light, the usable optical aperture at any given time was 9.2 m. After a multi-year upgrade completed on July 29, 2015, the usable optical aperature was increased to 10m. The mirror itself is composed of 91 hexagonal segments, a segmented mirror design like the Keck telescopes. Updates to the telescope have increased its field of view from 4 arcminutes to 22 arcminutes (a full moon is 30 arcminutes for comparison). The telescope mirrors are aligned within a fraction of a wavelength of visible light by actuators under each segment. The tower next to the telescope, called the Center of Curvature Alignment Sensor Tower (CCAS), is used to calibrate the mirror segments. One of the advantages of this telescope design is that it was over 5 times more cost efficient for its aperture size than a more traditional design. As reported in Nature of 28 November 2012, astronomers have used the Hobby–Eberly Telescope to measure the mass of an extraordinarily large black hole (with mass approximates 17 billion Suns), possibly the largest black hole found so far. It has been found in the compact, lenticular galaxy NGC 1277, which lies 220 million light-years away in the constellation Perseus. The black hole has approximately 59 percent of the mass of the bulge of this spiral galaxy (14 percent of the total stellar mass of the galaxy). The Habitable Zone Planet Finder is a spectrograph for the Hobby–Eberly Telescope capable of detecting earth like planets. The design of the Hobby-Eberly was used as the basis for the Southern African Large Telescope. See also List of largest optical reflecting telescopes Southern African Large Telescope List of the largest optical telescopes in the contiguous United States List of largest optical telescopes in the 20th century References External links HET General Information Page Optical telescopes University of Texas at Austin