
In this instructional activity students will explore Julia sets and the Mandelbrot set. In the process they will learn about fractals and explore complex numbers and function iteration.
Math Words
Math words.com: Elliptic Geometry
The basic definition for what elliptic geometry is is found here.
Wikimedia
Wikipedia: Elliptic Geometry
This encyclopedia article contains a basic description of what elliptic geometry is.
Boston University
Bu: Fractal Geometry of the Mandelbrot Set
This site progresses in iterations through Mandelbrot and Julia sets to explain fractals and the mathematics behind them.
Dartmouth College
Dartmouth College: The Different Styles of Euclid and Copernicus
A history of the differences between Euclid's and Copernicus's methods of proving geometric ideas.
Boston University
Boston University: Chaos, Fractals and Arcadia
This is an interesting site for information on chaos and fractals. Includes links to interactive activities to learn more.
Shodor Education Foundation
Shodor Interactivate: Lesson: Fractals
This site provides some links to activities and lesson plans dealing with fractals and chaos.
Other
Eal: Fract Ed
A great resource for beginners. The site begins with a definition of iteration of functions, and proceeds from there to discuss fractal dimension.