solutions 1/2006 – additional informations

100 Years of Astronomical Mirrors from SCHOTT

In 1906, the Heidelberg Observatory in Germany made use of the world’s very first large-scale mirror telescope. It was equipped with a mirror made of optical glass from SCHOTT that was 720 millimeters in size. During the decades that followed, the company continued to cast larger and larger mirror substrates for telescopes that were becoming more and more sensitive to light intensities. These substrates were initially made of crown glass and later from glasses with a lower degree of thermal expansion that were able to deliver more consistent imaging characteristics.

In the early 1970’s, SCHOTT set a milestone by developing its glass ceramic product, ZERODUR®. Between 1993 and 1996, SCHOTT poured the largest monolithic mirror substrates made of this material, with a width of 8.20 meters, for use in the four eso telescopes for the VLT (Very Large Telescope) on top of the Cerro Paranal in Chile. Even larger telescopes were produced by assembling hexagonal segments. For example, the 10.4-meter telescope grantecan that is currently being built on La Palma consists of 36 mirror substrate segments. In the future, mirror telescopes with diameters of 30 or even 100 meters will be possible. Here, too, ZERODUR® is certain to remain the material of choice.