The principle of a telescope is to use two convex lenses to continuously magnify the image presented.
A telescope/binoculars
Basic principles of a telescope
A telescope is a visual optical instrument used to observe distant objects. The small opening angle of distant objects is enlarged by a certain magnification, so that it has a larger opening angle in the image space, making objects that cannot be seen or distinguished clearly with the naked eye become clear and distinguishable. Therefore, the telescope is an indispensable tool in astronomy and ground observation. It is an optical system that allows the incident parallel light beams to remain parallel and emitted through the objective lens and eyepiece. According to the principle of telescopes, they are generally divided into three types.
An instrument that collects electromagnetic waves to observe distant objects. In daily life, telescopes mainly refer to optical telescopes. But in modern astronomy, astronomical telescopes include radio telescopes, infrared telescopes, X-ray and gamma-ray telescopes. In recent years, the concept of astronomical telescopes has been further extended to the fields of gravitational waves, cosmic rays and dark matter.
In daily life, an optical telescope is usually a cylindrical optical instrument. It focuses light to form a direct image through the refraction of a lens or the reflection of a concave mirror, or it passes through a magnifying eyepiece. Make observations. Optical telescopes in daily life are also called "telescopes". It mainly includes amateur astronomical telescopes, theater telescopes and military binoculars. [Edit this paragraph] Introduction
Commonly used binoculars also need to add a prism system for the purpose of reducing the size and flipping the inverted image. The prism system can be divided into a Biehan prism system and a Porro prism according to different forms. systems, the principles and applications of the two systems are similar.
Small handheld telescopes for personal use should not be used with excessive magnification, generally 3 to 12 times. When the magnification is too large, the image clarity will become worse and the jitter will be serious, exceeding 12 times. Telescopes are generally fixed using tripods and other methods. [Edit this paragraph] History
One day in the early 17th century, Hans Lippershey, the owner of an optical shop in a small Dutch town, put a convex lens and a concave lens together to check the quality of the ground lenses. The mirrors were aligned in a line, and when I looked through the lens, I found that the church spire in the distance seemed to be getting bigger and closer, so I accidentally discovered the secret of the telescope. In 1608, he applied for a patent for the telescope he made and complied with the authorities' request to build a pair of binoculars. It is said that dozens of opticians in the town claim to have invented the telescope, but Liebersch is generally supported as the inventor of the telescope.
News of the invention of the telescope quickly spread throughout Europe. After learning about the news, Italian scientist Galileo Galilei made his own one. The first telescopes could only magnify objects 3 times. A month later, the second telescope he built could magnify 8 times, and the third telescope could magnify 20 times. In October 1609, he built a telescope that could magnify 30 times. Galileo used a homemade telescope to observe the night sky and discovered for the first time that the moon's surface was rugged, covered with mountains and had cracks in craters. After that, he discovered the four satellites of Jupiter and the sunspot movement of the sun, and concluded that the sun is rotating.
At the same time, the German astronomer Kepler also began to study telescopes. He proposed another astronomical telescope in "Diopters". This telescope was composed of two convex lenses and was similar to Galileo's telescope. Different, it has a wider field of view than the Galilean telescope. But Kepler did not build the telescope he described. Scheiner first made this kind of telescope between 1613 and 1617. He also followed Kepler's suggestion and made a telescope with a third convex lens, turning the inverted image of the telescope made of two convex lenses into an upright image. . Scheiner built 8 telescopes and observed the sun one by one. No matter which one, he could see the same shape of sunspots. Therefore, he dispelled many people's illusion that sunspots may be caused by dust on the lens, and proved that sunspots are indeed observed.
Scheiner installed special light-shielding glass when observing the sun, but Galileo did not add this protective device. As a result, he injured his eyes and was almost blind in the end. In order to reduce the chromatic aberration of the refractor telescope, Huygens of the Netherlands built a telescope with a tube length of nearly 6 meters in 1665 to explore the rings of Saturn. Later, he also built a telescope with a length of nearly 41 meters.
A telescope that uses a lens as a crop mirror is called a refracting telescope. Even if the lens tube is lengthened and the lens is precisely processed, the chromatic aberration cannot be eliminated. Newton once thought that the chromatic aberration of the refracting telescope was irremediable, but it was later proven that it was Too pessimistic. In 1668, he invented the reflecting telescope, which solved the problem of chromatic aberration. The first reflecting telescope was very small. The diameter of the mirror in the telescope was only 2.5 centimeters, but it could already clearly see the moons of Jupiter and the phases of Venus. In 1672, Newton built a larger reflecting telescope and gave it to the Royal Society. It is still kept in the library of the Royal Society. In 1733, the Englishman Hal made the first achromatic refractor telescope. In 1758, Paul Land of London also made the same telescope. He used glasses with different refractive indexes to make convex lenses and concave lenses respectively, and the colored edges formed by them canceled each other out. But it is not easy to make a very large lens. Currently, the largest refracting telescope in the world has a diameter of 102 centimeters and is installed at the Ardis Observatory. In 1793, William Herschel of England made a reflecting telescope. The diameter of the reflecting mirror was 130 centimeters, made of copper-tin alloy, and weighed 1 ton. The reflecting telescope made by William Parsons in England in 1845 had a reflector diameter of 1.82 meters. In 1917, the Hooker Telescope was built at Mount Wilson Observatory in California, USA. Its primary reflector has a diameter of 100 inches. It was using this telescope that Edwin Hubble discovered the astonishing fact that the universe is expanding. In 1930, German Bernhard Schmidt combined the advantages of refracting telescopes and reflecting telescopes (refracting telescopes have small aberrations but have chromatic aberration and are more expensive the larger they are, while reflecting telescopes have no chromatic aberration, are low-cost and can be made very large. But there are aberrations) combined to create the first catadioptric telescope.
After the war, reflecting telescopes developed rapidly in astronomical observations. In 1950, a 5.08-meter-diameter Hale reflecting telescope was installed on Palomar Mountain. In 1969, a 6-meter-diameter reflector was installed on Mount Pastukhov in the northern Caucasus of the former Soviet Union. In 1990, NASA launched the Hubble Space Telescope into orbit. However, due to a mirror failure, the Hubble Telescope did not begin to fully function until astronauts completed space repairs and replaced the lens in 1993. Because it is not interfered by the Earth's atmosphere, Hubble's images are 10 times clearer than those captured by similar telescopes on Earth. In 1993, the United States built the 10-meter Keck Telescope on Mauna Kea, Hawaii. Its mirror is made up of 36 1.8-meter reflectors. In 2001, the European Southern Observatory in Chile completed the development of the "Very Large Telescope" (VLT), which consists of four telescopes with an aperture of 8 meters and has a light-gathering capacity equivalent to that of a 16-meter reflecting telescope. Now, a group of telescopes under construction have begun to attack the white giant brothers on Mauna Kea. These new contenders include the 30-meter California Extremely Large Telescope (CELT), the 20-meter Giant Magellan Telescope (GMT) and the 100-meter Extremely Large Telescope (CELT). Overwhelming Large Telescope (OWL for short).
Their advocates point out that these new telescopes will not only provide images of space that are far better than Hubble's images, but also collect more light to study the initial state of stars and cosmic gas when galaxies formed 10 billion years ago. Learn more about the situation and see clearly the planets around distant stars.
Classification
1. Refracting telescope is a telescope that uses a lens as a crop mirror. It is divided into two types: a Galilean telescope with a concave lens as the eyepiece; a Keplerian telescope with a convex lens as the eyepiece. Because the chromatic aberration and spherical aberration of single-lens objective lenses are quite serious, modern refractor telescopes often use two or more lens groups as objective lenses. Among them, the double lens objective lens is the most commonly used. It consists of a convex lens made of a crown glass and a concave lens made of flint glass that are very close to each other. It completely eliminates positional chromatic aberration for two specific wavelengths, and can also weaken the positional chromatic aberration of other wavelengths accordingly
When certain design conditions are met, spherical aberration and coma can also be eliminated. Due to the influence of residual chromatic aberration and other aberrations, the relative aperture of a double-lens objective lens is small, generally 1/15-1/20, rarely larger than 1/7, and the available field of view is not large. A double-lens objective with an aperture less than 8 cm can have two lenses glued together and is called a double-cemented objective. A certain gap left unglued is called a double-separate objective. In order to increase the relative aperture and field of view, a multi-lens objective lens group can be used. For Galileo's telescope, the structure is very simple and the loss of light energy is small. The lens barrel is short and very light. It also forms an erect image, but has a small magnification and a narrow field of view. It is generally used in theater mirrors and toy telescopes. For the Kepler telescope, a prism group or a lens group needs to be added behind the objective lens to convert the image so that the eyes observe an erect image. General refracting telescopes adopt Keplerian structure. Since the imaging quality of refracting telescopes is better than that of reflecting telescopes, the field of view is large, it is easy to use, and it is easy to maintain. Small and medium-sized astronomical telescopes and many special instruments mostly use refractive systems. However, large refracting telescopes are much more difficult to manufacture than reflecting telescopes because of the large smelting requirements. It is very difficult to obtain a high-quality lens with a large aperture, and there is a problem with the absorption of light by glass, so large-aperture telescopes all use reflection type
(detailed introduction below)
Galileo Telescope
A telescope in which the objective lens is a converging lens and the eyepiece is a diverging lens. The real image formed by the refraction of light through the objective lens is at the focus behind the eyepiece (near the back of the human eye). This image is a virtual image to the eyepiece, so it becomes an enlarged upright virtual image after being refracted by it. The magnification of a Galilean telescope is equal to the ratio of the focal length of the objective lens to the focal length of the eyepiece. The advantage is that the lens barrel is short and can form an erect image, but its field of view is relatively small. A device that puts two Galilean telescopes with low magnification side by side and uses a bolt button in the middle to adjust their clarity at the same time is called a "theater scope"; because it is easy to carry, it is often used to watch performances, etc. The telescope invented by Galileo played an important role in the history of human understanding of nature. It consists of a concave lens (eyepiece) and a convex lens (objective lens). Its advantage is that it has a simple structure and can directly form a positive image.
The Kepler telescope
The principle consists of two convex lenses. Since there is a real image between the two, the reticle can be easily installed and the performance is excellent. Therefore, professional-level telescopes such as military telescopes and small astronomical telescopes currently use this structure. However, the imaging of this structure is inverted, so an upright imaging system needs to be added in the middle.
There are two types of erect image systems: prism erect image systems and lens erect image systems. Our common typical binoculars with a wide front and narrow back adopt a double right-angle prism erect image system. The advantage of this system is that the optical axis is folded twice while erecting the image, thereby greatly reducing the size and weight of the telescope. The lens erecting system uses a complex set of lenses to invert the image, which is relatively expensive, but the Russian 20×50 three-section telescopic classical monocular telescope uses a well-designed lens erecting system.
History
In 1608, the Dutch eyeglass merchant Liebersay accidentally discovered that he could see distant scenery clearly with two lenses. Inspired by this, he built the first airplane in human history. telescope.
In 1609, Galileo 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. Astronomy has since 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 due to gravity, the deformation of a large-sized lens will be very obvious, thus losing sharp focus.
2. Reflecting telescope is a telescope that uses a concave reflector as a crop mirror. It can be divided into several types such as Newtonian telescope and Cassegrain telescope. The main advantage of a reflecting telescope is that there is no chromatic aberration. When the objective lens adopts a paraboloid, it can also eliminate spherical aberration. However, in order to reduce the influence of other aberrations, the available field of view is smaller. The materials used to make the reflector only require a small expansion coefficient, low stress and ease of grinding. Polished reflectors are generally coated with an aluminum film on the surface. The reflectivity of the aluminum film in the 2000-9000 Angstrom band range is greater than 80. Therefore, in addition to the optical band, the reflecting telescope is also suitable for research in the near-infrared and near-ultraviolet bands. . The relative aperture of a reflecting telescope can be made larger. The relative aperture of a main focus reflecting telescope is about 1/5-1/2.5 or even larger. Besides, except for Newtonian telescopes, the length of the lens tube is much shorter than the focal length of the system. In addition, only one surface of the main mirror needs to be processed, which greatly reduces the cost and manufacturing difficulty. Therefore, all optical telescopes with a diameter larger than 1.34 meters are reflecting telescopes. A larger-diameter reflecting telescope can obtain the main focus system (or Newtonian system), Cassegrain system and folding axis system by changing different secondary mirrors. In this way, a single telescope can obtain several different relative apertures and fields of view. Reflecting telescopes are mainly used for astrophysics work.
History
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 center of the primary 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 life. 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, the 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. The Hale Telescope took more than 20 years from design to completion. 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." . Before 1976, the Soviet Union built a 600-centimeter telescope, but its effect was not as good 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 needs regular coating, etc.
3. Catadioptric telescopes are based on spherical mirrors and add refractive elements for correcting aberrations, which can avoid difficult large-scale aspheric surface processing and obtain good image quality. The more famous one is the Schmidt telescope
It places a Schmidt correction plate at the center of the spherical reflector. One surface is a flat surface, and the other surface is a slightly deformed aspherical surface, which makes the central part of the beam slightly convergent and the peripheral part slightly divergent, which just corrects spherical aberration and coma. There is also a Maksutov telescope
Adding a meniscus lens in front of the spherical reflector and selecting the appropriate parameters and position of the meniscus lens can correct spherical aberration and coma at the same time. And derivatives of these two telescopes, such as super Schmidt telescope, Baker-Nunn camera, etc. In a catadioptric telescope, the image is formed by a mirror, and the refractor is used to correct aberrations. It is characterized by a large relative aperture (even greater than 1), strong light power, wide field of view, and excellent image quality. Suitable for sky survey photography and observation of nebulae, comets, meteors and other celestial objects. If a small visual telescope uses a catadioptric Cassegrain system, the lens tube can be very short.
History
The 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 correcting 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. 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.
Radio telescope
Basic equipment for detecting radio radiation from celestial bodies. It can measure the intensity, spectrum and polarization of celestial radio. Usually, it consists of three parts: antenna, receiver and terminal equipment. The antenna collects radio radiation from celestial bodies, and the receiver processes and converts these signals into a form that can be recorded and displayed. The terminal equipment records the signals, performs certain processing according to specific requirements, and then displays them. The basic indicators that characterize the performance of radio telescopes are spatial resolution and sensitivity. The former reflects the ability to distinguish radio point sources close to each other on two celestial spheres, and the latter reflects the ability to detect weak radio sources. Radio telescopes usually require high spatial resolution and high sensitivity. According to the overall structure of the antenna, radio telescopes can be divided into two categories: continuous aperture and discontinuous aperture. The main representative of the former is the classic radio telescope using a single dish parabolic antenna, while the latter is various combinations based on interference technology. Antenna system. In the 1960s, two new types of discontinuous aperture radio telescopes were produced - the very long baseline interferometer and the synthetic aperture radio telescope. The former has extremely high spatial resolution, and the latter can obtain clear radio images. The world's largest trackable classical radio telescope has a parabolic antenna with a diameter of 100 meters, installed at the Max Planck Institute for Radio Astronomy in Germany; the world's largest discontinuous aperture radio telescope is the Very Large Antenna Array, installed in the United States National Radio Astronomy Observatory.
In 1931, at Bell Labs in New Jersey, the American KG Jansky, who was responsible for searching and identifying telephone interference signals, discovered that there was a signal with a maximum value every 23 hours, 56 minutes and 4 seconds. Radio interference. After careful analysis, he concluded in an article published in 1932: This is radio radiation from the Milky Way. Thus, Jansky ushered in a new era of using radio waves to study celestial bodies.
At that time, he used a rotating antenna array 30.5 meters long and 3.66 meters high, and achieved a 30-degree wide "fan-shaped" directional beam at a wavelength of 14.6 meters. Since then, the history of radio telescopes has been one of continuous improvement in resolution and sensitivity.
Since Jansky announced that he had received radio signals from the Milky Way, American G. Leiber devoted himself to trial-producing a radio telescope, and finally succeeded in manufacturing it in 1937. This was a parabolic radio telescope that was unique in the world before World War II. Its parabolic antenna has a diameter of 9.45 meters, obtains a 12-degree "pencil-shaped" directional beam at a wavelength of 1.87 meters, and detects radio waves emitted by the sun and other celestial bodies. Therefore, Leiber is known as the founder of the parabolic radio telescope.
A radio telescope is the basic equipment for observing and studying radio waves from celestial bodies. It includes: directional antennas that collect radio waves, high-sensitivity receivers that amplify radio signals, information recording, processing and display systems, etc. . The basic principle of radio telescopes and optical reflecting telescopes is that the projected electromagnetic waves are reflected by a precise mirror and arrive at the focal point in phase. It is easy to achieve in-phase gathering by using a rotating paraboloid as a mirror surface. Therefore, most radio telescope antennas are paraboloids.
Radio observations are carried out in a wide frequency range, and the radio technology for detection and information processing is more flexible and diverse than optical waves. Therefore, there are more types of radio telescopes and various classification methods. For example, according to the shape of the receiving antenna, it can be divided into parabolic, parabolic cylinder, spherical, parabolic section, radar, spiral, traveling wave, antenna and other radio telescopes; according to the direction beam shape, it can be divided into pencil beam, fan beam, multi-beam and other radio telescopes. Telescopes; according to the purpose of observation, they can be divided into radio telescopes such as mapping, positioning, calibration, polarization, spectrum, and solar phenomena; according to the type of work, they can be divided into radio telescopes such as full power, frequency sweep, and fast imaging.
Space Telescope
A large telescope for astronomical observations outside the Earth's atmosphere. Because it avoids the influence of the atmosphere and does not cause distortion due to gravity, it can greatly improve observation capabilities and resolution capabilities, and even enable some optical telescopes to be used for near-infrared and near-ultraviolet observations. However, there are also many new strict requirements in manufacturing. For example, the mirror processing accuracy must be within 0.01 micron, and each component and mechanical structure must be able to withstand vibration and overweight during launch. However, it must be as light as possible to reduce launch costs. The first space telescope, also known as the Hubble Telescope, was launched into an orbit 600 kilometers above the ground by the U.S. Space Shuttle Discovery on April 24, 1990. It is cylindrical in shape as a whole, 13 meters long and 4 meters in diameter. The front end is the telescope part, and the rear half is the auxiliary equipment. The total weight is about 11 tons. The telescope has an effective aperture of 2.4 meters, a focal length of 57.6 meters, and an observation wavelength ranging from ultraviolet 120 nanometers to infrared 1200 nanometers. It costs US$1.5 billion. The resolution of the original design was 0.005, which was 100 times that of large ground telescopes. However, due to a small oversight in manufacturing, it was not discovered until after launch that the instrument had large spherical aberration, which seriously affected the quality of the observations. From December 2 to 13, 1993, the U.S. Space Shuttle Endeavour, carrying seven astronauts, successfully replaced 11 parts of Hubble and completed the repair work, creating the history of human repair of large spacecraft in space. The successfully repaired Hubble Telescope will continue to provide information about the depths of the universe within 10 years. In April 1991, the United States launched its second space telescope. This is a device for observing gamma rays. It weighs 17 tons, consumes 1.52 watts, and has a signal transmission rate of 17,000 bits/second. It carries 4 sets of detectors. Angular resolution is 5′～10′. Its lifespan is about 2 years.
Gemini Telescope
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 5% , Argentina accounts for 2.5, Brazil accounts for 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.
Solar Telescope
The corona is a thin, faint outer atmosphere around the sun. Its structure is complex and can only be appreciated during the short period of a total solar eclipse. , because light from the sky is always scattered or diffused into the telescope from all directions.
In 1930, the first coronagraph developed by French astronomer Leo was born. This instrument can effectively block the sun and scatter light very little, so it can be used on any day when the sun is shining. , successfully took photos of the corona. Since then, world observations of the corona have gradually emerged.
The coronagraph is only a type of solar telescope. Since the 20th century, due to the needs of actual observation, various solar telescopes have appeared, such as chromosphere telescopes, solar towers, combined solar telescopes and vacuum solar telescopes.
Infrared telescope
Infrared telescope is a telescope that receives infrared radiation from celestial bodies. The appearance and structure are similar to those of optical mirrors, and some can be used for both infrared observation and optical observation. However, when conducting infrared observation, its terminal equipment is completely different from that of optical observation. Modulation technology must be used to suppress background interference, and interference methods must be used to improve its resolution ability. Infrared observational imaging is also very different from optical images. Since the Earth's atmosphere has only seven narrow "windows" for infrared rays, infrared telescopes are often placed in high mountain areas. Most of the best ground-based infrared telescopes in the world are installed on Mauna Kea, Hawaii, USA, which is the world's research center for infrared astronomy. The Keck telescope built in 1991 is the largest infrared telescope. It has an aperture of 10 meters and can be used for both optical and infrared purposes. In addition, infrared telescopes can also be mounted on high-altitude balloons. The maximum diameter of the infrared telescope on the balloon is 1 meter, but the effect is comparable to some larger-diameter infrared telescopes on the ground.