Galileo demonstrates one of his telescopes to the ruler of Venice in August 1609 (Galileo is standing to the right of the telescope)
(Image: Science Photo Library: from <a href="http://eu.wiley.com/WileyCDA/WileyTitle/productCd-3527408657.html"><i>Eyes on the Skies: 400 Years of Telescopic Discovery</i></a> by Govert Schilling and Lars Lindberg Christensen)
In celebration of the International Year of Astronomy in 2009, 91av takes you on an armchair tour of some of the most important telescopes ever built.
