The Hobby–Eberly Telescope at McDonald Observatory in West Texas is one of the world’s largest optical telescopes and is notable for a cost-saving design that fixes its main mirror at a 55-degree angle while tracking objects with rotating structure and moving instruments. Its primary mirror is made of 91 precisely aligned hexagonal segments, and upgrades completed in 2015 expanded its effective aperture to 10 meters and greatly widened its field of view. Built for spectroscopy, it has supported research from the Solar System to distant galaxies, including planet detection, supernova studies, galaxy rotation measurements, black hole mass estimates, and dark energy investigations through HETDEX.