On July 24, 2014, Dr. Richard Green gave a lecture at NAOC introducing the facilities at Steward Observatory and the newly-completed Large Binocular Telescope (LBT). Dr. Green is the assistant director at Steward Observatory, which is administered by the University of Arizona. Dr. Green described the wide variety of telescopes and instruments managed by Steward Observatory, including an impressive selections of radio, infrared and optical telescopes and their associated spectrometers. He mentioned that, in addition to the more recent telescopes with large diameters, a number of legacy telescopes with smaller apertures are still being operated for use in surveys and education. In addition to showcasing the facilities, Dr. Green discussed the astronomy department at the University of Arizona. In particular, the Center for Astronomy Education there is a leader in developing instructional materials and outreach activities. Dr. Green went on to say that the University of Arizona's astronomy department welcomes collaborative research activities with NAOC.
For the remainder of his presentation, Dr. Green showcased the design, construction and abilities of the LBT. The LBT has two 8-meter mirrors, which can work in combination to give the same performance as a single 12-meter mirror. He explained and showed photos of the advanced method used for making the mirror, which involved pouring high-quality molten glass into a rotating mold containing a honeycomb cast. Later, when the glass cooled and the honeycomb cast was removed, the mirrors composing the LBT could be large but also relatively flexible and light. He also showed the system of 130 pneumatic actuators attached to the backs of the mirrors which control flexure and maintain a nearly-ideal shape. In addition, he exhibited photos of one of the large mirrors being transported to the remote site where the LBT is located, a process that required a custom-made truck that drove only 2 km per hour over three days.
The pair of mirrors mounted in the LBT can operate independently to acquire data from two different instruments on the same target, or together as an interferometer for high-resolution measurements. The facility also incorporates an advanced active optics system that can achieve a Strehl ratio of 85%. He showed images of exoplanetary systems and close multiple star systems taken with the LBT, demonstrating its excellent resolving ability, which can even exceed that of the Hubble Space Telescope. These capabilities will allow the LBT to contribute to advances in many fields of astronomy.
After the presentation, during the question and answer session, one attendee asked Dr. Green about how light pollution could affect the performance of the LBT. Dr. Green gave a frank explanation about the detrimental effects of light pollution on the LBT, especially from the nearby cities of Tucson and Phoenix. He mentioned that, generally speaking, towns and other organizations in the vicinity of LBT are supportive of efforts to control light pollution and maintain dark skies, but that this effort requires ongoing discussions with all parties involved, especially considering economic drivers in the area. Dr. Green is optimistic that, with a concerted effort and support from nearby communities, a dark sky could be maintained around the LBT.
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