Large telescope size comparison. Artwork of the Keck telescope compared to four proposed new optical telescopes. From left to right: Keck Telescope (10 metre diameter mirror, 31 metre tall enclosure), Giant Magellan Telescope (GMT, 24.5 metre wide primary mirror, 50 metre tall enclosure), Large Synoptic Survey Telescope (LSST, 8 metre primary mirror, 43 metre tall enclosure), Thirty Meter Telescope (TMT, 30 metre diameter primary mirror, 66 metre diameter dome enclosure) and in the background, the European Extremely Large Telescope (E-ELT, 42 metre diameter primary mirror, 80 metre tall enclosure). At far right are silhouettes of two humans and a car.