Seek knowledge about astronomical telescopes

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.

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.

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.

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

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.

Gemini telescope (Gemini)

Gemini telescope is an international equipment led by the United States (50% in the United States, 25% in Britain, 5% in Canada, 5% in Chile, 2.5% in Argentina and 2.5% in Brazil), which 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.

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.

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.

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.

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.

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.

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.