How does science and technology affect the development of telescopes?

At the same time, the German astronomer Kepler began to study telescopes. He proposed another kind of astronomical telescope in Bending Optics, which consists of two convex lenses. Unlike Galileo's telescope, it has a wider field of vision than galileo telescope. But Kepler didn't make the telescope he introduced. Sagana first made this telescope between1613-1617. He also made a telescope with a third convex lens according to Kepler's suggestion, and turned the inverted image of the telescope composed of two convex lenses into a positive image. Sagana made eight telescopes, one for observing the sun, and no matter which one can see sunspots with the same shape. Therefore, he dispelled many people's illusion that sunspots may be caused by dust on the lens, and proved that sunspots are really observed. When observing the sun, Sagina installed special shading glass, but Galileo did not add this protective device. As a result, he hurt his eyes and finally became almost blind. Huygens of the Netherlands made a telescope with a tube length of nearly 6 meters to explore Saturn's rings in 1665, and later made a telescope with a tube length of nearly 4 1 meter. A telescope that uses a lens-cutting mirror is called a refractive telescope. Even if the lens barrel is lengthened and the lens is machined accurately, the chromatic aberration cannot be eliminated. Newton once thought that the chromatic aberration of refractive telescope was hopeless, but it turned out to be too pessimistic. 1668, he invented the reflective telescope, which solved the problem of chromatic aberration. The first reflective telescope was very small. The aperture of the mirror in the telescope was only 2.5 cm, but the profit and loss of Jupiter's satellite and Venus could be clearly seen. 1672, Newton made a larger reflecting telescope and gave it to the Royal Society, which is still kept in the library of the Royal Society. 1733, an Englishman Hal made the first achromatic refraction telescope. 1758, the same telescope was made in Boland, London. He made convex lenses and concave lenses from glasses with different refractive indexes to offset the colored edges they formed. However, it is not easy to make a big shot. At present, the largest refracting telescope in the world has a diameter of 102 cm and is installed at the Addis Observatory. Monoscope 1793 British William Herschel made a reflective telescope. The reflector has a diameter of 130 cm, is made of copper-tin alloy and weighs 1 ton. The reflecting telescope made in william parsons, England in 1845, the diameter of the reflector is1.82m .. 19 17, and the Hooke telescope was built at Mount Wilson Observatory in California, USA. Its primary mirror aperture is 100 inch. It was with this telescope that Edwin Hubble discovered the amazing fact that the universe is expanding. 1930, BernhardSchmidt, Germany, combines the advantages of refractive telescope and reflecting telescope (refractive telescope has small aberration but chromatic aberration, and the larger the size, the more expensive it is; Reflective telescope has no chromatic aberration, and its cost is low. The reflector can be made large, but there is chromatic aberration), and the first folding reflective telescope is made. After the war, reflective telescopes developed rapidly in astronomical observation. 1950, Haier reflective telescope with a diameter of 5.08m was installed on the Paloma Mountain. 1969, a reflector with a diameter of 6 meters was installed on Pastuhov Mountain in the North Caucasus of the former Soviet Union. 1990, NASA put the Hubble Space Telescope into orbit. However, due to the mirror failure, the Hubble Space Telescope didn't play its full role until 1993 astronauts completed the space repair and replaced the lens. Because it can not be disturbed by the earth's atmosphere, the image clarity of Hubble telescope is 10 times that of similar telescopes on earth. 1993, the Keck telescope with a diameter of 10 meter was built in Monaque Mountain, Hawaii, and its mirrors were composed of 36 mirrors with a diameter of 1.8 meter. 200 1 the European southern observatory in Chile has developed the "VLT", which consists of four 8-meter-diameter telescopes, and its light-gathering capacity is equivalent to one 16-meter reflective telescope. Now, a number of telescopes under construction have begun to attack the White Giant brothers on Mount Monaque. These new competitors include the California Giant Telescope (CELT) with a diameter of 30m, the Giant Magellanic Telescope (GMT) with a diameter of 20m and the Overwhelming Telescope (OWL) with a diameter of 100m. Their supporters point out that these new telescopes can not only provide space pictures with far better image quality than Hubble, but also collect more light, learn more about the initial stars and cosmic gases when galaxies formed 654.38 billion years ago, and clearly see the planets around distant stars.

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 there was a climax of manufacturing large-aperture refractive telescopes. 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.

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.

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.