BTA is the largest telescope in the world. The largest telescopes in the world The largest reflecting telescope in the world
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 knowledge about the cosmos around us. Today, astronomers are preparing to commission giant optical instruments with a diameter thousands of times larger.
May 26, 2015 became a real holiday for astronomers around the world. On this day, the Governor of the State of Hawaii, David Igay, allowed the start of the zero construction cycle near the top of the extinct volcano Mauna Kea 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 XXI centuries will use different optical schemes. The TMT is built according to the Ritchie-Chrétien design with a concave primary mirror and a convex secondary mirror (both hyperbolic). The E-ELT has a concave primary mirror (elliptical) and a convex secondary mirror (hyperbolic). GMT uses a Gregory 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, the TMT will see 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 made up of 492 hexagonal segments with a total area of 664 m². According to this indicator, TMT will be 80% superior to the Giant Magellan Telescope (GMT) with an aperture of 24.5 m, which will go into operation in 2021 at the Las Campanas Observatory in Chile, owned by the Carnegie Institution.
The thirty-meter telescope TMT is built according to the Ritchie-Chrétien design, which is used in many currently operating large telescopes, including the currently largest Gran Telescopio Canarias with a main mirror with a diameter of 10.4 m. At the first stage, TMT will be equipped with three IR and optical spectrometers, and in the future it is planned to add several more scientific instruments to them.
However, TMT will not remain world champion for long. The European Extremely Large Telescope (E-ELT), with a record diameter of 39.3 m, is scheduled to open in 2024 and 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 the Chilean 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 form a group of new 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. The rays reflected from the secondary mirror are directed into a 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 is implemented in many operating telescopes, in particular in the currently largest Gran Telescopio Canarias with a main mirror with a diameter of 10.4 m, in the ten-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 E-ELT optical system also contains a concave primary mirror and a convex secondary mirror, but has a number of unique features. It consists of five mirrors, and the main one is not a hyperboloid, like the 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 form a ring, the seventh is in the center). The secondary mirror is not a convex hyperboloid, as in the Ritchie-Chrétien design, 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 put into practice by Robert Hooke in 1673. According to the Gregorian scheme, the 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 Magellan telescopes with an aperture of 6.5 m, who have been working at the Las Campanas Observatory since the early 2000s.
The power is in the devices
Any telescope 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.
The TMT, which is designed to have a service life of more than 50 years, will first be equipped with three measuring instruments mounted on a common platform - IRIS, IRMS and WFOS. IRIS (InfraRed Imaging Spectrometer) is a complex of a very high-resolution video camera, providing a field of view of 34 x 34 arc seconds, and an infrared spectrometer. IRMS is a multi-slit infrared spectrometer and WFOS is a wide-field spectrometer that can simultaneously track up to 200 objects over an area of at least 25 square arcminutes. The design of the telescope includes a flat-rotating mirror that directs light to the devices needed at the moment, and switching takes less than ten minutes. 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 extremely rich instrumentation.
The supergiant E-ELT will be the world's largest telescope with a primary mirror with a diameter of 39.3 m. It will be equipped with a state-of-the-art adaptive optics (AO) system with three deformable mirrors that can eliminate distortions that occur at different 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 telescope's resolution in the near-infrared zone, under optimal atmospheric conditions, will reach six milliseconds of arc and will come very close to the diffraction limit caused by the wave nature of light.
European giant
The supertelescopes of the next decade won't 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 instruments give to the science of the Universe?
“E-ELT will be used for astronomical observations on a variety of scales - from the solar system to ultra-deep space. And at each scale scale, it is expected to provide exceptionally rich information, much of which cannot be provided by other supertelescopes,” Johan Liske, a member of the scientific team of the European giant, who is involved 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 compared to its competitors, and secondly, its resolution will be much higher. Let's take, say, extrasolar planets. Their list is growing rapidly; by the end of the first half of this year it contained about 2,000 titles. Now the main task is not to increase 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 rocky Earth-like planets with a completeness and accuracy completely inaccessible to currently operating telescopes. This research program involves searching for water vapor, oxygen and organic molecules that may be waste products of terrestrial organisms. There is no doubt that E-ELT will increase the number of candidates for the role of habitable exoplanets."
The new telescope 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 at 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 to measure using currently operating telescopes, but the E-ELT is quite capable of such a task. Its ultra-sensitive spectrographs will also provide more reliable data to answer the question of whether fundamental physical constants are constant or change over time.
E-ELT promises to revolutionize extragalactic astronomy, which deals with objects beyond the Milky Way. Current telescopes make it possible to observe individual stars in nearby galaxies, but at large distances they fail. The European supertelescope will provide the opportunity to see the brightest stars in galaxies located millions and tens of millions of light years away from the Sun. On the other hand, it will be able to receive light from the earliest galaxies, about which practically nothing is yet known. It will also be able to observe stars near the supermassive black hole at the center of our Galaxy - not only measure their speeds with an accuracy of 1 km/s, but also discover currently 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 not a complete list of the unique capabilities of the telescope.
Magellan telescope
The giant Magellan telescope is being built by an international consortium uniting more than a dozen different universities and research institutes USA, Australia and South Korea. As Dennis Zaritsky, professor of astronomy at the University of Arizona and deputy director of the Stuart Observatory, explained to PM, Gregorian optics was chosen because it improves the quality of images over a wide field of view. This optical design is recent 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, light-gathering surface area, 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 range. The diameter of its field of view, like that of the TMT, will be 20 arc minutes.
According to Professor Zaritsky, GMT will take its rightful place in the triad of future supertelescopes. For example, 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 movement of stars. However, most galaxies where it dominates contain relatively few stars, and rather dim ones. GMT equipment will be able to track the movements of many more of these 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. This prospect takes on particular value if we consider that until now dark matter has not been detected either by passive detection or obtained at an accelerator. Others will also perform on GMT research programs: search for exoplanets, including terrestrial planets, observation of the most ancient galaxies and study of interstellar matter.
On earth and in heaven
The James Webb Telescope (JWST) is scheduled to launch into space in October 2018. It will work only in the orange and red zones of the visible spectrum, but will be able to conduct observations in almost the entire mid-infrared range up to waves with a length of 28 microns (infrared rays with wavelengths above 20 microns are almost completely absorbed in the lower layer of the atmosphere by molecules of carbon dioxide and water , 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 from JWST and ground-based supertelescopes will complement each other perfectly. As for the prospects for the 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 in about forty years, in the second half of the century.”
Hawaiian project
“TMT is the only one of the three future supertelescopes for which a site has been selected in the Northern Hemisphere,” says Michael Bolte, a member of the board of directors of the Hawaiian project and a professor of astronomy and astrophysics at the University of California, Santa Cruz. “However, it will be mounted not very far from the equator, at 19 degrees north latitude. Therefore, it, like other telescopes at the Mauna Kea Observatory, will be able to survey the sky of both hemispheres, especially since this observatory is one of the best places on the planet in terms of observation conditions. In addition, the 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 prototypes of the TMT), as well as the 8-meter Subaru and Gemini-North. It is no coincidence that the Ritchie-Chrétien system is used 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. Plus, there are some truly great adaptive optics planned for the TMT. It is clear that astronomers rightly expect that observations at the TMT will yield many exciting discoveries.”
According to Professor Bolte, both TMT and other supertelescopes will contribute to the progress of astronomy and astrophysics, primarily by once again pushing back the boundaries of the known universe in both space and time. Just 35-40 years ago, 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. We can expect that TMT instruments will be able to detect light sources that are only slightly younger (100 million years) than the Universe itself.
TMT will provide astronomy and many other opportunities. The results that will be obtained from 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 closest neighbors and, in particular, about the galactic halo. But the main point is that TMT, like GMT and E-ELT, is likely to allow researchers to answer questions of fundamental importance that are currently impossible not only to formulate correctly, but even to imagine. This, according to Michael Bolte, is the main value of supertelescope projects.
The first telescope was built in 1609 by Italian astronomer Galileo Galilei. The scientist, based on rumors about the invention of the telescope by the Dutch, unraveled its structure and made a sample, which he first used for space observations. Galileo's first telescope had modest dimensions (tube length 1245 mm, lens diameter 53 mm, eyepiece 25 dioptres), an imperfect optical design and 30-fold magnification. But it made it possible to make a whole series of remarkable discoveries: discovering the four satellites of the planet Jupiter, the phases of Venus, spots on The Sun, mountains on the surface of the Moon, the presence of appendages on the disk of Saturn at two opposite points.
More than four hundred years have passed - on earth and even in space, modern telescopes are helping earthlings look into distant cosmic worlds. The larger the diameter of the telescope mirror, the more powerful the optical system.
Multi-mirror telescope
Located on Mount Hopkins, at an altitude of 2606 meters above sea level, in the state of Arizona in the USA. The diameter of the mirror of this telescope is 6.5 meters. This telescope was built back in 1979. In 2000 it was improved. It is called multi-mirror because it consists of 6 precisely adjusted segments that make up one large mirror.
Magellan telescopes
Two telescopes, Magellan-1 and Magellan-2, are located at the Las Campanas Observatory in Chile, in the mountains, at an altitude of 2400 m, the diameter of their mirrors is 6.5 m each. The telescopes began operating in 2002.
And on March 23, 2012, construction began on another more powerful Magellan telescope - the Giant Magellan Telescope; it should go into operation in 2016. In the meantime, the top of one of the mountains was demolished by the explosion to clear a place for construction. The giant telescope will consist of seven mirrors 8.4 meters each, which is equivalent to one mirror with a diameter of 24 meters, for which it has already been nicknamed “Seven Eyes”.
Separated twins Gemini telescopes
Two brother telescopes, each of which is located in a different part of the world. One - "Gemini North" stands on the top of the extinct volcano Mauna Kea in Hawaii, at an altitude of 4200 m. The other - "Gemini South", is located on Mount Serra Pachon (Chile) at an altitude of 2700 m.
Both telescopes are identical, the diameters of their mirrors are 8.1 meters, they were built in 2000 and belong to the Gemini Observatory. Telescopes are located on different hemispheres of the Earth so that the entire starry sky is accessible for observation. Telescope control systems are adapted to work via the Internet, so astronomers do not have to travel to different hemispheres of the Earth. Each of the mirrors of these telescopes is made up of 42 hexagonal fragments that have been soldered and polished. These telescopes are built with the most advanced technologies, making the Gemini Observatory one of the most advanced astronomical laboratories today.
Northern "Gemini" in Hawaii
Subaru telescope
This telescope belongs to the Japan National Astronomical Observatory. A is located in Hawaii, at an altitude of 4139 m, next to one of the Gemini telescopes. The diameter of its mirror is 8.2 meters. Subaru is equipped with the world's largest “thin” mirror: its thickness is 20 cm, its weight is 22.8 tons. This allows the use of a drive system, each of which transmits its force to the mirror, giving it an ideal surface in any position, which allows you to achieve the best image quality.
With the help of this keen telescope, the most distant galaxy known to date was discovered, located at a distance of 12.9 billion light years. years, 8 new satellites of Saturn, protoplanetary clouds photographed.
By the way, “Subaru” in Japanese means “Pleiades” - the name of this beautiful star cluster.
Japanese Subaru Telescope in Hawaii
Hobby-Eberly Telescope (NO)
Located in the USA on Mount Faulks, at an altitude of 2072 m, and belongs to the MacDonald Observatory. The diameter of its mirror is about 10 m. Despite its impressive size, Hobby-Eberle cost its creators only $13.5 million. It was possible to save the budget thanks to some design features: the mirror of this telescope is not parabolic, but spherical, not solid - it consists of 91 segments. In addition, the mirror is at a fixed angle to the horizon (55°) and can only rotate 360° around its axis. All this significantly reduces the cost of the design. This telescope specializes in spectrography and is successfully used to search for exoplanets and measure the rotation speed of space objects.
Large South African Telescope (SALT)
It belongs to the South African Astronomical Observatory and is located in South Africa, on the Karoo plateau, at an altitude of 1783 m. The dimensions of its mirror are 11x9.8 m. It is the largest in the Southern Hemisphere of our planet. And it was made in Russia, at the Lytkarino Optical Glass Plant. This telescope became an analogue of the Hobby-Eberle telescope in the USA. But it was modernized - the spherical aberration of the mirror was corrected and the field of view was increased, thanks to which, in addition to working in spectrograph mode, this telescope is capable of obtaining excellent photographs of celestial objects with high resolution.
The largest telescope in the world ()
It stands on the top of the extinct Muchachos volcano on one of the Canary Islands, at an altitude of 2396 m. Diameter of the main mirror – 10.4 m. Spain, Mexico and the USA took part in the creation of this telescope. By the way, this international project cost 176 million US dollars, of which 51% was paid by Spain.
The mirror of the Grand Canary Telescope, composed of 36 hexagonal parts, is the largest existing in the world today. Although this is the largest telescope in the world in terms of mirror size, it cannot be called the most powerful in terms of optical performance, since there are systems in the world that surpass it in their vigilance.
Located on Mount Graham, at an altitude of 3.3 km, in Arizona (USA). This telescope belongs to the Mount Graham International Observatory and was built with money from the USA, Italy and Germany. The structure is a system of two mirrors with a diameter of 8.4 meters, which in terms of light sensitivity is equivalent to one mirror with a diameter of 11.8 m. The centers of the two mirrors are located at a distance of 14.4 meters, which makes the telescope's resolving power equivalent to 22 meters, which is almost 10 times greater than that of the famous Hubble Space Telescope. Both mirrors of the Large Binocular Telescope are part of the same optical instrument and together form one huge binocular - the most powerful optical instrument in the world at the moment.
Keck I and Keck II are another pair of twin telescopes. They are located next to the Subaru telescope on the top of the Hawaiian volcano Mauna Kea (height 4139 m). The diameter of the main mirror of each of the Keks is 10 meters - each of them individually is the second largest telescope in the world after the Grand Canary. But this telescope system is superior to the Canary telescope in terms of vigilance. Parabolic mirrors These telescopes are composed of 36 segments, each of which is equipped with a special support system, computer controlled.
The Very Large Telescope is located in the Atacama Desert in the Chilean Andes, on Mount Paranal, 2635 m above sea level. And it belongs to the European Southern Observatory (ESO), which includes 9 European countries.
A system of four 8.2-meter telescopes, and another four auxiliary 1.8-meter telescopes, is equivalent in aperture to one instrument with a mirror diameter of 16.4 meters.
Each of the four telescopes can work separately, obtaining photographs in which stars up to 30th magnitude are visible. Rarely do all telescopes work at once; it is too expensive. More often, each of the large telescopes works in tandem with its 1.8-meter assistant. Each of the auxiliary telescopes can move on rails relative to its “big brother”, occupying the most advantageous position for observing a given object. The Very Large Telescope is the most advanced astronomical system in the world. A lot of astronomical discoveries were made on it, for example, the world's first direct image of an exoplanet was obtained.
Space Hubble telescope
The Hubble Space Telescope is a joint project of NASA and the European Space Agency, an automatic observatory in Earth orbit, named after the American astronomer Edwin Hubble. The diameter of its mirror is only 2.4 m, which is smaller than the largest telescopes on Earth. But due to the lack of atmospheric influence, the resolution of the telescope is 7 - 10 times greater than a similar telescope located on Earth. Hubble is responsible for many scientific discoveries: the collision of Jupiter with a comet, the image of the relief of Pluto, auroras on Jupiter and Saturn...
Hubble telescope in earth orbit
Hello, comrades. I'll tell you something, mostly wasted objects and trash heaps. Let's visit an active facility - a real astrophysical observatory with a huge telescope.
So, here it is, a special astrophysical observatory of the Russian Academy of Sciences, known as object code 115.
It is located in the North Caucasus at the foot of Mount Pastukhovaya in the Zelenchuk region of the Karachay-Cherkess Republic of Russia (Nizhny Arkhyz village and Zelenchukskaya village). Currently, the observatory is the largest Russian astronomical center for ground-based observations of the Universe, which has large telescopes: the six-meter optical reflector BTA and the RATAN-600 ring radio telescope. Founded in June 1966. 
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This gantry crane was used to build the observatory.
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For more details, you can read http://www.sao.ru/hq/sekbta/40_SAO/SAO_40/SAO_40.htm here. 
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The observatory was created as a center for collective use to ensure work optical telescope BTA (Large Azimuth Telescope) with a mirror diameter of 6 meters and the RATAN-600 radio telescope with a ring antenna diameter of 600 meters, then the world's largest astronomical instruments. They were commissioned in 1975-1977 and are designed to study objects in near and deep space using ground-based astronomy methods. 
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Looking at this futuristic door you just want to go inside and feel all the power. 
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Here we are inside. 
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We have an old control panel in front of us. Apparently it doesn't work. 
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Here comes the most interesting part. BTA - "Large Azimuth Telescope". This marvel has been the largest telescope in the world since 1975, when it surpassed Palomar Observatory's 5-meter Hale Telescope, until 1993, when the Keck Telescope with a 10-meter segmented mirror became operational.
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Yes, 
this same Keck.
The BTA is a reflecting telescope. The main mirror with a diameter of 605 cm has the shape of a paraboloid of revolution. The focal length of the mirror is 24 meters, the weight of the mirror excluding the frame is 42 tons. The optical design of the BTA provides for operation in the main focus of the main mirror and two Nesmith focuses. In both cases, an aberration corrector can be used.
The telescope is mounted on an alt-azimuth mount. The mass of the moving part of the telescope is about 650 tons. The total mass of the telescope is about 850 tons.
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Chief designer - Doctor of Technical Sciences Bagrat Konstantinovich Ioannisiani (LOMO). 
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The optical system of the telescope was manufactured at the Leningrad Optical-Mechanical Association named after. V.I. Lenin (LOMO), Lytkarino Optical Glass Plant (LZOS), State Optical Institute named after. S. I. Vavilova (GOI).
For its production, even separate workshops were built that had no analogues.
Do you know what?
- The blank for the mirror, cast in 1964, cooled for more than two years.
- To process the workpiece, 12,000 carats of natural diamonds in powder form were used; processing with a grinding machine manufactured at the Kolomna Heavy Machine Tool Plant took 1.5 years.
- The mass of the blank for the mirror was 42 tons.
- In total, the creation of a unique mirror lasted for 10 years.
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The main mirror of the telescope is subject to thermal deformation, like all huge telescopes of this type. If the temperature of the mirror changes faster than 2° per day, the resolution of the telescope drops by one and a half times. Therefore, special air conditioners are installed inside to maintain optimal temperature conditions. It is forbidden to open the telescope dome if the temperature difference between the outside and inside of the tower is more than 10°, since such temperature changes can lead to destruction of the mirror. 
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Plumb 
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Unfortunately, the North Caucasus is not the best place for such a mega-device. The fact is that in mountains open to all winds there is very high atmospheric turbulence, which significantly impairs visibility and does not allow using the full power of this telescope. 
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On May 11, 2007, transportation of the first main mirror of the BTA began to the Lytkarino Optical Glass Plant (LZOS), which manufactured it, for the purpose of deep modernization. The telescope now has a second primary mirror installed. After processing in Lytkarino - removing 8 millimeters of glass from the surface and repolishing, the telescope should be among the ten most accurate in the world. The modernization was completed in November 2017. Installation and start of research are planned for 2018. 
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I hope you enjoyed the walk. Let's go out. 
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Designed using "
What can you see through a telescope?
One of the most common questions is: “What can you see with a telescope?” With the right approach and choice of device, you can see many interesting objects in the sky. The visibility of space objects depends on the diameter of the lens. The larger the diameter, the more light the telescope will collect from the object, and the finer details we will be able to discern.
Consider your options. These photographs were taken under ideal viewing conditions. And it is worth noting that the human eye perceives colors differently.
1. What can be seen with a 60-70 mm or 70-80 mm telescope
These devices are the most popular among beginners. Most of them can also be used as a spotting scope for ground objects.
With their help you can see many objects in the sky, for example, craters on the Moon with a diameter of 8 km, sunspots (only with an aperture filter), four moons of Jupiter, phases of Venus, craters of the Moon with a diameter of 7-10 km, cloud bands on Jupiter and 4 its satellite, the rings of Saturn.
Photos of objects taken with a telescope with a diameter of 60-80 mm:
List of recommended telescopes with lens diameters of 60, 70, 80 mm:
2. What can be seen in a telescope: refractor 80-90 mm, reflector 100-120 mm, catadioptric 90-125 mm
In telescopes with this diameter, you will see lunar craters about 5 km in size, sunspot structure, granulation and flare fields. Always use a sun filter! Mars will be visible as a small circle. You can also see the Cassini gap in the rings of Saturn and 4-5 satellites, the Great Red Spot (GRS) on Jupiter, etc.
Photos of objects taken with a telescope with this lens diameter:
List of recommended telescopes with lens diameters 80, 90, 100-125 mm:
3. What can be seen in a telescope: refractor 100-130 mm, reflector or catadioptric 127-150 mm.
These models will allow you to examine space in more detail. With this diameter you can achieve significant success in astronomy and see:
4. What can be seen in a telescope: refractor 150-180 mm, reflector or catadioptric 127-150 mm
It is better to use them only for suburban observations, since using them in urban conditions will interfere with the full potential of the aperture due to excess urban illumination. Refractors of these diameters are quite difficult to find, because their cost is significantly higher than reflectors and mirror-lens telescopes with the same parameters.
With their help you can see double stars with a separation of less than 1″, faint stars up to 14 stars. magnitude, lunar formations 2 km in size, 6-7 satellites of Saturn and other space objects.
Photos of objects taken with a telescope with a given diameter:
I was immediately reminded in the comments that I should definitely write about BTA-6. I fulfill your wishes :-)
For many years, the world's largest telescope, BTA (Large Azimuthal 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 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 in size 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 from a very good one, be sure to look at it too.
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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 proposal of the USSR Academy of Sciences and the State Committee for Defense Equipment, the USSR Council of Ministers 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 “to study the structure, physical nature and evolution of extragalactic objects, a detailed study of the physical characteristics and chemical composition nonstationary and magnetic stars." The State Optical-Mechanical Plant named after. OGPU (GOMZ), on the basis of which LOMO was soon formed, and the chief designer was Bagrat Konstantinovich Ioannisiani. The BTA was the latest astronomical technology for its time, containing many truly revolutionary solutions. Since then, all large telescopes in the world have been mounted using the brilliantly proven alt-azimuth scheme, which was used for the first time in world practice by our scientists at BTA. The highest-class specialists worked on its creation, which ensured the high quality of the giant device. For more than 30 years now, BTA has been keeping 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 were to light a cigarette, with the help of a telescope it could be clearly seen.
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Cleaning the bottom of the pit. February 1966
After analyzing all the data, the site for the BTA telescope became 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 telescope structure was assembled in the LOMO premises. A building over 50 meters high was built especially for this purpose. Cranes with a lifting capacity of 150 and 30 tons were installed inside the hull. Before assembly began, a special foundation was made. The assembly itself began in January 1966 and lasted more than a year and a half, until September 1967.
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Construction of telescope and tower foundations. 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 limited. For processing a casting with a 6-meter diameter, when it was necessary to remove about 25 tons of glass from the workpiece, the existing experience turned out to be unsuitable, both due to 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's components are unique for its time, such as the main spectrograph of the telescope, which has a diameter of 2 meters, a guiding system, which includes a guide telescope and a complex photo and television system, as well as a specialized computer for controlling the operation of the system
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Summer 1968 Delivery of telescope parts
BTA is a world-class telescope. The large light-gathering ability 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, study of the processes of star formation and evolution of stars, study of the surfaces and chemical composition of the atmospheres of planets, trajectory measurements of artificial celestial bodies at great 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. St. Petersburg scientist Dmitry Vyshelovich, with the help of the BTA, sought an answer to the question of whether fundamental constants drift in the Universe. Based on the results of his observations, he made the most important discoveries. Astronomers from all over the world are lining up to make observations using the famous Russian telescope. Thanks to the BTA, domestic telescope builders and scientists have accumulated vast experience, which has made it possible to open the way to new technologies for studying the Universe.
Photo 7. 
Installation of dome metal structures. 1968
The resolving power 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 at 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 the hydraulic supports, the telescope seems to “float” on a thin oil cushion 0.1 mm thick, and a person is able to rotate it around its axis without the use of equipment or additional tools.
By Government Decree of March 25, 1960, the Lytkarino Optical Glass Plant was approved as the lead contractor for the development of a technological process for casting a mirror blank with a diameter of 6 m from glass and for the production of a mirror blank. Two new production buildings were built specifically 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 production of 60 mounting 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 workshop's tasks included installation and debugging of equipment, development of an industrial technical process and production of a mirror blank.
Photo 8. 
A set 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 for the main mirror. Processing of the workpiece was carried out for almost a year and a half. To process mirrors, the Kolomna Heavy Machine Tool Plant created a special rotary machine KU-158 in 1963. At the same time, extensive 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 crucial stage of transporting the mirror to the observatory began. On December 30, 1975, the act of the State Interdepartmental Commission on the acceptance into operation of the Large Azimuth 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, which is why it is still in high demand among domestic and foreign scientists. Over the past years, it has undergone repeated modernization, primarily improving the management system. Today, observations can be made using a fiber-optic connection directly from the astronomer town located in the valley.
Photo 11. 
The Soviet optical industry of those times was not designed to solve such problems, so to create a 6-meter mirror, a plant was specially built in Lytkarino near Moscow on the basis of a small workshop for the production of mirror reflectors.
The blank for such a mirror weighs 70 tons, the first few were “screwed up” due to haste, since in order not to crack they had to cool for a very long time. The “successful” billet cooled for 2 years and 19 days. Then, during its polishing, 15,000 carats of diamond tools were produced and almost 30 tons of glass were “erased.” The 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 its destination, some adjustments were made to the route - 2 new river ports were built, 4 new bridges and 6 existing ones were strengthened and expanded, several hundred kilometers were laid new roads with perfect surface.
The mechanical parts of the telescope were created at the Leningrad Optical-Mechanical Plant. The total mass of the telescope was 850 tons.
Photo 12. 
But despite all efforts, it was not possible to “outdo” the American Hale telescope BTA-6 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 of a new, third mirror in 1978 significantly improved the situation, but the weather conditions remained the same. In addition, the work is complicated by the too high sensitivity of the solid mirror to minor temperature fluctuations. “Does not see” - this is, of course, said loudly; until 1993, BTA-6 remained the world’s largest telescope, and it remains the largest in Eurasia to this day. With the new mirror, it was possible to achieve a resolution almost like that of the Hale, and the “penetrating power,” that is, the ability to see faint objects, is even greater in the BTA-6 (after all, the diameter is a whole meter larger).
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Photo 18. 
Over the 30-year period of operation of the telescope, 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 reflective ability of the mirror was lost. And yet, the BTA was and remains a unique tool for astronomers, both Russian and foreign. But to maintain its performance and increase efficiency, it became necessary to reconstruct and update the main mirror. Currently, the technology of shaping and unloading the mirror, which is owned by the specialists of JSC LZOS, makes it possible to triple its optical characteristics, including angular resolution.
Photo 19. 
Today process The shaping of 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 has increased by an order of magnitude due to automation and modernization of production and computer control. Both the mechanical base and the technology of lightening and unloading mirrors using modern computer equipment have improved significantly. The machines for milling, grinding and polishing the 6-meter mirror have also been modernized in accordance with modern requirements. Optical controls have also been significantly improved.
The main mirror was delivered to the Lytkarino Optical Glass Plant. The milling stage has now been completed. The top layer about 8 mm thick was removed from the working surface. The mirror is transported into a heat-stabilized case and installed on an automated machine for grinding and polishing the working surface. According to the technical director - chief engineer of the enterprise S.P. Belousov, this will be the most difficult and critical 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 this, the telescope mirror, with its resolution and penetrating power improved by an order of magnitude, will be able to serve Russian and world science for at least another 30 years.
Photo 20. 
Among the specialists who participated in the manufacture of the mirror are mechanic Zhikharev A.G., optician Kaverin M.S., mechanic Panov V.G., milling machine operator Pisarenko N.I. – they are still working today, passing on their rich experience in large-scale optical instrument making to young people. Just recently, optician Yu.K. Bochmanov and milling machine operator E.V. Egorov retired. (he did the mirror re-milling last year and this year).
No one else in Russia can do this kind of work. In the world, besides LZOS, there are only two companies that produce 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.