History of the telescope a wider field of view than a classic Cassegrain. During the period 1850–1900, reflectors suffered from problems with speculum metal mirrors, and a considerable number of "Great Refractors" were built from 60 cm to 1 metre aperture, culminating in the Yerkes Observatory refractor in 1897; however, starting from the early 1900s a series of ever-larger reflectors with glass mirrors were built, including the Mount Wilson 60-inch (1.5 metre), the 100-inch (2.5 metre) Hooker Telescope (1917) and the 200-inch (5 metre) Hale telescope (1948); essentially all major research telescopes since 1900 have been reflectors. A number of 4-metre class (160 inch)
Discovery Channel Telescope Channel Telescope. When the comet approached Earth within 2.2 million miles (about 9 lunar distances), the size of the nucleus to be calculated to be 250 meters (820 feet) in diameter. The object was discovered by a PanSTARRS telescope, but not identified as a comet at that time. In 2017, DCT achieved 282 nights out of the year (365 days) of scheduled observations for science. At , the DCT is the fifth largest optical telescope in the continental United States, following the Hobby-Eberly Telescope segmented telescope, the Large Binocular Telescope twin telescopes, the MMT telescope, and the Hale telescope. Discovery