University of St. Andrews (UK)
University of St. Andrews: Mariner's Astrolabe (1616)
A page on the Mariner's Astrolabe describes its origins and how it is used. A photo also accompanies the article.
Other
Astrolabe.org: The Astrolabe
A description of the ancient astrolabes and how they worked. Provides information about definitions, collections, and also includes photos.
Other
The Astrolabe: Home Page
This site provides a very general overview of astrolabe principles with links to other pages for more detailed information.