Almost 20 years — from 1975 until 1993, when earned first telescope Keck Observatory — Russia (or, to speak officially, the Soviet Union) has the world’s largest optical telescope. The diameter of the primary mirror Large Telescope Alt-azimuth, which is located on the mountain Pastukhova, located in the Caucasus, between the Black and Caspian Seas, is 238 inches (6.05 meters). The decision to create BTA was made in 1960. He surpassed in size mounted on Mount Palomar 200-inch Hale Telescope and gave Russian astronomers serious cause for boasting.
However, in spite of the world’s largest mirror, the telescope best ever been before. First, the mountain is notorious for bad Pastukhova atmospheric visibility, strong winds and changeable weather. Besides the huge dome of the laboratory, a height of 58 meters, is excessive. Its concrete steel and make it practically impossible to maintain within the same temperature as the outside, and this further deteriorates optical characteristics. Although other observatories observations with a resolution of less than a second of arc are quite common, astronomer, using the BTA, at best, will be allowed in the two seconds of arc. This makes a great telescope is quite useless for imaging applications, although its huge light-collecting ability proved very useful for the spectroscopy of weak cosmic objects.
All of these problems would be tolerable if it were not for the quality of the telescope optics, which from the beginning was low. The first mirror blank for its failed. Opticians near Moscow Lytkarino Optical Glass had no serious experience working with such large mirrors and it was cooled too quickly. As a result, there have cracks and bubbles that made it useless.
Since the second workpiece fared better, but also not perfect. When it was installed, it was discovered that she had a number of serious shortcomings. Observatory staff even had to block part of the optical path of a black cloth. Finally, in 1978, established the third mirror telescope — no cracks and better surface quality.
However, this problem with the optics for BTA is not over. According to Alexei Moiseyev, an astronomer of the Special Astrophysical Observatory (SAO) of the Russian Academy of Sciences, which manages the telescope primary mirror surface gradually damages the repeated washing of alkaline solutions before recoating aluminum. "Apply the new reflective layer, not polishing the mirror again, it will be impossible," — explains Moses. However, the new polish would be easy to work with a six-meter telescope, the schedule of observations which already overloaded.
Initially, engineers wanted to replace the Observatory Mirror pyroceramics having a low thermal coefficient of expansion, partly to solve the temperature problem. However, it does not have enough money, so they decided to remake an old mirror, lying without the use of nearly 30 years.
In mid-2007, 42-ton block of glass gently moved from the Caucasus to Litkarino. It took three and a half weeks. The plant Optics decided to deal with the flaws surface only possible way — Grind them!
Catherine Kuchaeva, one of the vice-director of the observatory, recently told me the latest details on the progress of a cost of EUR 5 million renovation process mirrors. Milling machine removed from the surface of the glass 8 millimeters (more than half a ton!), Removing all the flaws. Now it’s up additional grinding and polishing. "The new optical technologies make it possible to reconstruct the surface of the 6-meter mirror — she explains — remove existing flaws and create an almost perfect parabolic surface, which significantly increase the angular resolution of the telescope."
Cosmologist at the University of Alabama William Keel (William Keel), which used BTA in 1990, following closely behind the project. "Delete 8 mm surface 6-meter mirror is not easy, but it makes it possible to keep the existing mirror and do not interrupt the performance of the telescope for this — he said. — They can also take advantage of the new technologies of control and grinding, which was not in 1975. "
According Kuchaeva CAO expects that the updated mirror will return to the observatory in the middle of 2013. It will then be covered with aluminum and installed in place of the current mirror. This is, of course, will be an important event for the Russian astronomers, after the collapse of the Soviet Union suffered from a lack of stable funding and modern equipment. Perhaps the "Caucasian Cyclops" in the end take a well-deserved place among the best telescopes in the world.
Kelly Beatty (Kelly Beatty)