Thanks to telescopes, scientists have made amazing discoveries: they discovered a huge number of planets beyond solar system learned about the existence of black holes at the centers of galaxies. But the Universe is so huge that this is only a grain of knowledge. Here are ten current and future giants of ground-based telescopes that give scientists the opportunity to study the past of the universe and learn new facts. Perhaps with the help of one of them it will even be possible to detect the Ninth planet.
BigSouth Africantelescope (SALT)
This 9.2-meter telescope is the largest ground-based optical instrument in the southern hemisphere. It has been operating since 2005 and focuses on spectroscopic surveys (registers spectra various kinds radiation). The instrument can view about 70% of the sky observed in Sutherland, South Africa.
Keck I and II telescopes
The twin 10-meter telescopes at the Keck Observatory are the second largest optical instruments on Earth. They are located near the top of Mauna Kea in Hawaii. Keck I started operating in 1993. A few years later, in 1996, the Keck II. In 2004, the first adaptive optics system with a laser guide star was deployed at the combined telescopes. It creates an artificial star spot as a guide to correct atmospheric distortion when viewing the sky.
Photo: ctrl.info Great Telescope of the Canaries (GTC)
The 10.4-meter telescope is located on the peak of the extinct volcano Muchachos on the Canary island of Palma. It is known as an optical instrument with the largest mirror in the world. It consists of 36 hexagonal segments. GTC has several support tools. For example, the CanariCam camera, which is capable of examining the mid-range infrared light emitted by stars and planets. CanariCam also has unique ability block bright starlight and make faint planets more visible in photographs.
Photo: astro.ufl Arecibo Observatory Radio Telescope
It is one of the world's most recognizable ground-based telescopes. It has been operating since 1963 and is a huge 30-meter radio reflecting dish near the city of Arecibo in Puerto Rico. The huge reflector makes the telescope particularly sensitive. It is able to detect a weak radio source (distant quasars and galaxies that emit radio waves) in just a few minutes of observation.
Photo: physicsworld ALMA Radio Telescope Complex
One of the largest ground-based astronomical instruments is presented in the form of 66 12-meter radio antennas. The complex is located at an altitude of 5000 meters in the Atacama Desert in Chile. First Scientific research were held in 2011. ALMA radio telescopes have one important purpose. With their help, astronomers want to study the processes that took place over the first hundreds of millions of years after big bang.
Photo: Wikipedia Up to this point, we have been talking about already existing telescopes. But now many new ones are being built. Very soon they will begin to function and significantly expand the possibilities of science.
LSST
This is a wide-angle reflecting telescope that will take pictures of a certain area of the sky every few nights. It will be located in Chile, on top of Mount Sero Pachon. While the project is only in development. The full operation of the telescope is planned for 2022. Nevertheless, high hopes are already pinned on him. Astronomers expect LSST to give them the best view of those far away from the Sun celestial bodies Oh. Scientists also suggest that this telescope will be able to notice space rocks that could theoretically collide with the Earth in the future.
Photo: LSST Giant Magellan Telescope
The telescope, which is expected to be completed by 2022, will be located at the Las Campanas Observatory in Chile. Scientists believe that the telescope will have four times the ability to collect light compared to existing on this moment optical devices. With it, astronomers will be able to discover exoplanets (planets outside the solar system) and study the properties of dark matter.
Photo: Wikipedia Thirty meter telescope
The 30-meter telescope will be located in Hawaii, next to the Keck Observatory. It is planned that it will begin to operate in 2025-2030. The aperture of the device is capable of providing a resolution 12 times higher than that of the Hubble Space Telescope.
Photo: Wikipedia SKA radio telescope
SKA antennas will be deployed in South Africa and Australia. Now the project is still under construction. But the first observations are planned for 2020. The sensitivity of the SKA will be 50 times that of any radio telescope ever built. With its help, astronomers will be able to study signals from a younger universe - the time when the formation of the first stars and galaxies took place.
Photo: Wikipedia Extremely Large Telescope (ELT)
The telescope will be located on the Cerro Amazone mountain in Chile. It is planned that it will start working only in 2025. However, he has already become famous for the huge mirror, which will consist of 798 hexagonal segments with a diameter of 1.4 meters each. The technical characteristics of the ELT will allow it to study the composition of the atmospheres of extrasolar planets.
Photo: Wikipedia The first telescopes with a diameter of just over 20 mm and a modest magnification of less than 10x, which appeared at the beginning of the 17th century, made a real revolution in the knowledge of the cosmos around us. Today, astronomers are preparing to commission gigantic optical instruments thousands of times larger in diameter.
May 26, 2015 was a real holiday for astronomers around the world. On this day, Hawaii Governor David Egay authorized the start of the zero cycle of construction near the summit of the extinct Mauna Kea volcano of a giant instrument complex, which in a few years will become one of the largest optical telescopes in the world.
The three largest telescopes of the first half of the 21st century will use different optical schemes. The TMT is built according to the Ritchey-Chrétien scheme with a concave primary mirror and a convex secondary one (both hyperbolic). The E-ELT has a concave primary mirror (elliptical) and a convex secondary mirror (hyperbolic). GMT uses Gregory's optical design with concave mirrors: primary (parabolic) and secondary (elliptical).
Giants in the arena
The new telescope is called the Thirty Meter Telescope (TMT) because its aperture (diameter) will be 30 m. If all goes according to plan, TMT will see the first light in 2022, and regular observations will begin another year later. The structure will be truly gigantic - 56 m high and 66 m wide. The main mirror will be composed of 492 hexagonal segments with a total area of 664 m². According to this indicator, TMT will surpass by 80% the Giant Magellan Telescope (GMT) with an aperture of 24.5 m, which in 2021 will come into operation at the Chilean Las Campanas Observatory, owned by the Carnegie Institution.
The 30-meter TMT telescope is built according to the Ritchey-Chrétien scheme, which is used in many currently operating large telescopes, including the largest on currently Gran Telescopio Canarias with a primary mirror 10.4 m in diameter. In the first phase, TMT will be equipped with three IR and optical spectrometers, with more scientific instruments planned to be added to them in the future.
However, the world champion TMT will not stay long. The opening of the European Extremely Large Telescope (E-ELT) with a record diameter of 39.3 m is scheduled for 2024, which will become the flagship instrument of the European Southern Observatory (ESO). Its construction has already begun at a three-kilometer altitude on Mount Cerro Armazones in Chile's Atacama Desert. The main mirror of this giant, composed of 798 segments, will collect light from an area of 978 m².
This magnificent triad will make up a group of next-generation optical supertelescopes that will have no competitors for a long time.
Anatomy of supertelescopes
The optical design of TMT goes back to a system that was independently proposed a hundred years ago by the American astronomer George Willis Ritchie and the Frenchman Henri Chrétien. It is based on a combination of a main concave mirror and a coaxial convex mirror of smaller diameter, both of which have the shape of a hyperboloid of revolution. Rays reflected from the secondary mirror are directed to the hole in the center of the main reflector and focused behind it. Using a second mirror in this position makes the telescope more compact and increases its focal length. This design has been implemented in many operating telescopes, in particular in the currently largest Gran Telescopio Canarias with a main mirror 10.4 m in diameter, in the 10-meter twin telescopes of the Hawaiian Keck Observatory and in the four 8.2-meter telescopes of the Cerro Paranal Observatory, owned by ESO.
The optical system of E-ELT also contains a concave primary mirror and a convex secondary, but it has a number of unique features. It consists of five mirrors, and the main one is not a hyperboloid, as in TMT, but an ellipsoid.
GMT is designed completely differently. Its main mirror consists of seven identical monolithic mirrors with a diameter of 8.4 m (six make up a ring, the seventh is in the center). The secondary mirror is not a convex hyperboloid, as in the Ritchey-Chrétien scheme, but a concave ellipsoid located in front of the focus of the primary mirror. In the middle of the 17th century, such a configuration was proposed by the Scottish mathematician James Gregory, and was first implemented in practice by Robert Hooke in 1673. According to the Gregorian scheme, the Large Binocular Telescope (Large Binocular Telescope, LBT) was built at the International Observatory on Mount Graham in Arizona (both of its "eyes" are equipped with the same primary mirrors as the GMT mirrors) and two identical Magellanic telescopes with an aperture of 6.5 m, which have been working at the Las Campanas Observatory since the early 2000s.
Strength is in the tools
Any telescope in itself is just a very large spotting scope. To turn it into an astronomical observatory, it must be equipped with highly sensitive spectrographs and video cameras.
TMT, which is designed for a service life of more than 50 years, will first of all be equipped with three measuring instruments mounted on a common platform - IRIS, IRMS and WFOS. IRIS (InfraRed Imaging Spectrometer) is a complex of video cameras very high resolution, providing a view in the field of 34 x 34 arc seconds, and an infrared spectrometer. IRMS is a multi-slit infrared spectrometer, while WFOS is a wide-angle spectrometer that can simultaneously track up to 200 objects in an area of at least 25 square arc minutes. The design of the telescope includes a flat-rotating mirror that directs light to the devices you need at the moment, and it takes less than ten minutes to switch. In the future, the telescope will be equipped with four more spectrometers and a camera for observing exoplanets. According to current plans, one additional complex will be added every two and a half years. GMT and E-ELT will also have an extremely rich instrumentation.
Supergiant E-ELT will be the world's largest telescope with a 39.3 m primary mirror. It will be equipped with a state-of-the-art adaptive optics (AO) system with three deformable mirrors capable of eliminating distortions that occur at various heights and wavefront sensors for light analysis from three natural reference stars and four to six artificial ones (generated in the atmosphere using lasers). Thanks to this system, the resolution of the telescope in the near infrared zone under the optimal state of the atmosphere will reach six arc milliseconds and come close to diffraction limit due to the wave nature of light.
European giant
The supertelescopes of the next decade will not come cheap. The exact amount is still unknown, but it is already clear that their total cost will exceed $ 3 billion. What will these gigantic tools give to the science of the Universe?
“The E-ELT will be used for astronomical observations on a wide range of scales, from the solar system to deep space. And on each scale scale, exceptionally rich information is expected from him, much of which other supertelescopes cannot give out, ”Johan Liske, a member of the scientific team of the European giant, who is engaged in extragalactic astronomy and observational cosmology, told Popular Mechanics. “There are two reasons for this: firstly, the E-ELT will be able to collect much more light than its competitors, and secondly, its resolution will be much higher. Take, say, extrasolar planets. Their list is growing rapidly, by the end of the first half of this year it contained about 2000 titles. Now the main task is not to multiply the number of discovered exoplanets, but to collect specific data about their nature. This is exactly what E-ELT will do. In particular, its spectroscopic equipment will make it possible to study the atmospheres of stony Earth-like planets with a completeness and accuracy that is completely inaccessible to currently operating telescopes. This research program provides for the search for water vapor, oxygen and organic molecules, which may be the waste products of terrestrial-type organisms. There is no doubt that E-ELT will increase the number of contenders for the role of habitable exoplanets.”
The new telescope also promises other breakthroughs in astronomy, astrophysics and cosmology. As is known, there are considerable grounds for the assumption that the Universe has been expanding for several billion years with an acceleration due to dark energy. The magnitude of this acceleration can be determined from changes in the dynamics of the redshift of light from distant galaxies. According to current estimates, this shift corresponds to 10 cm/s per decade. This value is extremely small for measurements with current telescopes, but for the E-ELT such a task is quite capable. Its ultra-sensitive spectrographs will also provide more reliable data to answer the question of whether the fundamental physical constants are constant or whether they change over time.
E-ELT promises a genuine revolution in extragalactic astronomy, which deals with objects located outside Milky Way. Current telescopes make it possible to observe individual stars in nearby galaxies, but at long distances they fail. The European Super Telescope will provide the opportunity to see the most bright stars in galaxies millions and tens of millions of light-years distant from the Sun. On the other hand, it will be able to receive light from the earliest galaxies, about which practically nothing is known yet. It will also be able to observe the stars near the supermassive black hole at the center of our Galaxy - not only to measure their speeds to within 1 km/s, but also to discover now unknown stars in the immediate vicinity of the hole, where their orbital speeds approach 10% of the speed of light. . And this, as Johan Liske says, is far from a complete list of the unique capabilities of the telescope.
Magellan telescope
The giant Magellan telescope is being built by an international consortium that brings together more than a dozen different universities and research institutes USA, Australia and South Korea. Dennis Zaritsky, professor of astronomy at the University of Arizona and deputy director of the Stewart Observatory, explained to PM that Gregorian optics was chosen because it improves image quality over a wide field of view. This optical design is last years has proven itself well on several optical telescopes in the 6-8-meter range, and even earlier it was used on large radio telescopes.
Despite the fact that GMT is inferior to TMT and E-ELT in terms of diameter and, accordingly, the area of the light-collecting surface, it has many serious advantages. Its equipment will be able to simultaneously measure the spectra of a large number of objects, which is extremely important for survey observations. In addition, GMT optics provide very high contrast and the ability to reach far into the infrared. The diameter of its field of view, like that of TMT, will be 20 arc minutes.
According to Professor Zaritsky, GMT will take its rightful place in the triad of future supertelescopes. For example, with its help it will be possible to obtain information about dark matter, the main component of many galaxies. Its distribution in space can be judged by the motion of the stars. However, most of the galaxies where it dominates contain relatively few stars, and rather dim ones at that. GMT equipment will be able to track the movements of many more such stars than the instruments of any of the currently operating telescopes. Therefore, GMT will make it possible to more accurately map dark matter, and this, in turn, will make it possible to choose the most plausible model of its particles. Such a perspective acquires special value if one considers that, so far, dark matter has not been detected either by passive detection or obtained at an accelerator. Other research programs will also be carried out at GMT: the search for exoplanets, including terrestrial planets, the observation of the most ancient galaxies, and the study of interstellar matter.
On earth and in heaven
In October 2018, the James Webb Telescope (JWST) is scheduled to be launched into space. It will work only in the orange and red zones of the visible spectrum, but it will be able to observe almost the entire mid-infrared range up to wavelengths of 28 microns (infrared rays with wavelengths over 20 microns are almost completely absorbed in the lower atmosphere by carbon dioxide and water molecules). , so that ground-based telescopes do not notice them). Because it will be protected from thermal interference earth's atmosphere, its spectrometric instruments will be much more sensitive than ground-based spectrographs. However, the diameter of its main mirror is 6.5 m, and therefore, thanks to adaptive optics, the angular resolution of ground-based telescopes will be several times higher. So, according to Michael Bolte, observations at the JWST and ground-based supertelescopes will complement each other perfectly. As for the prospects for a 100-meter telescope, Professor Bolte is very cautious in his assessments: “In my opinion, in the next 20–25 years it will simply not be possible to create adaptive optics systems that can effectively work in tandem with a hundred-meter mirror. Perhaps this will happen somewhere in forty years, in the second half of the century.
Hawaiian project
“TMT is the only one of the three future supertelescopes to be located in the Northern Hemisphere,” says Michael Bolte, a member of the board of directors of the Hawaiian project, professor of astronomy and astrophysics at the University of California at Santa Cruz. - However, it will be mounted not very far from the equator, at 19 degrees north latitude. Therefore, he, like other telescopes of the Mauna Kea observatory, will be able to survey the sky of both hemispheres, especially since, in terms of observation conditions, this observatory is one of the best places on the planet. In addition, TMT will work in conjunction with a group of nearby telescopes: the two 10-meter twins Keck I and Keck II (which can be considered the prototypes of TMT), as well as the 8-meter Subaru and Gemini-North. It is no coincidence that the Ritchey-Chrétien system is involved in the design of many large telescopes. It provides a good field of view and very effectively protects against both spherical and comatic aberration, which distorts images of objects that do not lie on the optical axis of the telescope. In addition, a truly magnificent adaptive optics is planned for TMT. It is clear that astronomers have good reason to expect that TMT observations will bring many remarkable discoveries.”
According to Professor Bolte, both TMT and other supertelescopes will contribute to the progress of astronomy and astrophysics, primarily by pushing back the boundaries of the Universe known to science both in space and in time. Even 35–40 years ago, the observable space was mainly limited to objects no older than 6 billion years. It is now possible to reliably observe galaxies about 13 billion years old, whose light was emitted 700 million years after the Big Bang. There are candidates for galaxies with an age of 13.4 billion years, but this has not yet been confirmed. It can be expected that TMT instruments will be able to detect light sources only slightly younger (by 100 million years) than the Universe itself.
TMT will provide astronomy and many other opportunities. The results that will be obtained on it will make it possible to clarify the dynamics of the chemical evolution of the Universe, to better understand the processes of formation of stars and planets, to deepen knowledge about the structure of our Galaxy and its nearest neighbors and, in particular, about the galactic halo. But the main thing is that TMT, like GMT and E-ELT, is likely to allow researchers to answer questions of fundamental importance that cannot now not only be correctly formulated, but even imagined. This, according to Michael Bolte, is the main value of supertelescope projects.
I was immediately reminded in the comments that it was necessary to write about the BTA-6 as well. I fulfill my wishes :-)
For many years, the world's largest telescope BTA (Large Azimuth Telescope) belonged to our country, and it was designed and built entirely using domestic technologies, demonstrating the country's leadership in the field of creating optical instruments. In the early 60s, Soviet scientists received a “special task” from the government - to create a telescope larger than that of the Americans (Hale telescope - 5 m.). It was considered that a meter more would be enough, since the Americans generally considered it pointless to create solid mirrors larger than 5 meters due to deformation under their own weight.
What is the history of the creation of this unique scientific object?
Now we find out...
By the way, the first photo is very, be sure to look at it too.
Photo 3. 
M. V. Keldysh, L. A. Artsimovich, I. M. Kopylov and others at the BTA construction site. 1966
The history of the Large Azimuthal Telescope (BTA, Karachay-Cherkessia) began on March 25, 1960, when, at the suggestion of the USSR Academy of Sciences and State Committee on defense technology, the Council of Ministers of the USSR adopted a resolution on the creation of a complex with a reflecting telescope with a main mirror with a diameter of 6 meters.
Its purpose is “the study of the structure, physical nature and evolution of extragalactic objects, a detailed study physical characteristics And chemical composition non-stationary and magnetic stars. The State Optical and Mechanical Plant named after A.I. OGPU (GOMZ), on the basis of which LOMO was soon formed, and the chief designer was Bagrat Konstantinovich Ioannisiani. BTA was the latest astronomical technique for its time, containing many truly revolutionary solutions. Since then, all large telescopes in the world have been mounted according to the brilliantly justified alt-azimuth scheme, for the first time in world practice used by our scientists in the BTA. The highest-class specialists worked on its creation, which ensured high quality giant device. For more than 30 years, BTA has been carrying out its stellar watch. This telescope is capable of distinguishing astronomical objects of the 27th magnitude. Imagine the earth is flat; and then, if someone in Japan would light a cigarette, with a telescope it could be clearly seen.
Photo 4. 
Cleaning the bottom of the pit. February 1966
After analyzing all the data, the site for the BTA telescope was a place at an altitude of 2100 meters near Mount Pastukhov, not far from the village of Zelenchukskaya, which is located in Karachay-Cherkessia - Nizhny Arkhyz.
According to the project, the azimuthal type of telescope mount was chosen. The total outer diameter of the mirror was 6.05 meters with a thickness of 65 cm, uniform over the entire area.
The assembly of the telescope structure was carried out in the LOMO room. Especially for this, a building with a height of over 50 meters was built. Cranes with a lifting capacity of 150 and 30 tons were installed inside the hull. Before starting the assembly, a special foundation was made. The assembly itself began in January 1966 and lasted more than a year and a half, until September 1967.
Photo 5. 
Construction of the foundations of the telescope and tower. April 1966
By the time the mirror blank with a diameter of 6 m was manufactured, the accumulated experience in processing large-sized optical blanks was not great. For processing a casting with a 6-meter diameter, when it was necessary to remove about 25 tons of glass from a workpiece, the existing experience turned out to be unsuitable, both because of low labor productivity and because of the real danger of the workpiece failure. Therefore, when processing a workpiece with a diameter of 6 m, it was decided to use a diamond tool.
Many of the telescope components are unique for their time, such as the main spectrograph of the telescope, which has a diameter of 2 meters, the guiding system, which includes a telescope-guide and a complex photo and television system, as well as a specialized computer for controlling the operation of the system.
Photo 6. 
Summer 1968 Delivery of telescope parts
BTA is a world-class telescope. The large light-gathering capacity of the telescope makes it possible to study the structure, physical nature and evolution of extragalactic objects, a detailed study of the physical characteristics and chemical composition of peculiar, non-stationary and magnetic stars, the study of star formation and the evolution of stars, the study of the surfaces and chemical composition of planetary atmospheres, trajectory measurements of artificial celestial bodies at large distances from the Earth and much more.
With its help, numerous unique studies of outer space were carried out: the most distant galaxies ever observed from Earth were studied, the mass of the local volume of the Universe was estimated, and many other mysteries of space were solved. Petersburg scientist Dmitry Vyshelovich, using the BTA, was looking for an answer to the question of whether the fundamental constants drift in the Universe. Based on his observations, he major discoveries. Astronomers from all over the world are lining up to make observations with the famous Russian telescope. Thanks to the BTA, domestic telescope builders and scientists have accumulated vast experience, which made it possible to open the way to new technologies for studying the Universe.
Photo 7. 
Installation of metal structures of the dome. 1968
The resolution of the telescope is 2000 times greater than the resolution of the human eye, and its radius of "vision" is 1.5 times greater than that of the largest US telescope at that time in Mount Palomar (8-9 billion light years versus 5-6, respectively ). It is no coincidence that BTA is called the “Eye of the Planet”. Its dimensions are amazing: height - 42 meters, weight - 850 tons. Thanks to the special design of hydraulic supports, the telescope seems to “float” on the thinnest oil cushion 0.1 mm thick, and a person is able to turn it around its axis without the use of equipment and additional tools.
By the Decree of the Government of March 25, 1960, the Lytkarinsky Optical Glass Plant was approved as the lead contractor for the development of a technological process for casting glass blanks of a mirror with a diameter of 6 m and for the manufacture of mirror blanks. Two new production buildings were built specially for this project. It was necessary to cast a glass blank weighing 70 tons, anneal it and carry out complex processing of all surfaces with the manufacture of 60 landing blind holes on the back side, a central hole, etc. Three years after the Government Decree was issued, a pilot production workshop was created. The task of the workshop included the installation and debugging of equipment, the development of an industrial technical process and the manufacture of a mirror blank.
Photo 8. 
A complex of search works carried out by LZOS specialists to create optimal processing modes made it possible to develop and implement a technology for manufacturing an industrial blank of the primary mirror. The processing of the workpiece was carried out for almost a year and a half. In 1963, the Kolomna Heavy Machine Tool Plant created a special carousel machine KU-158 for mirror processing. In parallel, a lot of research work was carried out on the technology and control of this unique mirror. In June 1974, the mirror was ready for certification, which was successfully completed. In June 1974, the critical stage of transporting the mirror to the observatory began. On December 30, 1975, the act of the State Interdepartmental Commission for the acceptance into operation of the Large Azimuthal Telescope was approved.
Photo 9. 
1989 Assembly of the 1-meter Zeiss-1000 telescope
Photo 10. 
Transportation of the upper part of the BTA pipe. August 1970
Today, there are new, more efficient astronomical systems with larger, including segmented, mirrors. But in terms of its parameters, our telescope is still considered one of the best in the world, so it is still in high demand among domestic and foreign scientists. Over the past years, it has undergone repeated modernization, primarily the management system has been improved. Today, observations can be made using a fiber optic connection directly from the astronomy town located in the valley.
Photo 11. 
The Soviet optical industry of those times was not designed to solve such problems, therefore, to create a 6-meter mirror, a factory was specially built in Lytkarino near Moscow on the basis of a small workshop for the manufacture of mirror reflectors.
The blank for such a mirror weighs 70 tons, the first few were “screwed up” due to haste, since they had to cool for a very long time in order not to crack. The “successful” billet cooled down for 2 years and 19 days. Then, during its grinding, 15,000 carats of diamond tools were produced and almost 30 tons of glass were “erased”. A fully finished mirror began to weigh 42 tons.
The delivery of the mirror to the Caucasus is worth a special mention .. First, a dummy of the same size and weight was sent to the destination, some adjustments were made to the route - 2 new river ports were built, 4 new bridges were built and 6 existing ones were strengthened and expanded, several hundred kilometers were laid new roads with perfect coverage.
The mechanical parts of the telescope were created at the Leningrad Optical and Mechanical Plant. The total mass of the telescope was 850 tons.
Photo 12. 
But despite all efforts, the American Hale BTA-6 telescope failed to "surpass" in quality (that is, in resolution). Partly due to defects in the main mirror (the first pancake is still lumpy), partly due to the worst climatic conditions at its location.
Photo 13. 
The installation in 1978 of a new, already third mirror, significantly improved the situation, but weather remained the same. In addition, the too high sensitivity of the whole mirror to minor temperature fluctuations complicates the work. "Does not see" - this is of course loudly said, until 1993 BTA-6 remained the world's largest telescope, and it is the largest in Eurasia to this day. With the new mirror, it was possible to achieve a resolution almost like that of Hale, and the “penetrating power”, that is, the ability to see faint objects, is even greater for the BTA-6 (after all, the diameter is a whole meter larger).
Photo 14. 
Photo 15. 
Photo 16. 
Photo 17. 
Photo 18. 
Over the 30-year period of the telescope's operation, its mirror was recoated several times, which led to significant damage to the surface layer, its corrosion, and, as a result, up to 70% of the mirror's reflectivity was lost. And yet, the BTA has been and remains a unique tool for astronomers, both Russian and foreign. But in order to maintain its performance and increase efficiency, it became necessary to reconstruct and update the main mirror. At present, the technology of mirror shaping and unloading, which is mastered by the specialists of JSC LZOS, makes it possible to improve its optical characteristics threefold, including the angular resolution.
Photo 19. 
Today, the technological process of shaping the surfaces of astronomical optical parts at the Lytkarino Optical Glass Plant has been brought to a new level, the achieved quality of surface shape deviations from the theoretical one has increased by an order of magnitude due to automation and modernization of production and computer control. Both the mechanical base and the technology for lightening and unloading mirrors using modern computer equipment have been significantly improved. Machines for milling, grinding and polishing a 6-meter mirror are also modernized in accordance with modern requirements. Optics controls have also been significantly improved.
The main mirror was delivered to the Lytkarino Optical Glass Plant. The milling phase has now been completed. The top layer about 8 mm thick was removed from the working surface. The mirror was transported into a thermally stabilized case and installed on an automated machine for grinding and polishing the working surface. According to the technical director - the chief engineer of the enterprise S.P. Belousov, this will be the most difficult and important stage of mirror processing - it is necessary to obtain a surface shape with much smaller deviations from the ideal paraboloid than was achieved in the seventies. After that, the telescope's mirror with resolution and penetrating power improved by an order of magnitude will be able to serve Russian and world science for at least 30 more years.
Photo 20. 
Among the specialists who participated in the manufacture of the mirror are the mechanic Zhikharev A.G., the optometrist Kaverin M.S., the locksmith Panov V.G., the milling machine Pisarenko N.I. – they are still working, passing on the rich experience of large-sized optical instrumentation to young people. Quite recently, the optician Bochmanov Yu.K., the milling machine Egorov E.V. have retired. (he re-milled the mirror last year and this year).
No one else in Russia can do such a job. In the world, besides LZOS, there are only two companies that manufacture large-sized mirrors. These are the Steward Observatory Optical Laboratory (Arizona, USA) and the SAGEM-REOSC company (France) (8 m in diameter), but even there the mirror control towers are shorter than required, since the radius of the BTA mirror is 48 meters.
BTA, or large azimuthal telescope, is the same telescope with a 6-meter 40-ton mirror, which for a long time was the largest in the world. He began his work in 1975, and thanks to him many discoveries were made. However, any mirror of any telescope needs to be updated over time, it happened here too.
When the telescope was just being built, there were no technologies in the world at all for creating a solid mirror of such a large size. So it didn't work the first time. The first piece cracked as it cooled. The second attempt ended unsuccessfully - there were too many large defects on the surface of the mirror. However, this mirror was nevertheless installed and served until 1978. And only on the third attempt the mirror turned out to be of good quality, and it was installed instead of the defective one in the same 1978. However, over time, it required resurfacing and applying a new reflective coating - its reflectivity decreased to 70%.
The work was carried out at the Lytkarino Optical Glass Plant and took 10 years. It took about a year to remove the 8mm top layer from the 6m mirror alone. Note that the accuracy of the surface of the main mirror of the telescope is a fraction of a micrometer, and this work is very fine, especially for such a huge surface.
All work on the preparation of the mirror was completed only on November 3, 2017. Then there was the problem of transporting it to the telescope. The dimensions of the container were 6.5 meters, and the coordination of the route took several months (bureaucracy in action). The mass of the tractor and the mirror was 93 tons in total, but the mirror was delivered to the observatory in 8 days.
Now the mirror will be stored in a sealed container until May, after which it will be installed on the telescope. During this time, the staff will prepare the telescope itself, especially since the mass of the updated mirror is now less due to the cameras cut into it.
However, even after the installation of the main mirror, observations of celestial objects will not begin. The mirror does not have a reflective layer, it is just transparent for now. All work on aluminizing the surface will be carried out after the installation of the mirror in the telescope. This will simplify the process, and will allow you to get the best quality surface. If you apply a reflective layer immediately, then during the transportation and installation of the mirror, it could get a lot of scratches and other damage.
And yet - the new mirror is not at all the one that has served faithfully for so many years. This is the restored first piece. And the one that is in the telescope now will be removed and placed in a container. Re-polishing and aluminizing it is too expensive a process for which the observatory simply does not have the money.
