Geography questions

Refracting telescope

In 1608, Dutch eyeglass merchant Liebersee accidentally discovered that he could see distant scenery clearly with two lenses. Inspired by this, he made the first telescope in human history. A telescope.

In 1609, Galileo built a telescope with an aperture of 4.2 centimeters and a length of about 1.2 meters. He used a plano-convex lens as the objective lens and a concave lens as the eyepiece. This optical system was called a Galilean telescope. Galileo used this telescope to point at the sky and made a series of important discoveries, and astronomy entered the era of telescopes.

In 1611, the German astronomer Kepler used two biconvex lenses as the objective lens and eyepiece respectively, which significantly improved the magnification. From now on, this optical system was called the Keplerian telescope. . Nowadays, people still use these two types of refracting telescopes, and astronomical telescopes use the Keplerian type.

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

In 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, achromatic refractor telescopes have completely replaced long-bodied telescopes. However, due to technical limitations, it was difficult to cast larger flint glass. In the early days of achromatic telescopes, lenses of up to 10 cm could only be ground.

At the end of the 19th century, with the improvement of manufacturing technology, it became possible to manufacture larger-diameter refracting telescopes, and then there was a climax of manufacturing large-diameter refracting telescopes. Seven of the eight existing refractor telescopes over 70 cm in the world were built between 1885 and 1897. The most representative of them are the 102-cm-diameter Yekaishi Telescope built in 1897 and the 1886 The 91 cm LIKE telescope.

The advantages of refracting telescopes are long focal length, large film scale, and insensitivity to tube bending. They are most suitable for astronomical measurements. But it always has residual chromatic aberration, and at the same time it absorbs radiation in the ultraviolet and infrared bands very strongly. It was also very difficult to cast huge optical glass. By the completion of the Yekaishi Telescope in 1897, the development of refracting telescopes reached its peak. In the next hundred years, no larger refracting telescope appeared. This is mainly because it is technically impossible to cast a large piece of perfect glass to make a lens, and the deformation of a large-sized lens due to gravity will be very obvious, thus losing sharp focus.

Edit this paragraph Reflecting Telescope

The first reflecting telescope was born in 1668. After many attempts to grind aspherical lenses failed, Newton decided to use a spherical mirror as the primary mirror. He ground a 2.5 cm diameter metal into a concave reflector, and placed a reflector at an angle of 45° in front of the focus of the primary mirror, so that the condensed light reflected by the primary mirror passes through the reflector at an angle of 90°. The angular reflection exits the tube and reaches the eyepiece. This system is called a Newtonian reflecting telescope. Although its spherical mirror will produce certain aberrations, its use of reflective mirrors instead of refractors is a huge success.

James Gregory proposed a plan in 1663: using a primary mirror and a secondary mirror, both of which are concave mirrors. The secondary mirror is placed outside the focus of the primary mirror and in the main mirror. There is a small hole in the center, so that the light is reflected twice by the primary mirror and the secondary mirror and then emitted from the small hole to reach 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. This is theoretically correct, but the manufacturing level at the time could not meet this requirement. So Gregory couldn't get a mirror that would be useful to him.

In 1672, the Frenchman Cassegrain proposed a third design for a reflecting telescope. The structure was similar to that of the Gregorian telescope. The difference was that the secondary mirror was advanced before the focus of the primary mirror and was convex. Mirror, this is the most commonly used Cassegrain reflecting telescope. This makes the light reflected by the secondary mirror slightly divergent and reduces the magnification, but it eliminates spherical aberration, so that the focal length of the telescope can be very short.

The primary and secondary mirrors of Cassegrain telescopes can come in many different forms, with different optical properties. Because the Cassegrain telescope has a long focal length and a short lens body, the magnification is also large, and the resulting image is clear. It has both a Cassegrain focus, which can be used to study celestial objects in a small field of view, and a Newtonian focus, which can be used to photograph large areas. celestial body. Therefore, Cassegrain telescopes have been widely used.

Herschel was a master of making reflecting telescopes. He was a musician in his early years. Because of his hobby of astronomy, he began to polish telescopes in 1773. He made hundreds of telescopes in his lifetime. The telescope made by Herschel placed the objective lens obliquely in the lens tube, which caused parallel light to converge on one side of the lens tube after reflection.

In the nearly 200 years after the invention of the reflecting telescope, reflective materials have always been an obstacle to its development: the bronze used to cast the mirror is easy to corrode and has to be polished regularly, which requires a lot of money and time. A highly corrosive metal, denser than bronze and very expensive. In 1856, German chemist Justus von Liebig developed a method that could coat glass with a thin layer of silver. After being lightly polished, it could reflect light efficiently. This makes it possible to build better and larger reflecting telescopes.

At the end of 1918, the Hooke Telescope with an aperture of 254 cm was put into use, which was built under the leadership of Haier. Astronomers used this telescope to reveal for the first time the true size of the Milky Way and our location in it. More importantly, Hubble's theory of cosmic expansion was the result of observations using the Hooker telescope.

In the 1920s and 1930s, the success of the Hooker telescope inspired astronomers to build larger reflecting telescopes. In 1948, the United States built a 508-centimeter telescope. In commemoration of the outstanding telescope manufacturer Haier, it was named the Haier Telescope. It took more than 20 years from the design to the completion of the Hale Telescope. Although it can see farther and have stronger resolving power than the Hooker Telescope, it has not given mankind an updated understanding of the universe. As Asimov said: "The Hale Telescope (1948), like the Yerkes Telescope half a century ago (1897), seemed to herald the end of a particular type of telescope." . In 1976, the Soviet Union built a 600-centimeter telescope, but it was not as effective as the Hale telescope, which also confirms what Asimov said.

Reflecting telescopes have many advantages, such as: they have no chromatic aberration, they can record information from celestial bodies in a wide range of visible light, and they are easier to make than refracting telescopes. However, it also has inherent shortcomings: for example, the larger the aperture, the smaller the field of view, and the objective lens requires regular coating.

Edit this section Catadioptric Telescope

Catadioptric telescope first appeared in 1814. In 1931, the German optician Schmidt used a unique aspherical thin lens close to a parallel plate as a correction mirror, and cooperated with a spherical reflector to create a Schmidt-type folding lens that could eliminate spherical aberration and off-axis aberration. Reflecting telescope, this kind of telescope has strong light power, large field of view and small aberration. It is suitable for taking photos of large areas of the sky, especially the photo effects of faint nebulae are very outstanding. The Schmidt telescope has become an important tool for astronomical observation.

In 1940, Maksutov used a meniscus-shaped lens as a correction lens to create another type of catadioptric telescope. Its two surfaces are two spherical surfaces with different curvatures, which are not much different. , but the curvature and thickness are very large. All its surfaces are spherical, which is easier to grind than the correction plate of the Schmidt telescope. The lens barrel is also shorter, but the field of view is smaller than that of the Schmidt telescope, and the requirements for glass are also higher.

Because catadioptric telescopes can take into account the advantages of both refractive and reflective telescopes, they are very suitable for amateur astronomical observation and astronomical photography, and are loved by the majority of astronomical enthusiasts.

The light-gathering ability of the telescope increases as the aperture increases. The stronger the light-gathering ability of the telescope, the fainter and farther celestial objects can be seen. This actually means that the earlier universe can be seen. . Advances in astrophysics require larger aperture telescopes.

However, as the diameter of the telescope increases, a series of technical problems follow. The lens of the Haier telescope weighs 14.5 tons, the movable part weighs 530 tons, and the 6-meter mirror weighs 800 tons. The lens deformation caused by the dead weight of the telescope is considerable, and the uneven temperature causes distortion of the mirror surface and affects the image quality. From a manufacturing perspective, the cost of manufacturing telescopes using traditional methods is almost proportional to the square or cube of the diameter, so new methods must be found to manufacture telescopes with larger diameters.

Since the 1970s, many new technologies have been developed in the manufacturing of telescopes, involving fields such as optics, mechanics, computers, automatic control and precision machinery. These technologies enable the manufacturing of telescopes to break through the limitations of mirror aperture, reduce costs and simplify telescope structures. In particular, the emergence and application of active optical technology has made a leap forward in the design thinking of telescopes.

Since the 1980s, there has been an international craze for manufacturing a new generation of large telescopes. Among them, the main mirrors of the VLT of the European Southern Observatory, GEMINI, a cooperation between the United States, Britain and Canada, and SUBARU of Japan use thin mirrors; the main mirrors of the Keck I, Keck II and HET telescopes in the United States use splicing technology.

The excellent Cassegrain focus of traditional telescopes can concentrate 80% of the geometric light energy in the 0″.6 range under the best working conditions, while the new generation of large telescopes manufactured using new technologies It can keep 80% of the light energy concentrated at 0″.2~0″.4, or even better.

The following is an introduction to several representative large telescopes:

Keck telescope (Keck I, Keck II)

Keck I and Keck II was built in 1991 and 1996 respectively. It is the largest optical telescope that has been put into operation in the world. Its funding was mainly donated by entrepreneur Keck W M (Keck I was US$94 million, Keck II was US$94 million). for $74.6 million). These two identical telescopes are both placed on Mauna Kea, Hawaii, and are placed together for the purpose of conducting interference observations.

They are all 10 meters in diameter and are composed of 36 hexagonal mirrors. Each mirror has a diameter of 1.8 meters and a thickness of only 10 centimeters. The active optical support system keeps the mirrors extremely high. accuracy. There are three focal plane devices: near-infrared camera, high-resolution CCD detector and high-dispersion spectrometer.

"Large telescopes like Keck allow us to explore the origin of the universe along the long river of time. Keck allows us to see the first moment of the birth of the universe."

European Southern Observatory's Very Large Telescope (VLT)

The European Southern Observatory has been developing an optical telescope with an equivalent diameter of 16 meters, consisting of four 8-meter telescopes since 1986. These four 8-meter telescopes are arranged in a straight line. They are all RC optical systems with a focal ratio of F/2. They use a horizon device. The main mirror is supported by an active optical system. The pointing accuracy is 1″ and the tracking accuracy is 0.05″. The lens barrel weighs 100 tons and the fork arm weighs less than 120 tons. These four telescopes can form an interference array to perform pairwise interference observations, or each telescope can be used independently.

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

Gemini Telescope (GEMINI)

The Gemini Telescope is an international equipment mainly owned by the United States (of which the United States accounts for 50%, the United Kingdom accounts for 25%, Canada accounts for 15%, and Chile accounts for 15%. 5%, Argentina 2.5%, Brazil 2.5%), and is implemented by the American Universities Astronomy Alliance (AURA). It consists of two 8-meter telescopes, one in the northern hemisphere and one in the southern hemisphere, to conduct systematic observations of the whole sky. The primary mirror adopts active optical control, and the secondary mirror is a tilt mirror for rapid correction. It will also use an adaptive optical system to bring the infrared region close to the diffraction limit.

The project started in September 1993. The first unit was opened in Hawaii in July 1998, and the second unit was opened in September 2000 at the Serapajun site in Chile. The entire system is expected to It was officially put into use after acceptance in 2001.

Subaru (Japan) 8-meter telescope (SUBARU)

This is an 8-meter optical/infrared telescope. It has three characteristics: first, the mirror surface is thin and high imaging quality is obtained through active optics and adaptive optics; second, it can achieve high-precision tracking of 0.1″; third, it uses a cylindrical observation room with automatic control of ventilation and air filtration. device to achieve optimal conditions for eliminating thermal turbulence. This telescope uses a Serrurier truss to keep the primary mirror frame and secondary mirror frame parallel during movement.

The telescope will be installed on Mauna Kea, Hawaii, starting in 1991 and expected to be completed in nine years.

Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST)

This is a telescope under construction in my country with an effective clear aperture of 4 meters, a focal length of 20 meters and a field of view of 20-square-degree Neutral Reflection Schmidt telescope. Its technical features are:

1. Apply active optical technology to the reflective Schmidt system to correct spherical aberration in real time when tracking the movement of celestial bodies, achieving the function of both large aperture and large field of view.

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

3. The spectroscopic technology of multi-objective optical fibers (up to 4,000, compared with only 600 for ordinary telescopes) will be an important breakthrough.

LAMOST pushed the limit magnitude of galaxies for universal measurement to 20.5m, which is about 2 magnitudes higher than the SDSS plan. It achieved universal spectral measurement of 107 galaxies and increased the number of observation targets by one order of magnitude.

In 1932, Jansky K. G. used a radio antenna to detect radio radiation from the center of the Milky Way (in the direction of Sagittarius), which marked the beginning of human observation beyond the traditional optical band. The first window.

After the end of World War II, radio astronomy came to the fore. Radio telescopes played a key role in the development of radio astronomy, such as: the four major discoveries of astronomy in the 1960s, quasars, pulsars, interstellar Molecular and cosmic microwave background radiation are both observed using radio telescopes. Every great progress in radio telescopes will, without exception, set a milestone for the development of radio astronomy.

The University of Manchester in the United Kingdom built a fixed parabolic radio telescope with a diameter of 66.5 meters in 1946, and in 1955 it built the largest rotating parabolic radio telescope in the world at that time;

Six In the 1900s, the United States built a 305-meter-diameter parabolic radio telescope in the town of Arecibo, Puerto Rico. It was fixed on the ground along the hillside and could not rotate. It was the largest single-aperture radio telescope in the world.

In 1962, Ryle invented the synthetic aperture radio telescope, for which he won the 1974 Nobel Prize in Physics. The comprehensive aperture radio telescope achieves the same effect as a single large-aperture antenna by using multiple smaller antenna structures.

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

In the 1970s, the Federal Republic of Germany built a 100-meter-diameter omnidirectional rotating parabolic radio telescope near Bonn. This is the world's largest rotating single-antenna radio telescope.

Since the 1980s, the European VLBI Network (EVN), the American VLBA Array, and the Japanese Space VLBI (VSOP) have been put into use one after another. They are representatives of the new generation of radio telescopes. They have great advantages in sensitivity and resolution. The efficiency and observation band greatly exceed those of previous telescopes.

The two 25-meter radio telescopes of the Shanghai Observatory of the Chinese Academy of Sciences and the Urumqi Astronomical Station have participated in the Continuous Observation of Earth Rotation Program (CORE) in the United States and the Very Long Baseline Interferometry Network (EVN) in Europe as full members. The two programs are for Earth Rotation and High-precision Astrometric Research (CORE) and Astrophysical Research (EVN) respectively. This method of joint long-baseline interference observation by radio telescopes from various countries has achieved effects that no single country can achieve using large telescopes alone.

In addition, the 100-meter single-antenna telescope (GBT) developed by the National Astronomical Observatories (NARO) in the United States adopts unobstructed (offset feed), active optics and other designs. The antenna is currently being installed. In 2000 May be put into use.

The international community will jointly develop a low-frequency radio telescope array (SKA) with a receiving area of ??1 square kilometers. This plan will increase the sensitivity of low-frequency radio observations by approximately two orders of magnitude. Relevant countries are currently conducting various research projects. kind of preliminary research.

In terms of increasing the coverage of radio observation bands, the Smithsonian Astrophysical Observatory in the United States and the Taiwan Institute of Astronomy and Astrophysics are building the world's first submillimeter interference array (SMA) in Hawaii. It consists of eight 6-meter antennas, operating frequencies from 190GHz to 85z, and some equipment has been installed. The American Millimeter Wave Array (MMA) and the European Large Southern Array (LAS) will be merged into a new millimeter wave array program - ALMA. This plan will consist of 64 12-meter antennas, with the longest baseline reaching more than 10 kilometers, operating frequencies from 70 to 950 GHz, and will be placed near Atacama, Chile. If the merger goes smoothly, construction will begin in 2001. Japan is also considering participating. Possibilities of the program.

In terms of improving the angular resolution of radio observations, most of the new generation of large-scale equipment considers interference array solutions; in order to further improve the angular resolution and sensitivity of space VLBI observations, the second-generation space VLBI plan - ―ARISE (25-meter caliber) has been proposed.

It is believed that the completion and putting into use of these equipment will make radio astronomy an important research method in astronomy and bring unpredictable opportunities to the development of astronomy.

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

Optical window: This is the most important window, with wavelengths between 300 and 700 nanometers, including the visible light band (400 to 700 nanometers). Optical telescopes have always been the main tool for ground-based astronomical observations.

Infrared window: The infrared band ranges from 0.7 to 1000 microns. Since different molecules in the earth's atmosphere absorb infrared wavelengths inconsistently, the situation in the infrared band is more complicated. There are seven infrared windows commonly used for astronomical research.

Radio window: The radio band refers to electromagnetic waves with wavelengths greater than 1 millimeter. The atmosphere also absorbs a small amount of radio waves, but the atmosphere is almost completely transparent within the range of 40 mm to 30 meters. We generally call the range of 1 mm to 30 meters the radio window.

The atmosphere is opaque to other wavelength bands, such as ultraviolet, X-rays, γ-rays, etc. Astronomical observations of these bands were only realized after artificial satellites were launched into space.

Edit this section Infrared telescope

The earliest infrared observations can be traced back to the end of the 18th century. However, due to the absorption and scattering of the earth's atmosphere, infrared observations on the ground are limited to a few near-infrared windows. To obtain more information in the infrared band, space infrared observations must be carried out.

Modern infrared astronomical observations flourished in the 1860s and 1870s, when infrared telescopes or detectors carried by high-altitude balloons and aircraft were used for observation.

On January 23, 1983, the United States, Britain and the Netherlands jointly launched the first infrared astronomy satellite IRAS. Its main body is a telescope with an aperture of 57 cm, mainly engaged in sky survey work. 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 research target for astronomers.

On November 17, 1995, the Infrared Space Observatory (ISO), a collaboration between Europe, the United States and Japan, was launched into space and entered its intended orbit. The main body of ISO is an R-C telescope with an aperture of 60 cm. Its functions and performance are much improved than IRAS. It carries four observation instruments to realize imaging, polarization, spectroscopy, grating spectroscopy, and F-P interference. Spectrophotometry, metering and other functions. Compared with IRAS, ISO has a wider band range from near infrared to far infrared; has higher spatial resolution; higher sensitivity (about 100 times that of IRAS); and more functions.

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

From the Solar System to the Universe Large-scale infrared telescopes have many similarities or similarities with optical telescopes, so some modifications can be made to ground-based optical telescopes so that they can also perform infrared observations. In this way, these telescopes can be used to conduct infrared observations on moonlit nights or during the day, maximizing the efficiency of observation equipment.

Edit this section Ultraviolet telescope

The ultraviolet band is the frequency range between X-rays and visible light, and the observation band is 3100 to 100 Angstroms. Ultraviolet observations must be carried out at an altitude of 150 kilometers to avoid absorption by the ozone layer and the atmosphere. The first ultraviolet observation was carried out using a balloon to carry a telescope to a high altitude. Later, space technologies such as rockets, space shuttles and satellites were used to achieve real development in ultraviolet observation.

Observations in the ultraviolet band are of great astrophysical significance. The ultraviolet band is the frequency range between X-rays and visible light. Historically, the dividing line between ultraviolet and visible light was 3900 Angstroms. The standard for division at that time was whether it could be seen by the naked eye. The observation band of modern ultraviolet astronomy is 3100 to 100 Angstroms, which is adjacent to X-rays. This is because the ozone layer's absorption limit of electromagnetic waves is here.

In 1968, the United States launched OAO-2, and later Europe also launched TD-1A. Their mission was to conduct general survey observations of ultraviolet radiation in the sky. OAO-3, named Copernicus, was launched in 1972. It carried a 0.8-meter ultraviolet telescope and operated normally for 9 years, observing the ultraviolet spectrum of celestial objects from 950 to 3500 Angstroms.

The International Ultraviolet Explorer (IUE) was launched in 1978. Although the diameter of its telescope is smaller than that of Copernicus, its detection sensitivity has been greatly improved. IUE's observational data has become an important astrophysics research resource.

From December 2 to 11, 1990, the Space Shuttle Columbia carried the Astro-1 Observatory to conduct the first astronomical observation in the ultraviolet spectrum of the space laboratory; starting from March 2, 1995, the Astro-1 2 Observatory completed 16 days of ultraviolet astronomical observations.

In 1992, NASA launched an observation satellite, the Extreme Ultraviolet Exploration Satellite (EUVE), to conduct sky surveys in the extreme ultraviolet band.

The FUSE satellite was launched on June 24, 1999. It is one of NASA's "Origin Project" projects. Its mission is to answer basic questions about the evolution of the universe in astronomy.

Ultraviolet astronomy is an important part of full-band astronomy. In the 30 years since the launch of Copernicus, EUV (extreme ultraviolet), FUV (far ultraviolet), and UV have been developed in the ultraviolet band. (ultraviolet) and other detection satellites, covering all ultraviolet bands.

Called soft X-rays. X-rays from celestial bodies cannot reach the ground at all. Therefore, only after the artificial earth satellites were launched in the 1960s, astronomers obtained important observational results and X-ray astronomy developed. In the early days, the main focus was on observing X-rays from the sun.

In June 1962, a research team from the Massachusetts Institute of Technology in the United States discovered for the first time a powerful X-ray source coming from the direction of Scorpius, which brought non-solar X-ray astronomy into a rapid development stage. In the 1970s, the High Energy Observatory's No. 1 and No. 2 satellites were successfully launched, carrying out sky surveys in the X-ray band for the first time. This made X-ray observation research a big step forward and created a craze for X-ray observations.

Since the 1980s, various countries have successively launched satellites to conduct research on the X-ray band:

In April 1987, rockets from the former Soviet Union launched X-ray satellites developed by Germany, the United Kingdom, the former Soviet Union, the Netherlands and other countries. ray detectors were sent into space;

In 1987, Japan's X-ray detection satellite GINGA was launched into space;

In 1989, the former Soviet Union launched a high-energy astrophysics experimental satellite-GRANAT , it carries seven detection instruments developed by the former Soviet Union, France, Bulgaria, Denmark and other countries. Its main tasks are imaging, spectroscopy and observation and monitoring of explosive phenomena;

In June 1990, Roentgen The X-ray Astronomy Satellite (ROSAT for short) entered Earth orbit and obtained a large amount of important observation data for research work. So far, it has basically completed its scheduled observation mission;

The "Columbia" space shuttle in December 1990 The United States' "Broadband X-ray Telescope" was brought into space for nine days of observation;

In February 1993, Japan's "Tobi" X-ray detection satellite was launched into orbit by a rocket;

In 1996, the United States launched the "X-ray Photometry Explorer" (XTE).

On July 23, 1999, the United States successfully launched one of the Advanced X-ray Astrophysics Equipment (CHANDRA) Satellite, another one will be launched in 2000;

On December 13, 1999, the European Space Agency launched a satellite called XMM.

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

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

γ-ray telescope:

γ-rays have shorter wavelength and higher energy than hard Instruments carried by satellites.

In 1991, the Compton (γ-ray) Space Observatory (Compton GRO or CGRO) in the United States was launched into Earth orbit by the space shuttle. Its main mission is to conduct the first sky survey observation in the gamma wave band. It also conducts high-sensitivity and high-resolution imaging, energy spectrum measurement and light variation measurement of strong cosmic gamma-ray sources, and has achieved many results of great scientific value. .

CGRO is equipped with four instruments, which are orders of magnitude better in scale and performance than previous detection equipment. The successful development of these equipment has brought profound insights into the research of high-energy astrophysics. The change also marks the beginning of γ-ray astronomy gradually entering a mature stage. The four instruments carried by CGRO are: Burst and Temporary Source Experiment (BATSE), Variable Orientation Scintillation Spectrometer Experiment (OSSE), Imaging Telescope (COMPTEL) working in the range of 1Mev~30Mev, and Composition Telescope working in the range of 1Mev~30Mev. Elephant telescope (COMPTEL).

Inspired by the success of the Compton Space Observatory, scientific research institutions in Europe and the United States have cooperated to develop a new gamma-ray telescope project - INTEGRAL, which is ready to be sent into space in 2001. Its launch will provide a It laid the foundation for the further development of gamma-ray astronomy after the Putton Space Observatory.

We know that the earth’s atmosphere severely absorbs electromagnetic waves, and we can only conduct observations in radio, visible light and some infrared bands on the ground. With the development of space technology, it has become possible to observe outside the atmosphere, so there are space telescopes that can observe outside the atmosphere. Space observation equipment has great advantages over ground observation equipment: taking optical telescopes as an example, the telescope can receive a much wider waveband, and shortwave can even extend to 100 nanometers. Without atmospheric jitter, the resolving power can be greatly improved. There is no gravity in space, and the instrument will not be deformed due to its own weight. The observations of the ultraviolet telescope, X-ray telescope, gamma-ray telescope and some infrared telescopes introduced earlier are all carried out outside the earth's atmosphere and are also space telescopes.

Hubble Space Telescope (HST):

This is the first of four giant space observatories built under the auspices of NASA. It is also the largest and largest of all astronomical observation projects. The one with the most investment and the most public attention. It was planned to be built in 1978. The design lasted 7 years and was completed in 1989. It was launched by the space shuttle on April 25, 1990 at a cost of US$3 billion. However, due to spherical aberration of the primary mirror optical system caused by human factors, extensive repair work had to be carried out on December 2, 1993. The successful repair has enabled HST performance to meet or even exceed the original design goals. Observation results show that its resolution is dozens of times higher than that of large ground-based telescopes.

When HST initially launched, it carried five scientific instruments: the Wide Angle/Planetary Camera, the Faint Object Camera, the Faint Object Spectrograph, the High-Resolution Spectrograph and the High-Speed ??Photometer.

During the maintenance in 1997, second-generation instruments were installed for HST: a space telescope imaging spectrograph, a near-infrared camera and a multi-object spectrograph, which expanded the HST's observation range to the near-infrared and improved the efficiency in the ultraviolet spectrum.

During the maintenance in December 1999, the HST replaced the gyroscope and a new computer, and installed a third-generation instrument - an advanced census camera, which will improve the HST's ultraviolet-optical-near-infrared capabilities. Sensitivity and mapping performance.

HST has a very important impact on the development of the international astronomical community.

Space astronomical telescopes in the early 21st century:

The "Next Generation Large Space Telescope" (NGST) and the "Space Interferometry Mission" (SIM) are NASA's "origin programs" "'s key project to explore the first galaxies and star clusters that formed in the earliest days of the universe. Among them, NGST is a large-aperture passively cooled telescope with an aperture between 4 and 8 meters. It is a follow-up project to HST and SIRTF (Infrared Space Telescope). Its powerful observation capabilities are especially reflected in the large field of view and diffraction-limited imaging of optics, near-infrared and mid-infrared. The SIM that will operate in low-Earth orbit uses the Michael interference scheme to provide precise absolute positioning measurements of stars with milli-arc second accuracy. At the same time, it has comprehensive mapping capabilities and can produce high-resolution images, so it can be used to implement searches. other planets and other scientific purposes.

The "Astrophysics All-Celestial Astrometric 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 vast celestial body Physics research field. GAIA uses the Fizeau interference scheme with a field of view of 1°. The missions of GAIA and SIM are largely complementary.