An introduction to the astrolabe, this site provides a clear, detailed account of the astronomical instrument's history and the principles behind its operation, with several large colour photographs. There is a small collection of annotated links to other sites in the same field, and a good brief critical bibliography. The site is maintained by Janus, a commercial company producing replicas of historical astronomical instruments: their "personal astrolabe" is advertised for sale here, but the commercial content is limited and does not prejudice the remainder of the site. Also available, downloadable at no charge, is a computer simulation known as the "electric astrolabe".

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