How can an astronomical telescope see such a distant outer space?

Astronomical telescope is an important means to observe celestial bodies. It is no exaggeration to say that there would be no modern astronomy without the birth and development of telescopes. With the improvement of telescope performance in all aspects, astronomy is also experiencing a huge leap, which rapidly promotes human understanding of the universe.

From the first optical telescope to the birth of radio telescope for more than 300 years, optical telescope has been the most important tool for astronomical observation. Here is a brief introduction to the development of optical telescopes.

Refractive telescope

1608, a Dutch optician named Liporsay accidentally discovered that he could see the distant scenery with two lenses. Inspired by this, he built the first telescope in human history.

1609, Galileo made a telescope with a diameter of 4.2 cm and a length of about 1.2 m. He used a plano-convex lens as the objective lens and a concave lens as the eyepiece. This optical system is called galileo telescope. Galileo aimed his telescope at the sky and made a series of important discoveries. Astronomy has entered the era of telescopes.

16 1 1 year, German astronomer Kepler used two biconvex lenses as the objective lens and eyepiece respectively, which significantly improved the magnification. Later, people called this optical system Kepler telescope. Now people are still using these two kinds of refractive telescopes, and the astronomical telescope adopts Kepler type.

It should be pointed out that at that time, because the telescope used a single lens as the objective lens, there was serious chromatic aberration. In order to obtain good observation effect, a lens with small curvature is needed, which will inevitably lead to the lengthening of the mirror body. So for a long time, astronomers have been dreaming of making longer telescopes, and many attempts have ended in failure.

1757, Dulong established the theoretical basis of achromatic lenses by studying the refraction and dispersion of glass and water, and made achromatic lenses with crown glass and flint glass. Since then, the achromatic refraction telescope has completely replaced the long mirror telescope. However, due to technical limitations, it is difficult to cast large flint glass. At the beginning of achromatic telescope, only 10 cm lens can be ground at most.

At the end of 19 century, with the improvement of manufacturing technology, it became possible to manufacture large-aperture refractive telescopes, and the climax of manufacturing large-aperture refractive telescopes appeared. Of the eight existing refracting telescopes over 70 cm in the world, seven were built between 1885 and 1897, among which the most representative ones are the Yekeshi telescope with the aperture of 102 cm built in 1897 and the 9/kloc telescope built in 1886.

Refractive telescope has the advantages of long focal length, large negative scale and insensitivity to lens barrel bending, and is most suitable for astrometry. But there will always be residual color difference, and at the same time, it absorbs radiation in ultraviolet and infrared bands very strongly. The casting of huge optical glass is also very difficult. When the Yekeshi telescope was built in 1897, the development of refractive telescope reached its peak, and no larger refractive telescope appeared in the next hundred years. This is mainly because it is technically impossible to cast a large piece of perfect glass as a lens, and the large-size lens will be deformed obviously due to the action of gravity, thus losing Ming Rui's focus.

Reflecting telescope:

The first reflecting telescope was born in 1668. Newton decided to use a spherical mirror as the main mirror after many failures in grinding aspheric lenses. He grinds out a concave mirror with a diameter of 2.5cm, and places a reflector with an angle of 45o in front of the focus of the main mirror, so that the concentrated light reflected by the main mirror can be reflected from the lens barrel to the eyepiece at an angle of 90o. This system is called Newton reflecting telescope. Although its spherical mirror will produce some aberrations, it is very successful to replace the refracting mirror with the reflecting mirror.

In 1663, James Gregory proposed a scheme: use a primary mirror and a secondary mirror, both of which are concave mirror. The secondary mirror is placed outside the focus of the primary mirror, and a small hole is left in the center of the primary mirror, so that the light is reflected twice by the primary mirror and the secondary mirror and then exits from the small hole and reaches the eyepiece. The purpose of this design is to eliminate spherical aberration and chromatic aberration at the same time, which requires a parabolic primary mirror and an ellipsoidal secondary mirror, which is correct in theory, but the manufacturing level at that time could not meet this requirement, so Gregory could not get a useful mirror for him.

1672, Frenchman seglin put forward the third design scheme of reflective telescope. The structure is similar to Gregory telescope, except that the secondary mirror is convex in front of the focus of the primary mirror, which is the most commonly used Cassegrain reflective telescope. This makes the light reflected by the secondary mirror slightly divergent, reducing the magnification, but eliminating the spherical aberration, so that the telescope can also make the focal length very short.

The primary mirror and secondary mirror of seglin telescope can have many different forms, and their optical properties are also different. Because of the long focal length, short mirror body and large magnification of seglin telescope, the images obtained are clear; Seglin focus can be used to study celestial bodies with small field of view, while Newton focus can be configured to shoot large-area celestial bodies. Therefore, seglin telescope has been widely used.

Herschel is a master of making reflecting telescope. He was a musician in his early years. Because he loves astronomy, he began to grind telescopes from 1773 and made hundreds of telescopes in his life. In the telescope made by Herschel, the objective lens is obliquely placed in the lens barrel, so that the parallel light is reflected and converged on one side of the lens barrel.

In the nearly 200 years after the invention of reflective telescope, reflective materials have been an obstacle to its development: bronze casting mirrors is easy to corrode and must be polished regularly, which requires a lot of money and time, while metals with good corrosion resistance are denser and more expensive than bronze. 1856, justus von liebig, a German chemist, invented a method that can coat a thin layer of silver on glass and reflect light efficiently after polishing. In this way, it is possible to make a better and larger reflective telescope.

19 18 At the end of this year, the Hooke telescope with a diameter of 254 cm was put into use and was built by Haier. Astronomers used this telescope to reveal for the first time the true size of the Milky Way and our position in it. More importantly, Hubble's theory of cosmic expansion is the result of observation with Hooke telescope.

In the 1920s and 1930s, the success of Hooke Telescope inspired astronomers to build a bigger reflecting telescope. 1948, the United States built a telescope with a diameter of 508 cm. In order to commemorate Haier, an outstanding telescope manufacturer, it was named Haier Telescope. Haier telescope has been designed and manufactured for more than 20 years. Although it has a farther field of vision and stronger resolution than Hooke telescope, it has not given mankind an updated understanding of the universe. As Asimov said, "The Haier telescope (1948), like the Yekeshi telescope (1897) half a century ago, seems to indicate that a certain type of telescope has almost come to an end". 1976, the former Soviet Union built a 600 cm telescope, but its function is not as good as Haier telescope, which also confirms what Asimov said.

Reflective telescope has many advantages, for example, it has no chromatic aberration, can record the information sent by celestial bodies in a wide range of visible light, and is easier to make than refractive telescope. However, due to its inherent shortcomings, such as the larger the aperture, the smaller the field of view, and the need for periodic coating of the objective lens.

Reflective refraction telescope;

Reflecting telescope first appeared in 18 14. 193 1 year, the German optician Schmidt used a unique aspheric thin lens close to a parallel plate as a correcting mirror, and cooperated with a spherical reflector to make a Schmidt-type folded reflecting telescope that can eliminate spherical aberration and off-axis aberration. This kind of telescope has strong optical power, large field of view and small aberration, and is suitable for shooting large-area photos of the sky, especially for shooting dim nebulae. Schmidt telescope has become an important tool for astronomical observation.

1940, Maksutov made another kind of folded reflecting telescope with meniscus lens as corrective lens. Its two surfaces are two spherical surfaces with different curvatures, with little difference, but with great curvature and thickness. All its surfaces are spherical, which makes it easier to grind than the correction plate of Schmidt telescope, and the lens barrel is shorter, but the field of view is smaller than that of Schmidt telescope, which requires higher glass.

Because folding reflecting telescope can take into account the advantages of both refractive and reflective telescopes, it is very suitable for amateur astronomical observation and astrophotography, and is loved by the vast number of astronomical enthusiasts.

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 6-meter mirror is 800 tons. The lens deformation caused by the self-weight of the telescope is quite large, and the uneven temperature distorts the mirror surface, which affects 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, Subaru of Japan, etc. use thin mirrors as primary mirrors; The primary mirrors of Keck I, Keck II and HET telescopes in the United States all adopt splicing technology.

In the best working condition, the excellent Segreen Jiao of the traditional telescope can concentrate 80% of the geometric light energy in the range of 0.6, 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 some representative large telescopes:

Keck telescope (Keck 1, Keck 2)

Keck I and Keck II were built in 199 1 and 1996 respectively. They are the largest optical telescopes that have been put into operation in the world at present, and they are named because their funds are mainly donated by entrepreneur Keck W M (Keck I is 94 million US dollars and Keck II is 74.6 million US dollars). 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.

European Southern Observatory Very Large Telescope (VLT)

Since 1986, the European Southern Observatory has been developing an optical telescope with an equivalent aperture of16m, which consists of four 8m telescopes. Four 8-meter telescopes are arranged in a straight line. Both are RC optical systems, and the focal length ratio is F/2. The primary mirror is supported by an active optical system. Pointing accuracy1",tracking accuracy 0.05", lens barrel weight100t, and fork arm weight less than10t. These four telescopes can form an interference array, do interference observation in pairs, or they can be used independently.

Two of them have been completed and are expected to be completed in 2000.

Gemini telescope (Gemini)

Gemini telescope is an international equipment led by the United States (including 50% in the United States, 25% in Britain, 0/5% in Canada/KLOC, 5% in Chile, 2.5% in Argentina and 2.5% in Brazil), and it is implemented by the Astronomical Union of American Universities (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, the secondary mirror is quickly corrected by tilting mirror, and the infrared region will approach the diffraction limit through adaptive optical system.

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.

Pleiades (Japan) 8 m telescope (Subaru)

This is an 8-meter optical/infrared telescope. 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.

This telescope will be installed in Monaque Asia, starting from 199 1 and expected to be completed in 9 years.

Large area multi-target optical fiber spectral telescope (LAMOST)

This is a reflective Schmidt telescope under construction in China, with an effective aperture of 4 meters, a focal length of 20 meters 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 Bonn, 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.

We know that there is a thick atmosphere on the surface of the earth. Due to the interaction (mainly absorption and reflection) between various particles in the earth's atmosphere and celestial radiation, celestial radiation in most bands cannot reach the ground. People vividly call the band that can reach the ground "atmospheric window", and there are three such "windows".

Optical window: This is the most important window, with the wavelength between 300-700 nm, including the visible light band (400-700 nm). Optical telescope has always been the main tool for astronomical observation on the ground.

Infrared window: the range of infrared band is between 0.7 ~ 1000 micron, and the situation of infrared band is more complicated because of the different infrared wavelengths absorbed by different molecules in the earth's atmosphere. Astronomical research usually uses seven infrared windows.

Radio window: Radio band refers to electromagnetic wave with wavelength greater than1mm.. The atmosphere also absorbs a small number of radio bands, but the atmosphere is almost completely transparent in the range of 40 mm to 30 m. We generally call the range of 1 mm to 30 m the radio window.

The atmosphere is opaque to other bands, such as ultraviolet, X-ray and γ-ray. Astronomical observation of these bands can only be realized after a few days on the satellite.

Infrared telescope:

The earliest infrared observation can be traced back to the end of the eighteenth century. However, due to the absorption and scattering of the earth's atmosphere, the infrared observation on the ground is limited to a few near-infrared windows. In order to obtain more infrared band information, space infrared observation is necessary. Modern infrared astronomical observation flourished in the 1960s and 1970s, when high-altitude balloons and infrared telescopes or detectors carried by airplanes were used for observation.

1983 65438+1On October 23rd, the first infrared astronomical satellite IRAS was jointly launched by the United States, Britain and the Netherlands. Its main body is a telescope with a diameter of 57 cm, which is mainly engaged in surveying the sky. The success of IRAS has greatly promoted the development of infrared astronomy at all levels. Until now, the observation source of IRAS is still a hot target for astronomers to study.

1995165438+1October 17 was launched by the infrared space observatory (ISO) in cooperation with Europe, America and Japan and entered the scheduled orbit. The main body of ISO is an R-C telescope with a diameter of 60 cm. Its function and performance are much better than IRAS. It carries four observation instruments to realize imaging, polarization, light splitting, grating light splitting, F-P interference light splitting, photometry and other functions. Compared with IRAS, ISO has a wider band range, from near infrared to far infrared. Has higher spatial resolution; The sensitivity is higher (about 100 times that of IRAS); And more functions.

The actual working life of ISO is 30 months, and the fixed-point observation of the target (IRAS observation is sky survey observation) can solve the problems raised by astronomers in a targeted manner. It is predicted that the research based on ISO data will become one of the hot spots in astronomy in the next few years.

Large infrared telescopes from the solar system to the universe have many similarities or similarities with optical telescopes, so some modifications can be made to the optical telescopes on the ground so that they can also engage in infrared observation. In this way, these telescopes can carry out infrared observation in the moonlit night or during the day, and give full play to the efficiency of observation equipment.

Ultraviolet telescope:

Ultraviolet band is the frequency range between X-ray and visible light, and the observation band is 3 100 ~ 100 angstrom. Ultraviolet observation should be carried out at the height of 150 km to avoid the absorption of ozone layer and atmosphere. The first ultraviolet observation was to carry a telescope into the sky with a balloon. Later, the use of rockets, space shuttles, satellites and other space technologies made the real development of ultraviolet observation.

The observation of ultraviolet band is of great significance in astrophysics. Ultraviolet band is a frequency range between X-ray and visible light. Historically, the dividing line between ultraviolet and visible light was 3900 angstroms. At that time, the dividing standard was whether it could be seen by naked eyes. The observation band of modern ultraviolet astronomy is 3 100 ~ 100 angstrom, which is connected with x-rays, because the absorption limit of the ozone layer to electromagnetic waves is here.

1968 OAO-2 was introduced in the United States, and TD- 1A was introduced in Europe. Their task is to make a comprehensive investigation of ultraviolet radiation in the sky. OAO-3 was named Copernicus and launched in 1972. It carried a 0.8-meter ultraviolet telescope and operated normally for 9 years, observing the ultraviolet spectrum of celestial bodies from 950 angstroms to 3500 angstroms.

The International Ultraviolet Detector (IUE) was launched in 1978. Although the aperture of its telescope is smaller than Copernicus's, its detection sensitivity is greatly improved. The observation data of IUE has become an important astrophysical research resource.

1990 65438+February 2 ~ 1 1 day, the space shuttle Columbia carried Astro- 1 observatory and made the first astronomical observation of ultraviolet spectrum in the space laboratory. From/kloc-0 to March 2, 995, Astro-2 Observatory completed the ultraviolet astronomical observation for 16 days.

From 6: 438 to 9: 92, NASA launched an observation satellite EUVE to observe the sky in the extreme ultraviolet band.

FUSE satellite was launched on June 24th, 1999/KLOC-0, which is one of the "Origin Plan" projects of NASA. Its task is to answer the basic questions about the evolution of the universe in astronomy.

Ultraviolet astronomy is an important part of all-band astronomy. Since Copernicus launched 30 years ago, various exploration satellites such as EUV (extreme ultraviolet), FUV (extreme ultraviolet) and UV (ultraviolet) have been developed in the ultraviolet band, covering all ultraviolet bands.

X-ray telescope:

The wavelength range of X-ray radiation is 0.0 1- 10 nm, where the shorter wavelength (higher energy) is called hard X-ray and the longer wavelength is called soft X-ray. X-rays emitted by celestial bodies cannot reach the ground at all, so it was not until the launch of artificial earth satellites in the 1960s that astronomers made important observations and X-ray astronomy was developed. In the early days, it was mainly to observe the x-rays of the sun.

1in June, 962, the research team of Massachusetts Institute of Technology first discovered a powerful X-ray source from Scorpio, which made non-solar X-ray astronomy enter a stage of rapid development. In the 1970s, two satellites, the High Energy Observatory 1 and 2, were successfully launched, and the X-ray band survey was conducted for the first time, which made the X-ray observation research take a big step forward and formed an X-ray observation upsurge. Since 1980s, many countries have launched satellites to study the X-ray band:

1987 In April, the X-ray detector developed by Germany, Britain, the former Soviet Union and the Netherlands was sent into space by a rocket of the former Soviet Union.

1987 Japan's X-ray exploration satellite GINGA was launched;

1989 The former Soviet Union launched a high-energy astrophysics experimental satellite-Granat, which carried seven detection instruments developed by the former Soviet Union, France, Bulgaria and Denmark. Its main work is imaging, spectroscopy and observing and monitoring the explosion phenomenon.

1June, 990, Roentgen X-ray Astronomical Satellite (ROSAT for short) entered Earth orbit and obtained a large number of important observation data for research work. Up to now, the scheduled observation task has been basically completed.

19901In February 1990, the space shuttle Columbia took the American broadband X-ray telescope into space for nine days.

1in February 1993, the Japanese "Bird" X-ray exploration satellite was put into orbit by a rocket;

1996, the United States launched the X-ray photometric detection satellite (XTE).

1On July 23rd, 1999, the United States successfully launched a satellite with the advanced X-ray astrophysical equipment (CHANDRA), and another satellite will be launched in 2000.

The European Community Space Agency launched a satellite named XMM.

In 2000, Japan will also launch an X-ray observation device.

The above projects and plans show that the next few years will be the climax of X-ray observation and research.

Gamma-ray telescope;

Gamma rays have shorter wavelength and higher energy than hard X rays. Because of the absorption of the earth's atmosphere, the astronomical observation of gamma rays can only be carried out by instruments carried by high-altitude balloons and artificial satellites.

199 1 year, the Compton (γ-ray) Space Observatory (Compton GRO or CGRO) was put into Earth orbit by the space shuttle. Its main task is to carry out the first survey of the γ -band sky, and at the same time, it has carried out high-sensitivity and high-resolution imaging, energy spectrum measurement and light variation measurement of the strong cosmic γ -ray source, and achieved many achievements with great scientific value.

CGRO is equipped with four instruments. Compared with the previous detection equipment, the scale and performance of these instruments have been improved by an order of magnitude. The successful development of these instruments has brought profound changes to the research of high-energy astrophysics, and also marked that γ -ray astronomy has gradually entered a mature stage. The four instruments CGRO carries are: Burst and Transient Source Experiment (BATSE), Variable Direction Scintillation Spectrometer Experiment (OSSE), Imaging Telescope (COMPTEL) operating in the range of 1Mev~30Mev and Imaging Telescope (COMPTEL) operating in the range of 1Mev~30Mev.

Encouraged by the success of Compton Space Observatory, European and American scientific research institutions have formulated a new gamma-ray telescope project-Integral, which will be launched into space on 200 1, and its launch will lay the foundation for the further development of gamma-ray astronomy after Compton Space Observatory.

We know that the earth's atmosphere absorbs electromagnetic waves seriously, and only radio, visible light and some infrared bands can be observed on the ground. With the development of space technology, it is possible to observe outside the atmosphere, so there are space telescopes that can observe outside the atmosphere. Compared with ground observation equipment, space observation equipment has great advantages: taking optical telescope as an example, the wavelength band that the telescope can receive is much wider, and the short wave can even be extended to 100 nanometer. Without atmospheric jitter, the resolution can be greatly improved, and there is no gravity in space, so the instrument will not be deformed by its own weight. The observation of ultraviolet telescope, X-ray telescope, gamma-ray telescope and some infrared telescopes mentioned above are all carried out outside the earth's atmosphere and belong to space telescopes.

Hubble Space Telescope;

This is the first of the four giant space observatories built under the auspices of NASA, and it is also the largest, most expensive and most popular astronomical observation project. It was built in 1978, designed for 7 years, completed in 1989, and launched by the space shuttle on April 25, 1990, costing US$ 3 billion. However, due to the spherical aberration of the primary mirror optical system caused by human factors, a large-scale repair work had to be carried out on199365438+February 2. The success of the repair makes the performance of HST reach or even exceed the original design goal. The observation results show that its resolution is dozens of times higher than that of large ground telescopes.

When HST was launched, it was equipped with five scientific instruments: wide-angle/planetary camera, dim celestial camera, dim celestial spectrometer, high-resolution spectrometer and high-speed photometer.

During the maintenance of 1997, the second generation instruments were installed for HST, including space telescope imaging spectrometer, near infrared camera and multi-target spectrograph, which extended the observation range of HST to near infrared and improved the efficiency of ultraviolet spectrum.

Maintenance of1Feb. 9 1999 replaced the gyroscope and new computer for HST, and installed the third generation instrument-advanced census camera, which will improve the sensitivity and mapping performance of HST in ultraviolet-optical-near infrared.

HST has a very important influence on the development of international astronomy.

2/kloc-0 space astronomical telescope at the beginning of the century;

The Next Generation Large Space Telescope (NGST) and Space Interferometry Mission (SIM) are the key projects of NASA's Origin program, which are used to explore the first galaxies and clusters formed in the earliest universe. Among them, NGST is a large-caliber passive refrigeration telescope with a diameter of 4 ~ 8 meters, which is a follow-up project of HST and SIRTF (Infrared Space Telescope). Its powerful observation ability is especially reflected in optics, near-infrared and mid-infrared wide field of view, diffraction limit mapping and so on. SIM running in low-earth orbit adopts Michael interference scheme to provide accurate absolute positioning measurement of stars with the accuracy of milli-angular seconds. At the same time, because of its ability to synthesize maps and generate high-resolution images, it can be used for scientific purposes such as searching for other planets.

"Astrophysics All-Sky Astrometry Interferometer" (GAIA) will conduct a comprehensive and thorough survey of the overall geometric structure and kinematics of the Milky Way, and on this basis, open up a broad field of astrophysics research. Gaia adopts Fizeau interference scheme, and the field of view is 1. The tasks of Gaia and SIM are largely complementary.