Topic summary
Keck Observatory

Extracted from the Wikipedia article W. M. Keck Observatory.
Overview
Each Keck telescope sits on an altazimuth mount. Most current 8–10 m class telescopes use altazimuth designs for their reduced structural requirements compared to older equatorial designs. Altazimuth mounting provides the greatest strength and stiffness with the least amount of steel, which, for Keck Observatory, totals about 270 tons per telescope, bringing each telescope's total weight to more than 300 tons. Two proposed designs for the next generation 30 and 40 m telescopes use the same basic technology pioneered at Keck Observatory: a hexagonal mirror array coupled with an altazimuth mounting.