The Astronomical Telescope is an important instrument for observing celestial bodies, and it is no exaggeration to say that without the birth and development of telescopes, there would be no modern astronomy. With the improvement and improvement of telescope performance in all aspects, astronomy is also experiencing a huge leap, rapidly advancing human understanding of the universe.
Usually there are two mirrors on a telescope. The small one is called the starfinder, which is used to find objects, also called the sight. Eyepiece are separate individuals, is to determine the magnification, eyepiece will have on the F value, this is the focal length of the eyepiece, divide the F value of the primary mirror by the current of the eyepiece used F value, is the current magnification, remember, magnification is a standard, the limit of 6 cm diameter telescope magnification is about 120 times, the ratio of maximum 8 cm around 160 times.
The telescope's ability to collect light increases with the aperture, and the more powerful the telescope's ability to collect light, the darker and farther objects can be seen, which is actually able to see the earlier universe. The development of astrophysics required larger telescopes.
But as the size of the telescope grew, a series of technical problems ensued. The hale lens weighs 14.5 tons, the movable part weighs 530 tons, and the 5-meter mirror weighs 800 tons. On the one hand, the excessive gravity of the telescope will make the lens deformation quite obvious; on the other hand, the non-uniform temperature of the lens will also distort the mirrors, which will affect the image quality. In manufacturing terms, the cost of conventional methods of making telescopes is almost directly proportional to the square or square of the aperture, so larger telescopes have to be made new.
Since the 1970s, many new technologies have been developed in the field of telescope manufacturing, including optics, mechanics, computers, automatic control and precision machinery. These technologies enable the manufacture of the telescope to break through the limitations of mirror aperture, and reduce the cost and simplify the structure of the telescope; In particular, the appearance and application of active optical technology has made a leap in the design of the telescope.
Since the eighties, there has been an international boom in the manufacture of a new generation of large telescopes. Among them, the main mirror of VLT of European southern observatory, GEMINI of America, Britain and Canada, SUBARU of Japan adopts thin mirror. The primary mirrors of the KeckI, KeckII and HET telescopes in the United States are spliced.
Good conventional telescopes, such as cassegrain focus, can concentrate 80% of their geometrical light in a range of 0.6 "under the best working conditions, while newer large telescopes made with new technology can keep 80% of their light in a range of 0.2" ~0.4 "or better.
Here are some typical large telescopes:
The KeckI (KeckII) KeckI and KeckII, built in 1991 and 1996 respectively, are the largest optical telescopes in operation in the world today, named for their funding, largely donated by entrepreneur KeckWM ($94 million for KeckII, $74.6 million for KeckII). Both identical telescopes are located in mauna kea, Hawaii, and are put together for interference observation.
All of them have a diameter of 10 meters and are composed of 36 hexagonal mirror splices. Each of them has a diameter of 1.8 meters and a thickness of only 10 centimeters. With the active optical support system, the mirror can maintain a high accuracy. There are three focal plane devices: near infrared camera, high resolution CCD detector and high dispersion spectrometer.
"A large telescope like Keck allows us to trace the origins of the universe along the river of time, and Keck allows us to see the first moments of the universe."
Europe is great
The European southern observatory (eso) has been developing four 8-meter caliber telescopes since 1986 to form an optical telescope (VLT) with an equivalent diameter of 16 meters. These four 8-meter telescopes are arranged in a straight line. They are all RC optical systems with a focal ratio of F/2 and are supported by ground horizon devices. The primary mirror is supported by active optical systems with a pointing accuracy of 1 "and tracking accuracy of 0.05". These four telescopes can form an interference array to do two interference observations, or each telescope can be used alone.
GEMINI is an international facility dominated by the United States (50 percent in the United States, 25 percent in the United Kingdom, 15 percent in Canada, 5 percent in Chile, 2.5 percent in Argentina, and 2.5 percent in Brazil), administered by the United States university consortium (AURA). It consists of two eight-meter telescopes, one in the northern hemisphere and the other in the southern hemisphere, for a round-the-clock systematic observation. The primary mirror is controlled by active optics, the secondary mirror is used as tilting mirror to correct quickly, and the infrared region will be close to the diffraction limit through the adaptive optics system.
The project started in September 1993, with the first one in Hawaii in July 1998 and the second one in Chile in September 2000. The whole system is expected to be put into operation after acceptance in 2001.
The Pleiades cluster
This is an 8-meter optical/infrared telescope (SUBARU). It has three characteristics: first, the mirror is thin, through active optics and adaptive optics to obtain high image quality; Second, it can realize high-precision tracking of 0.1 ". Third, the cylindrical observation chamber is used to automatically control the ventilation and air filters, so that the removal of thermal turbulence to the best conditions. The telescope USES Serrurier truss to keep the primary frame parallel to the secondary frame in motion. Belonging to the Japanese astronomical society, located in Hawaii, USA.
LAMOST (guo shoujing), the multi-objective optical fiber spectrum telescope of the greater sky region, is a reflective schmidt telescope built in China with an effective optical aperture of 4 meters, a focal length of 20 meters and a field of view of 20 square degrees. Its technical features are:
1. The active optics technology is applied to the schmidt system of reflection, and the spherical aberration correction is made in the tracking celestial body motion.
2. Splicing technique is used for both spherical master mirror and reflector.
3. The spectrum of multi-target optical fibers (up to 4,000, compared with 600 for a typical telescope) would be an important breakthrough.
LAMOST pushed the general measured galaxy limit magnitude to 20.5m, about 2 higher than the SDSS plan, and achieved the universal spectral survey of 107 galaxies, increasing the number of observation targets by 1 order of magnitude.
In 1932, jansky.k.g used a radio antenna to detect radio radiation from the center of the Milky Way galaxy (in the direction of the constellation Sagittarius), marking the opening of the first window for observation outside the traditional optical band.
After the second world war, radio astronomy stood out, and the radio telescope played a key role in the development of radio astronomy. For example, the four major discoveries of astronomy in the sixties, quasars, pulsars, interstellar molecules and cosmic microwave background radiation, were all observed by radio telescopes. Every step forward in the development of radio telescopes is without exception a milestone in the development of radio astronomy.
In 1946, the university of Manchester in the United Kingdom built a fixed parabolic radio telescope with a diameter of 66.5 meters. In 1955, the world's largest rotating parabolic radio telescope was built. In the 1960s, the United States built the world's largest single-aperture radio telescope in arecibo, Puerto Rico, with a diameter of 305 meters.
In 1962, Ryle invented the integrated aperture radio telescope, which won him the 1974 Nobel Prize in physics. The integrated aperture radio telescope realizes the effect of multiple small antenna structures to obtain single antennas of the same size.
In 1967, Broten et al. first recorded the VLBI interference fringes.
In the 1970s, the federal republic of Germany built near boen an omnidirectional rotating parabolic radio telescope 100 meters in diameter, the world's largest rotating single-antenna radio telescope.
Since the 1980s, the VLBI network (EVN) in Europe, the VLBA array in the United States and the space VLBI (VSOP) in Japan have been put into use successively. This is the representative of the new generation of radio telescopes, which have greatly exceeded the previous ones in sensitivity, resolution and observation band.
Shanghai astronomical observatory and urumqi station, Chinese academy of sciences, the two 25 m radio telescope, as a formal member joined the U.S. earth rotation and continuous observation plan (CORE) and European network (EVN) very long baseline interference, the two plans were used in the study of the earth's rotation and high precision astrometry (CORE) and astrophysics research (EVN). This method of joint long baseline interferometry by national radio telescopes has the effect that no single country can achieve with a large telescope alone.
In addition, the 100 meter single-antenna telescope (GBT) developed by the national four observatories of the United States (NARO) takes the largest infrared astronomy telescope
Largest infrared astronomy telescope
The antenna is currently being installed with no occlusion (bias feedback), active optics and other designs and may be put into use by the year 2000.
The international joint development of the low-frequency radio telescope array (SKA) with a receiving area of 1 square kilometer will increase the sensitivity of low-frequency radio observations by about two orders of magnitude, and various preliminary studies are being carried out in the countries concerned.
In addition to increasing radio frequency band coverage, the smithsonian astrophysical observatory and the Taiwan institute of astronomy and astrophysics of China are building the first international submillimeter wave interferometer array (SMA) in Hawaii, which consists of eight 6-meter antennas with operating frequencies from 190GHz to 85z, and some equipment has been installed. The MMA in the United States and LAS in Europe will merge into a new MMA plan, ALMA. The project will consist of 64 12m antennas, with the longest baseline reaching more than 10km and operating frequencies ranging from 70 to 950GHz, located near Atacama in Chile, and construction will begin in 2001 if the merger goes well, with the Japanese side also considering the possibility of participating in the scheme.
In order to improve the Angle resolution of radio observation, most of the new generation of large equipment consider the scheme of interference array. In order to further improve the angular resolution and sensitivity of spatial VLBI observations, the second generation spatial VLBI project - ARISE (25-meter aperture) has been proposed.
It is believed that the completion and use of these devices will make radio astronomy an important research tool for astronomy and bring unpredictable opportunities for the development of astronomy.
The construction project of the world's largest aperture spherical radio telescope realizes the successful closure of ring beams in pingtang county, buyi and miao autonomous prefecture, guizhou province. The telescope is 500 meters in diameter and covers about the size of 30 football fields. The foundation of the project was laid on December 26, 2008, and it is expected to be completed in September, 2016.  a new radio telescope is reported to be the world's first. In accordance with the requirements of science, super telescopes will produce electromagnetic waves, which have an impact on human health. Residents should migrate 5 kilometers away. At present, the local government has started to move matters, to move residents economic compensation and housing assistance. According to the report, the guizhou provincial reservoir and ecological immigration bureau provided subsidies of 12,000 yuan per person. According to the standard of 10,000 yuan per household, the provincial commission of minzong of guizhou province provides subsidies to households with housing difficulties for ethnic minorities. 
When completed, the telescope will be the world's largest radio telescope, far exceeding the 100 meters in Bonn, Germany, and the 300 meters in Arecibo, the United States, and will remain a world-class facility for the next 20 to 30 years.