larger than the 5-meter Hale or 6-meter BTA-6 is prohibitively expensive due to the cost of both the mirror, and the massive structure needed to support it. A mirror beyond that size would also sag slightly under its own weight as the telescope is rotated to different positions, changing the precision shape of the surface, which must be accurate to within 2 millionths of an inch (50 nm). Modern telescopes over 9 meters use a different mirror design to solve this problem, with either a single thin flexible mirror or a cluster of smaller segmented mirrors, whose shape is continuously adjusted by a computer-controlled active optics system using actuators built into the mirror support cell. Dome The moving weight of the upper dome is about 1000 US tons, and can rotate on wheels. The dome doors weigh 125 tons each. The dome is made of welded steel plates about 10 mm thick. Observations and research The first observation of the Hale telescope was of NGC 2261 on January 26, 1949. During its first 50 years, the Hale telescope made many significant contributions to stellar evolution, cosmology, and high-energy astrophysics. Similarly, the telescope, and the technology developed for it, advanced the study of the spectra of stars, interstellar matter, AGNs, and quasars. Quasars were first identified as high redshift sources by spectra taken with the Hale telescope. Halley's Comet (1P) upcoming 1986 approach to the Sun was first detected by astronomers David C. Jewitt and G. Edward Danielson on 16 October 1982 using the 200-inch Hale telescope equipped with a CCD camera. Two moons of the planet Uranus were discovered in September 1997, bringing the planet's total known moons to 17 at that time. One was Caliban (S/1997 U 1), which was discovered on 6 September 1997 by Brett J. Gladman, Philip D. Nicholson, Joseph A. Burns, and John J. Kavelaars using the 200-inch Hale telescope. The other Uranian moon discovered then is Sycorax (initial designation S/1997 U 2) and was also discovered using the 200 inch Hale telescope. The Cornell Mid-Infrared Asteroid Spectroscopy (MIDAS) survey used the Hale Telescope with a spectrograph to study spectra from 29 asteroids. An example of a result from that study, is that the asteroid 3 Juno was determined to have average radius of 135.7±11 km using the infrared data. In 2009, using a coronograph, the Hale telescope was used to discover the star Alcor