Modern large astronomical telescope

The light collecting ability of telescope increases with the increase of aperture. The stronger the telescope's light collection ability, the darker and farther the celestial body can be seen, which is actually to see the earlier universe. The development of astrophysics requires a telescope with a larger aperture.

However, with the increase of telescope aperture, a series of technical problems have followed. The lens weight of Haier telescope is 14.5 tons, the movable part is 530 tons, and the 5-meter mirror is 800 tons. On the one hand, the excessive weight of the telescope will obviously deform the lens, on the other hand, the uneven temperature of the mirror body will also deform the mirror surface, which will affect the imaging quality. From the manufacturing point of view, the cost of traditional methods to manufacture telescopes is almost proportional to the square or cube of aperture, so it is necessary to find a new method to manufacture telescopes with larger aperture.

Since 1970s, many new technologies have been developed in manufacturing telescopes, involving optics, machinery, computers, automatic control and precision machinery. These technologies make the manufacture of telescope break through the limitation of mirror aperture, reduce the cost and simplify the structure of telescope. In particular, the emergence and application of active optical technology has made a leap in the design concept of telescopes.

Since the 1980s, there has been an international upsurge in manufacturing a new generation of large telescopes. Among them, VLT of the European Southern Observatory, Gemini of the United States, Britain and Canada, and Subaru of Japan all used thin mirrors as primary mirrors; The primary mirrors of KeckI, KeckII and HET telescopes in the United States adopt splicing technology.

The excellent Seglin focus of the traditional telescope can concentrate 80% of the geometric light energy in the range of 0.6 "under the best working condition, while the new generation of large telescopes manufactured by new technology can concentrate 80% of the light energy in the range of 0.2" ~ 0.4 ",or even better.

Here are a few representative large telescopes: KeckI and KeckII were built in 199 1 and 1996 respectively, which are the largest optical telescopes that have been put into operation in the world at present, because their funds are mainly donated by entrepreneur KeckWM (KeckI is 90. These two identical telescopes were placed in Monaque, and they were put together for interference observation.

Their aperture is 10 meter, and they are composed of 36 hexagonal mirrors. The aperture of each mirror is1.8m, and the thickness is only10cm. Through the active optical support system, the mirror maintains extremely high accuracy. There are three focal plane devices: near infrared camera, high resolution CCD detector and high dispersion spectrometer.

Large telescopes like Keck can let us explore the origin of the universe along the long river of time, and Keck can let us see the moment when the universe was first born. Gemini telescope is an international equipment dominated by the United States (50% in the United States, 25% in the United Kingdom, 0/5% in Canada/KLOC, 5% in Chile, 2.5% in Argentina and 2.5% in Brazil), which is realized by AURA. It consists of two 8-meter telescopes, one in the northern hemisphere and the other in the southern hemisphere, for all-day systematic observation. The primary mirror is controlled by active optics, and the secondary mirror is quickly corrected by tilting the mirror. Through the adaptive optical system, the infrared region will approach the diffraction limit.

The project started in September. 1993. The first one was launched in Hawaii in July, 1998, and the second one was launched in serapa Qiongtai site in Chile in September 2000. The whole system is expected to be put into use after acceptance in 200 1 year. This is an 8m optical/infrared telescope (Subaru). It has three characteristics: first, the mirror is thin, and high imaging quality is obtained through active optics and adaptive optics; Second, it can realize high-precision tracking of 0. 1 "; Thirdly, a cylindrical observation room is adopted to automatically control ventilation and air filters, so as to eliminate thermal turbulence to the best state. This telescope adopts Serrurier truss, which can keep the main frame and the auxiliary frame parallel when moving. It belongs to the Japanese Astronomical Society and is located in Hawaii, USA.

LAMOST (Guo Shoujing) multi-target optical fiber spectrum telescope is a reflective Schmidt telescope for the ceremony of medium satellite, which has been built in China with an effective aperture of 4m, a focal length of 20m and a field of view of 20 square degrees. Its technical characteristics are as follows:

1. The active optics technology is applied to the reflective Schmidt system, and the spherical aberration is corrected in real time when tracking the motion of celestial bodies, thus realizing two functions of large aperture and large field of view.

2. Both the spherical primary mirror and the reflector adopt splicing technology.

3. The spectral technology of multi-target optical fibers (as many as 4,000, compared with only 600 in general telescopes) will be an important breakthrough.

LAMOST pushed the limit magnitude of galaxies in the census to 20.5m, which was about 2 times higher than the SDSS plan. The census of 107 galaxies was realized, and the observation targets of 1 were increased. At 1932, Jansky. K g detected the radio emission from the center of the Milky Way (Sagittarius direction) with a radio antenna, which marked the first observation window for human beings outside the traditional optical band.

After World War II, radio astronomy appeared, and radio telescopes played a key role in the development of radio astronomy. For example, the four major discoveries of astronomy in the 1960s, quasars, pulsars, interstellar molecules and cosmic microwave background radiation, were all observed through radio telescopes. Every major progress of radio telescope, without exception, will set a milestone for the development of radio astronomy.

The University of Manchester in England built a fixed parabolic radio telescope with a diameter of 66.5 meters in 1946, and the world's largest rotatable parabolic radio telescope in 1955. In 1960s, the United States built a parabolic radio telescope with a diameter of 305 meters in Arecibo, Puerto Rico. It is fixed on the ground along the hillside and cannot rotate. It is the largest single aperture radio telescope in the world.

1962, Ryle invented the synthetic aperture radio telescope, and thus won the 1974 Nobel Prize in physics. Synthetic aperture radio telescope achieves the effect of a large aperture single antenna plus several smaller antenna structures.

1967 Broten et al. recorded VLBI interference fringes for the first time.

In 1970s, the Federal Republic of Germany built an omnidirectional rotating parabolic radio telescope with a diameter of 100 m near Born, which is the largest rotatable single antenna radio telescope in the world.

Since 1980s, Europe's VLBI network (EVN), America's VLBA array and Japan's space VLBI(VSOP) have been put into use one after another. They are the representatives of a new generation of radio telescopes, which greatly surpass previous telescopes in sensitivity, resolution and observation band.

As full members, two 25m radio telescopes from Shanghai Observatory and Urumqi Astronomical Station of Chinese Academy of Sciences participated in the continuous observation program of the Earth's rotation (CORE) in the United States and the very long baseline interferometer network (EVN) in Europe, which were used for the Earth's rotation, high-precision astrometric research (CORE) and astrophysical research (EVN) respectively. This way of long baseline interference observation by radio telescopes in various countries has achieved the effect that no country can achieve by using large telescopes alone.

In addition, the 100m single-antenna telescope (GBT) developed by the National Four Astronomical Observatories (NARO) of the United States adopts the design of unshielded (biased feed) and active optics. The antenna is currently being installed and may be put into use in 2000.

The low-frequency radio telescope array (SKA) with a receiving area of 1 km2 will be jointly developed internationally. This plan will improve the sensitivity of low-frequency radio observation by about two orders of magnitude, and relevant countries are carrying out various pre-studies.

In terms of increasing the coverage of radio observation bands, the Smithsonian Astrophysics Observatory of the United States and the Institute of Astronomy and Astrophysics of Taiwan Province Province of China are building the first submillimeter wave interference array (SMA) in Hawaii, which consists of eight 6-meter antennas, and its working frequency ranges from 190GHz to 85z, and some equipment has been installed. The millimeter wave array (MMA) in the United States and the Great Southern Sky Array (LAS) in Europe will be merged into a new millimeter wave array plan-ALMA. The project will include 64 12m antennas, with the longest baseline exceeding 10km and the operating frequency ranging from 70 to 950GHz. If the merger is successful, construction will start on 200 1, and Japan is also considering the possibility of participating in this project.

In improving the angular resolution of radio observation, most of the new generation of large-scale equipment consider the scheme of interference array; In order to further improve the angular resolution and sensitivity of space VLBI observation, the second generation space VLBI project-25m aperture is proposed.

It is believed that the completion and use of these devices will make radio astronomy an important research means of astronomy and bring unpredictable opportunities for the development of astronomy. The world's largest spherical radio telescope construction project has successfully closed the ring beam in Pingtang County, Qiannan Buyi and Miao Autonomous Prefecture, Guizhou Province. The telescope is 500 meters in diameter and covers an area of about 30 football fields. The foundation stone was laid on February 26th, 2008, and it is expected to be completed in September 2006. It is reported that the new radio astronomical telescope will be the first in the world. According to scientific requirements, the super astronomical telescope will produce electromagnetic waves, which will have an impact on human health. Residents should move 5 kilometers away. At present, the local government has begun to relocate and provide economic compensation and housing assistance to the relocated residents. According to the report, Guizhou Reservoir Ecological Immigration Bureau provides subsidies according to the standard of 6.5438+0.2 million yuan per person; Guizhou Provincial Committee of Religious Affairs provides subsidies to ethnic minority families with housing difficulties according to the standard of 6.5438+0 million yuan per household.

Upon completion, the telescope will become the largest radio telescope in the world, far exceeding the 100m telescope in Bonn, Germany and the 300m telescope in Arecibo, USA, and will remain a world-class equipment in the next 20 to 30 years.