Final answer:
Large astronomical telescopes utilize multiple hexagonal mirrors arranged to function as a single large mirror, with active control for precision. The Keck telescopes and the in-construction European Extremely Large Telescope are examples of this technology in action.
Step-by-step explanation:
The construction of large astronomical telescopes involves the assembly of primary mirrors from numerous smaller hexagonal mirrors. These are precisely aligned and controlled to function as a single large mirror. The Keck telescopes were pioneers in this with their 10-meter mirrors made up of 36 hexagonal sections. Similarly, the European Extremely Large Telescope (E-ELT) is under construction and will feature a massive 39.3-meter mirror composed of 798 hexagonal mirrors. The design of these telescopes allows for active control of each mirror segment, enabling the correction of any distortions in real-time and ensuring the collection of high-resolution images and spectra. Such large telescopes, like the Thirty Meter Telescope, are essential for cutting-edge astronomical discoveries, including the search for extraterrestrial life through the study of planets around other stars.