PROGRESS IN GROUND-BASED OPTICAL TELESCOPES

For several decades, the 5 metre Palomar telescope has set a practical limit to the size of ground-based optical telescopes only exceeded by the Russian 6 metre telescope. Using new technologies to produce eith er large monolithic mirrors or large mosaic of smaller elements, astro nomers in Europe, the United States and Japan are developing a new gen eration of telescopes. Not only are these new telescopes much bigger i n size, offering considerably more collecting power, but they also pro vide a much better angular resolution. To achieve this they rely heavi ly on computer control techniques and advanced modelling. Even more pr ogress in angular resolution is expected when modern techniques such a s adaptive optics and interferometry, which are being implemented on m ost of the new telescopes, are fully operational. This article evaluat es the impact of new technologies on the development of large optical telescopes, in particular on the realization of their optics. The key mirror technologies are reviewed and a particular project, the ESO VLT is reviewed in some more detail as an illustration.