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)
Hobby–Eberly Telescope achieving first light in 1996, the telescope has been used for a wide variety of studies ranging from the Solar System to stars in our galaxy and studies of other galaxies. The telescope has been used successfully to find planets orbiting around other stars by measuring radial velocities as precisely as 1 m/s. Using the low-resolution spectrograph, the telescope has been used to identify Type Ia supernovae to measure the acceleration of the universe. The telescope has also been used to measure the rotation of individual galaxies. The telescope was upgraded for use in the Hobby–Eberly Telescope Dark Energy Experiment