Principle of operation and structure of optical and radio telescope methods. Antennas not for communication: the world's largest radio telescope

The main purpose of telescopes is to collect as much emission from the heavenly body. This allows you to see non-latch objects. In second place, telescopes serve to view objects at a large angle or, as they say, to increase. Resolution small details - Third purpose of telescopes. The amount of light-generated light and the available permission of parts strongly depends on the area of \u200b\u200bthe main part of the telescope - its lens. Lens are mirror and lenzov.

Lenzovy telescopes.

Lenses, one way or another, are always used in the telescope. But in the refractors-refractors lens is the main detail of the telescope - its lens. Recall that refraction is a refraction. The lens lens refracts the rays of light, and collects them at a point, called the focus of the lens. At this point, an image of an object of study is built. To consider it use the second lens - eyepiece. It is placed so that the focus of the eyepiece and the lens coincide. Since the vision of people is different, then the eyepiece make moving to make it possible to achieve a clear image. We call it the sharpness setting. All telescopes have unpleasant features - aberrations. Aberrations are distortions that are obtained by passing light through the optical system of the telescope. The main aberrations are associated with the imperfection of the lens. Lens telescopes (and telescopes in general) sin with several aberrations. Let's call only two of them. The first is connected with the fact that rays different lengths Waves refracted a little differently. Because of this, there is one focus for blue rays, and for the red - the other, located on the lens. The rays of other wavelengths are gathering each in their place between these two focus. As a result, we see the objects painted in the rainbow. Such an aberration is called chromatic. The second strong aberration is spherical aberration. It is connected with the fact that the lens, the surface of which is part of the sphere, in fact, does not collect all the rays at one point. Rays running at different distances from the center of the lens are collected at different points, which is why the image is fuzzy. This aberration would not have if the lens had the surface of the paraboloid, but it was difficult to make such a detail. To reduce aberrations are made of complex, not double-lit-in systems. Additional parts are introduced to correct the aberration of the lens. The long-standing championship among lenzov telescopes is a telescope of the Jerk Observatory with a lens 102 centimeter with a diameter.

Mirror telescopes.

At ordinary mirror telescopes, reflector telescopes, the lens is a spherical mirror that collects light rays and reflects them with the help of an additional mirror towards the eyepiece - lenses, in the focus of which the image is built. Reflex is a reflection. Mirror telescopes do not sin chromatic aberration, as the light in the lens is not refracted. But the reflectors are stronger than the spherical aberration, which, by the way, strongly limits the field of view of the telescope. In mirror telescopes, complex structures are also used, the surfaces of mirrors other than spherical and so on.

Mirror telescopes make it easier and cheaper. That is why their production in recent decades is growing rapidly, while new major lenzov telescopes have not been done for a very long time. The largest mirror telescope has a complex lens from several mirrors equivalent to a whole mirror with a diameter of 11 meters. The largest monolithic mirror lens has a size a little more than 8 meters. The biggest optical telescope of Russia is a 6-meter mirror telescope BTA (a large azimuth telescope). The telescope for a long time was the largest in the world.

Characteristics of telescopes.

Increased telescope. An increase in the telescope is equal to the ratio of the focus distances of the lens and the eyepiece. If, say, the focal length of the lens is two meters, and the eyepiece is 5 cm, then the increase in such a telescope will be 40 times. If you change the eyepiece, you can change and increase. So astronomers come, because not to change, in fact, a huge lens?!

Output pupil. An image that builds an eyepiece for the eye can generally be both more eye pupil and less. If the image is larger, then some of the light into the eye will not fall, thereby, the telescope will be used not 100%. This image is called an output pupil and calculated by the formula: p \u003d d: w, where P is the output pupil, D is the diameter of the lens, and W is an increase in the telescope with such an eyepiece. If you take the size of the eye pupil equal to 5 mm, it is easy to calculate the minimum increase, which is reasonable to use with this lens of the telescope. We obtain this limit for a lens of 15 cm: 30 times.

The resolution of telescopes

Since the light is a wave, and the waves are characteristic not only the refraction, but also diffraction, no, even the most perfect telescope gives an image of a point star in the form of a point. The perfect image of the star looks like a disk with several concentric (with a common center) rings that are called diffraction. The size of the diffraction disk and the resolution of the telescope is limited. All that closes this disc, you will not see in this telescope. The angular size of the diffraction disk in the state of the arc for this telescope is determined from the simple relation: R \u003d 14 / d, where the diameter D of the lens is measured in centimeters. Mentioned just above the fifteenisantimeter telescope has a limiting resolution of a little less than a second. It follows from the formula that the resolution of the telescope is entirely depends on the diameter of its lens. Here is another reason for the construction of as many grant telescopes as possible.

Relative hole. The ratio of the diameter of the lens to its focal length is called the relative hole. This parameter determines the lens of the telescope, i.e., rudely speaking, its ability to display objects bright. Lenses with a relative hole 1: 2 - 1: 6 are called high-tear. They are used to photograph the weak brightness of objects, such as nebulae.

Telescope without eyes.

One of the most unreliable details of the telescope has always been an eye of the observer. Each person has their own eyes, with their own characteristics. One eye sees more, the other is less. Each eye sees color in different ways. Human eye and his memory are not able to preserve the whole picture offered for the contemplation by a telescope. Therefore, as soon as it became possible, astronomers began to replace the eye to the instruments. If you subscribe instead of eyepiece the camera, then the image obtained by the lens can be captured on the photographic or film. Photoplastic is capable of accumulating light radiation, and this is an indisputable and important advantage over the human eye. Highly exposure photos are capable of displaying incomparably more than to consider man into the same telescope. And of course, the photo will remain as a document to which it will be repeatedly possible to appeal. Even more modern tool are the CCD - cameras with polar-charge ties. These are photosensitive chips that replace the photoplastic and transmit accumulated information on the computer, and then can make a new shot. The spectra of stars and other objects are investigated using spectrographs and spectrometers attached to the telescope. No eye is able to clearly distinguish between the colors and measure the distances between the lines in the spectrum, as it can easily make these devices that also retain the image of the spectrum and its characteristics for subsequent studies. Finally, no one can see one eye into two telescope at the same time. Modern systems of two or more telescopes, combined with one computer and spaced, sometimes at tens of meters, allow you to achieve amazingly high permissions. Such systems are called interferometers. An example of a system of 4 telescopes - VLT. As many as four types of telescopes, we combined into one subsection noble. The earth's atmosphere passes the corresponding lengths of electromagnetic waves reluctantly, so telescopes for studying the sky in these ranges tend to bring into space. It is with the development of cosmonautics that the development of ultraviolet, x-ray, gamma and infrared sectors of astronomy is directly connected.

Radio telescopes.

As a radio telescope lens, the metal cup of paraboloid form is most often. The signal collected by it is taken an antenna in the focus of the lens. Antenna is associated with a computer that usually processes all the information, building images in conventional colors. The radio telescope, like the radio, is able to simultaneously take only some kind of wavelength. In the book B. A. Vorontsova-Veljaminov "Essays about the Universe" there is a very interesting illustration, directly related to the subject of our conversation. In one observatory, guests were offered to approach the table and take a piece of paper from it. The man took a piece of leaf and on the back of the following: "Taking this piece of paper, you spent more energy than all the world's radioskops accepted for the entire existence of radio astronomy." If you familiarize yourself with this section (and should), then you must remember that radio waves have the largest wavelengths among all types of electromagnetic radiation. This means that the photons corresponding to radio waves carry quite a bit of energy. To collect an acceptable amount of information about the luminars in radars, astronomers build huge telescopes. Hundreds of meters - that's not so much an amazing frontier for the diameters of the lenses that will be achieved modern science. Fortunately, everything in the world is interconnected. The construction of giant radio telescope is not accompanied by the same difficulties in the processing of the lens surface, which are inevitable in the construction of optical telescopes. The permissible surface errors are proportional to the wavelength, therefore, sometimes, the metal bowls of radio telescopes are not smooth surface, but simply the grid, and this does not affect the quality of the reception. A large wavelength also allows you to build a grandiose system of interferometers. Sometimes, telescopes of different continents participate in such projects. In projects there are space-scale interferometers. If they come true, radio astronomy will reach unprecedented limits in the resolution of heavenly objects. In addition to collecting radiation heavenly bodies Energy, radio telescopes available "highlighting" the surface of the body of the solar system radioles. The signal sent, let's say from the ground to the moon, will reflect from the surface of our satellite and will be accepted by the same telescope as the signal sent. This research method is called radar. Using radar, you can find out a lot. For the first time, astronomers learned that Mercury rotates around its axis in this way. The distance to objects, the speed of their movement and rotation, their relief, some data on the chemical composition of the surface - these are the ongoing information that by the forces to find out with radar methods. The most ambitious example of such studies is complete mapping of the surface of Venus, conducted by AMC "Magellan" at the junction of the 80s and 90s. As you may be, you know, this planet hides from the human eye its surface behind a dense atmosphere. Radio waves are freely pass through the clouds. Now we know about the relief of Venus better than about the relief of the Earth (!), After all, on Earth, the ocean covers prevents the study of most of the solid surface of our planet. Alas, the speed of propagation of radio waves is large, but not limitless. In addition, with the remoteness of the radio telescope from the object, the dispersion of the sent and reflected signal increases. At the distance, Jupiter-Earth signal is already difficult to accept. Radar - in astronomical standards, melee weapons.

FGBOU VPO "Taganrog State Pedagogical Institute named after A.P. Chekhov "

Radio astronomy. Radio telescopes.

Main characteristics.

Performed student

faculty of Physics and Mathematics

51 groups: Mazur V.G.

Taganrog

Introduction

Radio astronomy is a section of astronomy, which studies space objects by analyzing radio emission coming from them. Many cosmic bodies emit radio waves reaching the Earth: this, in particular, the external layers of the sun and the atmosphere of the planets, the clouds of interstellar gas. Radioisuction accompanies such phenomena as the interaction of turbulent gas flows and shock waves in the interstellar medium, the rapid rotation of neutron stars with a strong magnetic field, "explosive" processes in galaxies and quasar nuclei, solar flashes etc. Radio signals of natural objects coming to Earth have noise. These signals are accepted and enhanced using special electronic technology, and then recorded in analog or digital form. Often, radio astronomy technique is more sensitive and long-range than optical.

The radio telescope is an astronomical tool for receiving its own radio emission of celestial objects (in the entire system, the galaxy and metagalaxy) and the study of their characteristics, such as: coordinates, spatial structure, radiation intensity, spectrum and polarization.

Radio astronomy

§1. Creation with optical astronomy

Of all the types of space electromagnetic radiation to the surface of the earth, through its atmosphere, there are practically no weakening, only visible lightClose (shortworn) infrared radiation and part of the radio wave spectrum. On the one hand, radio waves, having a much greater wavelength than optical radiation, easily pass through the cloud atmosphere of planets and clouds of interstellar dust, opaque for light. On the other hand, only the shortest radio waves pass through transparent areas of ionized gas around the stars and in the interstellar space. Weak radio astronomer spaces are tracked using radio telescope, the main elements of which are antenna. This is usually metal reflectors in the form of a paraboloid. In the focus of the reflector, where the radiation concentrates is concentrated, the collecting device is placed in the form of a horn or dipole, which removes the collected radio emission to the receiving equipment. Reflectors with a diameter of up to 100 m are made of movable and full-time; They can induce the object in any part of the sky and follow it. Larger reflectors (up to 300 m in diameter) are fixed, in the form of a huge spherical bowl, and targeting an object occurs due to the rotation of the Earth and moving the irradiator in the focus of the antenna. Reflectors are still more sized usually have a part of a paraboloid part. The larger the size of the reflector, the more detailed the observed radiocartine. Often, for its improvement, one object is observed synchronously with two radio telescope or their integer system containing several dozen antennas, sometimes spaced by thousands of kilometers.

§2. Ranges of registered radio emission

Through earthly atmosphere Radio waves are underway with a length of several millimeters to 30 m, i.e. in the frequency range from 10 MHz to 200 GHz. Thus, radio astronomers are dealing with frequencies noticeably higher than, for example, a broadcast radio range of medium or short waves. However, with the appearance of VHF and television broadcasting in the frequency range of 50-1000 MHz, as well as radar (radars) in the range of 3-30 GHz, problems occurred: the powerful signals of the earth transmitters in these ranges interfere with the reception of weak space signals. Therefore, through international agreements, radio astronomers are allocated to monitor the space of several frequency ranges in which the transmission of signals is prohibited.

§3. Historical reference

Radio astronomy as science has begun in 1931, when K.Yansky from Belle Phone began to study the interference of radio communications and found that they come from the central part Milky Way. The first radio telescope was built in 1937-1938 Radiogerer Greater, who independently made a 9-meter reflector in his garden from the iron sheets, basically the same as the current giant parabolic antennas. The ribs was the first radiocar of the sky and found that the entire Milky Way radiates on the wave of 1.5 m, but its central part is most. In February 1942, J. Say noticed that in a meter range the sun creates interference with radar, when flashes occur on it; The Sun radio emission in the centimeter range in 1942-1943 was discovered by J. Souther. The systematic development of radio astronomy began after World War II. In the UK, a large Observatory of Jodrell-Bank (Manchester University) and the Station of the Cavendish Lab (Cambridge) were created. Radiophysical laboratory (Sydney) organized several stations in Australia. Netherlands radio astronomers began to study the clouds of interstellar hydrogen. In the USSR, radio telescopes were built under the Serpukhov, in Pulkovoy, in the Crimea. The largest radio operators of the United States are the national radio astronomy observatory in Green Bank (PC. Zap.Viginia) and Charlottersville (PC. Virginia, Observatory of Cornell University in Arecibo (O. Puerto Rico), Observatory of the California Institute of Technology in Owens-Valley (PC. California), Lincoln Laboratory of the Massachusetts Institute of Technology and Observatory Ok-Ridge Harvard University (PC. Massachusetts), Observatory of Hat-Creek California University in Berkeley (California), Radio astronomy Observatory of the five colleges of the University of Massachusetts (PC. Massachusetts).

Radi-telescopes

The radio telescope occupies the initial, according to the frequency range, the position among astronomical instruments for the study of electromagnetic radiation. More high-frequency telescopes of thermal, visible, ultraviolet, X-ray and gamma radiation are higher.

Radi-telescopes preferably have far from the main settlements in order to maximize the electromagnetic interference from broadcast radio stations, television, radars and other radiating devices. The placement of the radio operator in the valley or lowline even better protects it from the influence of man-made electromagnetic noises.

The radio telescope consists of two main elements: an antenna device and a very sensitive receiving device - a radiometer. Radiometer enhances the received antenna radio emission, and converts it into a form, convenient for registration and processing.

The designs of the antennas of radio telescope are distinguished by a large variety, which is due to a very wide range of wavelengths used in radio astronomy (from 0.1 mm to 1000 m). The antennas of radio telescope taking MM, CM, DM and meter waves are most often parabolic reflectors like mirrors of conventional optical reflectors. In the focus of the paraboloid, the irradiator is installed - a device collecting radio emission, which is sent to it with a mirror. The irradiator transmits the accepted energy to the input of the radiometer, and, after amplification and detection, the signal is recorded on the tape of the self-sample electrical meter. On modern radio telescope analog signal From the output of the radiometer is converted into digital and recorded on hDD in the form of one or more files.

To direct the antennas to the studied area of \u200b\u200bthe sky, they are usually set on azimuth mounts that provide turns in azimuth and height (full-turn antennas). There are also antennas that allow only limited turns, and even completely fixed. The direction of acceptance in the antennas of the last type (usually very large) is achieved by moving the irradiators that perceive the radio emission reflected from the antenna.

§four. Principle of operation

The principle of the radio telescope is more similar to the principle of the photometer, rather than an optical telescope. The radio telescope cannot build an image directly, it only measures the radiation energy coming from the direction in which the telescope looks at. Thus, in order to obtain an image of an extended source, the radio telescope should measure its brightness at each point.

Due to the diffraction of radio waves on the telescope aperture, the direction measurement on the point source occurs with a certain error, which is determined by the antenna pattern and imposes a fundamental restriction on the resolution of the tool:

where - the wavelength is the diameter of the aperture. High resolution allows you to observe smaller spatial details of the objects under study. To improve the resolution, you need to either reduce the wavelength, or increase the aperture. However, the use of low wavelengths increases the quality requirements of the mirror surface (see the Relay Criterion). Therefore, usually go along the way to increase the aperture. An increase in aperture also allows you to improve another important characteristic - sensitivity. The radio telescope must have a high sensitivity to ensure reliable registration as weaker sources as possible. Sensitivity is determined by the level of flow density fluctuations:

,

where - the power of their own noise of the radio telescope is an effective area (collecting surface) antenna, - the frequency band and the signal accumulation time. To increase the sensitivity of radio telescope, they increase their collecting surface and use low-noise receivers and amplifiers based on maters, parametric amplifiers, etc.

§five. Radio interferometers

In addition to increasing the diameter of the aperture, there is another way to increase the resolution (or narrow the radiation diagram). If you take two antennas located at a distance d. (base) from each other, the signal from the source to one of them will come a little earlier than before the other. If then the signals from two antennas to be interfered, then from the resulting signal using a special mathematical reduction procedure, you can restore information about the source with effective resolution. Such a reduction procedure is called aperture synthesis. Interference can be carried out as hardware, by means of signaling the signal over cables and waveguides into a common mixer and on a computer with a previously digitized by the exact time and stored signals stored on the carrier. Modern technical means allowed to create a RSDB system, which includes telescopes located on different continents and separated by several thousand kilometers.

§6. First radio telescopes

Beginning - Karl Yansky

Copy of radio telescopeJansky

History radi-Telececopes He takes his beginning in 1931, from the experiments of Karl Yansky at the BELL TELEPHONE LABS polygon. To study the direction of the arrival of thunder interference, it built a vertically polarized unidirectional antenna of the Bruce blade. The design dimensions were 30.5 m in length and 3.7 m in height. The work was carried out on a wave of 14.6 m (20.5 MHz). The antenna was connected to a sensitive receiver, at the exit of which the recorder stood with a large time constant.

Record the radiation received by Yansky February 24, 1932. Maxima (arrows) are repeated after 20 minutes. - Period of full turnover of antenna.

In December 1932, Jansky had already reported on the first results obtained at its installation. The article reported the detection of "... permanent hissing of unknown origin", which "... It is difficult to distinguish from the hiss caused by the noise of the equipment itself. The direction of the arrival of hissing interference changes gradually during the day, making a full turn in 24 hours. " In the two following works, in October 1933 and October 1935, Karl Yansky gradually comes to the conclusion that the source of its new interference is the central region of our galaxy. Moreover, the greatest response is obtained when the antenna is directed to the center of the Milky Way.

Jansky realized that progress in radio astronomy would require antennas large sizes With more acute charts that need to be easily orientable in various directions. He himself suggested the design of a parabolic antenna with a mirror of 30.5 m in diameter to work on meter waves. However, his proposal did not receive support in the United States.

Second birth - ribs

Meridian radio telescopeGrew repetition

In 1937, the ribs, Waton's Radio Engineer (USA, Illinois) became interested in the work of the Yansky and designed in the backyard houses of his parents antenna with a parabolic reflector with a diameter of 9.5 m. This antenna had a meridian mount, that is, it was managed only at the corner of the place , and the change in the position of the petal of the diagram on direct ascent was achieved due to the rotation of the Earth. The antenna of the edges was less than the Yansky, but worked on shorter waves, and its radiation diagram was significantly sharper. At the antenna, the rabes raise had a conical shape with a 12 ° width over half of the power, while the yoke antenna beam was a fan-shaped form of a width of 30 ° in terms of half-power in the most narrow section.

In the spring of 1939, the ribs discovered 1.87 m (160 MHz) radiation with a noticeable concentration in the plane of the galaxy and published some results.

Radio Skin Card receivedGround ribrom In 1944

Improving its equipment, the ribs took the systematic review of the sky and in 1944 published the first radiocards of the sky at a wave of 1.87 m. On the maps, the central regions of the Milky Way and bright radio sources in the constellation are clearly visible in the constellation, Swan A, Cassiopeia A, Big PSA and Cord. Cards of ribs are good enough even compared to modern cards, meter wavelengths.

After World War II, substantial technological improvements in the field of radio astronomy scientists in Europe, Australia and the United States were made. Thus, the flourishing of radio astronomy began, which led to the development of millimeter and submillimeter wavelengths, allowing to achieve significantly large permits.

§7. Classification of radio telescope

A wide range of wavelengths, a variety of research objects in radio astronomy, the rapid pace of radiophysics and radio equipment, a large number of independent radio astronomer teams led to a wide variety of radio telescope types. It is most natural to classify radio telescopes in the nature of the filling of their aperture and according to the methods of microwave fields (reflectors, refractors, independent field entry)

Antennas with filled aperture

The antennas of this type are similar to the mirrors of optical telescopes and is the most simple and familiar to use. Antennas with a filled aperture simply collect a signal from the observed object and focus it on the receiver. The recorded signal also carries scientific information and does not need synthesis. The disadvantage of such antennas is low resolution. Antennas with unfilled aperture can be divided into several classes in the form of their surface and the mount method.

Paraboloids of rotation

Almost all the antennas of this type are mounted on alt-azimuthal mothings and are full-turn. Their main advantages are that such radio telescopes can, as well as optical, to induce the object and lead it. Thus, observations can be carried out at any time as long as the object under study is above the horizon. Typical representatives: Green-Bank radio telescope, RT-70, Kalyazin radio telescope.

Parabolic cylinders

The construction of full-time antennas is associated with certain difficulties associated with a huge mass of such structures. Therefore, build fixed and semi-motivable systems. The cost and complexity of such telescopes is growing much slower with their growing size. The parabolic cylinder collects rays not at the point, but on a straight line parallel to its forming (focal line). Because of this telescopes this type Have an asymmetric pattern of focus and various resolution on different axes. Another disadvantage of such telescopes is that only part of the sky is available in view of the limited mobility for observation. Representatives: Radiothers Illinois University, Indian Telescope in the UTI.

The course of the rays in the NASE telescope

Antennas with flat reflectors

To work on a parabolic cylinder, it is required that several detectors are placed on the focal line, the signal from which it takes into account the phases. On short waves it is not easy because of the large losses in the communication lines. Flat reflector antennas allow only one receiver to do. Such antennas consist of two parts: a movable flat mirror and a fixed paraboloid. The movable mirror "is guided" to the object and reflects the rays on the paraboloid. A paraboloid concentrates the rays at the focus point where the receiver is located. This telescope is only available part of the sky for observations. Representatives: Kraus radio telescope, a large radio telescope in NASE.

Earthy bowls

The desire to reduce the cost of led astronomers to the thoughts on the use of natural relief as a telescope mirror. The representative of this type was the 300-meter radio telescope Arecibo. It is located in the karst funnel, the bottom of which is paved by aluminum sheets in the form of spheroid. A receiver on special supports is suspended above the mirror. The disadvantage of this tool is that he is available to the sky area within 20 ° from the zenith.

Antenna lattices (syphase antennas)

Such a telescope consists of a plurality of elementary irradiators (dipoles or spirals) located at a distance of less than the wavelength. Thanks to the accurate phase control of each element, it is possible to achieve a high resolution and effective area. The disadvantage of such antennas is that they are manufactured under a strictly defined wavelength. Representatives: BSA radio telescope in Pushchino.

Antennas with unfilled aperture

The most important for the purposes of astronomy are two characteristics of radio telescope: resolution and sensitivity. In this case, the sensitivity is proportional to the area of \u200b\u200bthe antenna, and the resolution is the maximum size. Thus, the most common round antennas give worst permission with the same efficient area. Therefore, telescopes with small appeared in radio astronomy

DKR-1000 telescope, with unfilled aperture

square, but large resolution. Such antennas were named antennas with unfilled apertureSince they have "holes" in aperture, superior to the wavelength. To obtain an image from such antennas, observations need to be carried out in the synthesis of apertures. For aperture synthesis, two synchronously working antennas located at some distance called base. To restore the source image, you need to measure the signal at all possible bases with some step up to the maximum.

If the antennas are only two, you will have to monitor, then change the database, to monitor the next point, change the database again, etc. Such synthesis is called consistent. This principle works a classic radio interferometer. The disadvantage of serial synthesis is that it requires a lot of time and cannot identify the variability of radio sources on short times. Therefore, it is more often used parallel synthesis. It takes directly a lot of antennas (receivers), which simultaneously perform measurements for all necessary bases. Representatives: "Northern Cross" in Italy, DKR-1000 radio telescope in Pushchino.

Large arrays of the VLA type are often referred to as a sequential synthesis. However, in view of large number Antennas, almost all bases are already presented, and additional permutations are usually not required.

List of radio telescope.

Bibliography

1. Cosmos physics: small. ENT., 1986, p. 533.

2. Kaplan S. A. As radio astronomy arose // Elementary radio astronomy. - M.: Science, 1966. - C. 12. - 276 p.

3. 1 2 Kraus D. D. 1.2. Short story The first years of radio astronomy // Radio Astronomy / Ed. V.V. Zheleznyakova. - M.: Soviet radio, 1973. - P. 14-21. - 456 p.

4. Big Soviet Encyclopedia. - USSR: Soviet Encyclopedia, 1978.

5. Electromagnetic radiation. Wikipedia.

6. Radi-telescope // Cosmos Physics: Little Encyclopedia / Ed. R. A. Syunayeva. - 2nd ed. - M.: OV. Encyclopedia, 1986. - P. 560. - 783 p. - ISBN 524 (03)

7. P.I. Bakulin, E.V. Kononovich, V.I. Morozoz Course general Astronomy. - M.: Science, 1970.

8. 1 2 3 4 John D. Kraus. Radio astronomy. - M.: Soviet radio, 1973.

9. Jansky K.G. Directional Studies of Atmospherics at Hight Frequencies. - Proc. Ire, 1932. - T. 20. - P. 1920-1932.

10. Jansky K.G. Electrical Disturbances Apparently of Extraterrestrial Origin .. - Proc. Ire, 1933. - T. 21. - P. 1387-1398.

11. Jansky K.G. A Note On The Source of Interstellar Interference .. - Proc. Ire, 1935. - T. 23. - P. 1158-1163.

12. Reber G. Cosmic Static. - Astrophys. J., June, 1940. - T. 91. - P. 621-624.

13. Reber G. Cosmic Static. - Proc. Ire, FEBruary, 1940. - T. 28. - P. 68-70.

14. 1 2 Reber G. Cosmic Static. - Astrophys. J., NovEmber, 1944. - T. 100. - P. 279-287.

15. Reber G. Cosmic Static. - Proc. Ire, August, 1942. - T. 30. - P. 367-378.

16. 1 2 N.A.Sepkin, D.V. Korolkov, Yu.N.Pariysky. Radio telescopes and radiometers. - M.: Science, 1973.

17. RadiTelacescope Illinois University.

18. 1 2 L. M. Gindilis "SETI: Search for extraterrestrial mind"

In the valley or lowland, it also protects it even better from the influence of man-made electromagnetic noises.

Device

The radio telescope consists of two main elements: an antenna device and a very sensitive receiving device - a radiometer. The radiometer enhances the adopted antenna radio emission and converts it to a form, convenient for registration and processing.

The designs of the antennas of radio telescope are distinguished by a large variety, which is due to a very wide range of wavelengths used in radio astronomy (from 0.1 mm to 1000 m). The antennas of radio telescope taking MM, CM, DM and meter waves are most often parabolic reflectors like mirrors of conventional optical reflectors. In the focus of the paraboloid, the irradiator is installed - a device collecting radio emission, which is sent to it with a mirror. The irradiator transmits the accepted energy to the input of the radiometer, and, after amplification and detection, the signal is recorded on the tape of the self-sample electrical meter. On modern radio telescopes, an analog signal from the radiometer exit is converted into digital and written to a hard disk in the form of one or more files.

To calibrate the measurements obtained (bringing them to absolute torque density values \u200b\u200bof the radiation stream) to the input of the radiometer instead of the antenna, the noise generator of the known power is connected: 535.

Depending on the design of the antenna and the methods of observations, the radio telescope can either prepare in advance on setpoint The heavenly sphere (through which the observed object will pass due to the daily rotation of the Earth), or work in tracking mode.

To direct the antennas to the studied area of \u200b\u200bthe sky, they are usually set on azimuth mounts that provide turns in azimuth and height (full-turn antennas). There are also antennas that allow only limited turns, and even completely fixed. The direction of acceptance in the antennas of the last type (usually very large) is achieved by moving the irradiators that perceive the radio emission reflected from the antenna.

Principle of operation

The principle of the radio telescope is more similar to the principle of the photometer, rather than an optical telescope. The radio telescope cannot build an image directly, it only measures the radiation energy coming from the direction in which the telescope looks at. Thus, in order to obtain an image of an extended source, the radio telescope should measure its brightness at each point.

Due to the diffraction of radio waves on the telescope aperture, the measurement of the direction to the point source occurs with a certain error, which is determined by the antenna pattern of the orphanage and imposes a fundamental restriction on the resolution of the tool:

where λ (\\ displaystyle \\ lambda) - wavelength, D (\\ DisplayStyle D) - diameter of aperture. High resolution allows you to observe smaller spatial details of the objects under study. To improve the resolution, you need to either reduce the wavelength, or increase the aperture. However, the use of low wavelengths increases the quality requirements of the mirror surface (see the Relay Criterion). Therefore, usually go along the way to increase the aperture. An increase in aperture also allows you to improve another important characteristic - sensitivity. The radio telescope must have a high sensitivity to ensure reliable registration as weaker sources as possible. Sensitivity is determined by the level of flow density fluctuations Δ P (\\ DisplayStyle \\ Delta P):

where P (\\ DisplayStyle P) - power of own noise of radio telescope, S A (\\ DisplayStyle S_ (A)) - effective antenna area, Δ F (\\ DisplayStyle \\ Delta F) - frequency band and T (\\ DisplayStyle T) - Signal accumulation time. To increase the sensitivity of radio telescope, they increase their collecting surface and low-noise receivers and amplifiers based on maters, parametric amplifiers, and so on.

Radio interferometers

In addition to increasing the aperture, there is another way to increase the resolution (or narrow the radiation diagram). If you take two antennas located at a distance D (\\ DisplayStyle D) (base) from each other, the signal from the source to one of them will come a little earlier than before the other. If then the signals from two antennas to be interfered, then from the resulting signal using a special mathematical reduction procedure, you can restore information about the source with effective resolution. λ / d (\\ displaystyle \\ lambda / d). Such a reduction procedure is called aperture synthesis. Interference can be carried out as hardware, by means of signaling the signal over cables and waveguides into a common mixer and on a computer with a previously digitized by the exact time and stored signals stored on the carrier. Modern technical means allowed to create a RSDB system, which includes telescopes located on different continents and separated by several thousand kilometers.

First radio telescopes

Beginning - Karl Yansky

The history of radio telescope takes its beginning in 1931, from the experiments of Karl Yansky at the BELL TELEPHONE LABS polygon. To study the direction of the arrival of thunder interference, it built a vertically polarized unidirectional antenna of the Bruce blade. The design dimensions were 30.5 m in length and 3.7 m in height. The work was carried out on a wave of 14.6 m (20.5 MHz). The antenna was connected to a sensitive receiver, at the exit of which the recorder stood with a large time constant.

Jansky was aware that progress in radio astronomy would require large-sized antennas with more acute charts that should be easily orientable in various directions. He himself suggested the design of a parabolic antenna with a mirror of 30.5 m in diameter to work on meter waves. However, his proposal did not receive support in the United States.

Second birth - ribs

Improving its equipment, the ribs took the systematic review of the sky and in 1944 published the first radiocards of the sky at a wave of 1.87 m. On the maps, the central regions of the Milky Way and bright radio sources in the constellation are clearly visible in the constellation, Swan A, Cassiopeia A, Big PSA and Cord. The edges' cards are quite good even compared to modern maps of meter wavelengths.

Antennas with filled aperture

Parabolic cylinders

The construction of full-time antennas is associated with certain difficulties associated with a huge mass of such structures. Therefore, build fixed and semi-motivable systems. The cost and complexity of such telescopes is growing much slower with their growing size. The parabolic cylinder collects rays not at the point, but on a straight line parallel to its forming (focal line). Because of this, the telescopes of this type have an asymmetric diagram of the orientation and various resolution on different axes. Another disadvantage of such telescopes is that only part of the sky is available in view of the limited mobility for observation. Representatives: Radiothers Illinois University, Indian telescope in the UTI.

Antennas with flat reflectors

To work on a parabolic cylinder, it is required that several detectors are placed on the focal line, the signal from which it takes into account the phases. On short waves it is not easy because of the large losses in the communication lines. Flat reflector antennas allow only one receiver to do. Such antennas consist of two parts: a movable flat mirror and a fixed paraboloid. The movable mirror "is guided" to the object and reflects the rays on the paraboloid. A paraboloid concentrates the rays at the focus point where the receiver is located. This telescope is only available part of the sky for observations. Representatives: Kraus radio telescope, a large radio telescope in NASE.

Earthy bowls

The desire to reduce the cost of led astronomers to the thoughts on the use of natural relief as a telescope mirror. The representative of this type was the 300-meter radio telescope Arecibo. It is located in the karst funnel, the bottom of which is paved by aluminum sheets in the form of spheroid. A receiver on special supports is suspended above the mirror. The disadvantage of this tool is that he is available to the sky area within 20 ° from the zenith.

Antenna lattices (syphase antennas)

Such a telescope consists of a plurality of elementary irradiators (dipoles or spirals) located at a distance of less than the wavelength. Thanks to the accurate phase control of each element, it is possible to achieve a high resolution and effective area. The disadvantage of such antennas is that they are manufactured under a strictly defined wavelength. Representatives: BSA radio telescope in Pushchino.

Antennas with unfilled aperture

The most important for the purposes of astronomy are two characteristics of radio telescope: resolution and sensitivity. In this case, the sensitivity is proportional to the area of \u200b\u200bthe antenna, and the resolution is the maximum size. Thus, the most common round antennas give worst permission with the same efficient area. Therefore, telescopes appeared in radio astronomy small squarebut great resolution. Such antennas were named antennas with unfilled apertureSince they have "holes" in aperture, superior to the wavelength. To obtain an image from such antennas, observations need to be carried out in the synthesis of apertures. For aperture synthesis, two synchronously working antennas located at some distance called base. To restore the source image, you need to measure the signal at all possible bases with some step up to the maximum.

If the antennas are only two, you will have to monitor, then change the database, to monitor the next point, change the base and so on. Such synthesis is called consistent. This principle works a classic radio interferometer. The disadvantage of serial synthesis is that it requires a lot of time and cannot identify the variability of radio sources at short times. Therefore, it is more often used parallel synthesis. It takes directly a lot of antennas (receivers), which simultaneously perform measurements for all necessary bases. Representatives: "Northern Cross" in Italy, DKR-1000 radio telescope in Pushchino.

Large arrays of the VLA type are often referred to as a sequential synthesis. However, due to the large number of antennas, almost all bases are already presented, and additional permutations are usually not required.

List of largest radio telescope

The photo shows the Merchason radio astronomy observatory, which is located in Western Australia. It includes 36 complexes with such mirror antennas operating in the range of 1.4 GHz. The diameter of the main mirror of each antenna is 12 meters. Together, these antennas are part of a large Pathfinder radio telescope. This is the largest radio telescope for today.

Tens of mirror antennas are used for research and observation of the galaxy. They are able to look into such a distance, which is not capable of the world's largest optical Hubble telescope. Together, these antennas work as one large interferometer and form an array capable of collecting electromagnetic waves from the very edge of the universe.

Hundreds of thousands of antennas around the world are combined into one radio telescope Square Kilometerre Array

Such radio telescopes are deployed throughout ground Shar., And many of them are planned to be combined into a single Square Kilometer Array (SKA) system, which has a total reception area of \u200b\u200bmore than one square kilometer, as you probably guessed out of the name. It will include more than two thousand antenna systems located in Africa and half a million complexes from Western Australia. The SKA project participates 10 countries: Australia, Canada, China, India, Italy, Netherlands, New Zealand, South Africa, Sweden and United Kingdom:

No one has ever built anything like that. The SKA radio telescope system will solve the most pressing riddles of the universe. He will be able to measure great amount Pulsarov, star fragments and other cosmic telemitting electromagnetic waves along their magnetic poles. Watching such objects near black holes, new will be able to be opened physical laws And, perhaps, a single theory of quantum mechanics and gravity will be developed.

Construction of a unified SKA system begins in stages with smaller component parts And Pathfinder in Australia will be one of these parts. In addition, the SKA1 system is already being built, which will be only a small part of the future Square Kilometer Array, but upon completion of construction will be the largest radio telescope in the world.

SKA1 will include two parts on different continents in Africa and Australia

SKA1 will consist of two parts: SKA1-MID in southern Africa, and Ska1-Low in Australia. SKA1-MID is shown in the figure below and will include 197 mirror antennas with a diameter of 13.5 to 15 meters each:

And the SKA1-LOW system will be calculated for the collection of low-frequency radio waves, which appeared in space billions years ago, when objects like the stars just started their existence. To receive these radio waves, the SKA1-LOW radio telescope will not use mirror antennas. Instead, a set of smaller turnstip antennas, designed to collect signals in a wide range of frequency, including television and FM bands, which coincide with the frequency of radiation of the oldest sources in the universe. SKA1-LOW antennas operate ranging from 50 to 350 MHz, their appearance Showed below:

By 2024, the SKA project executives plan to establish more than 131,000 similar antennas grouped into clusters and the desert scattered in tens of kilometers. In one cluster, 256 such antennas will be included, the signals of which will be combined and transmitted through one fiber optic communication line. Low-frequency antennas will work together, taking radiation that emerged in the Universe of billions years ago. And thereby, they will help to understand the physical processes occurring in the distant past.

The principle of operation of radio telescope

Antennas, combined into one common array, work on the same principle as the optical telescope, that's just a radio telescope focuses not optical radiation, but the received radio waves. The laws of physics dictate such requirements that the higher the wavelength received, the greater the diameter of the mirror antenna should be. So, for example, it looks like a radio telescope without the spatial separation of receiving antenna systems, which is a valid five hundred spherical Fast radio telescope in the south-western Guizhou province in China. This radio telescope will also be part of the Square Kilometer Array project (SKA) project:

But it will not be possible to increase the diameter of the mirror to infinity, and the implementation of the interferometer as in the photo above, not always and not everywhere is possible, so you have to use a large number of territorially separated smaller antennas. For example, such a kind of radio astronomy antennas are MURCHISON WIDEFIELD ARRAY (MWA). MWA antennas operate ranging from 80 to 300 MHz:

MWA antennas are also part of the SKA1-LOW system in Australia. They are also able to look into the dark period of the early universe, called the reonion era. This era existed 13 billion years ago (about a billion years after a large explosion), when only the emerging stars and other objects began to heat the universe filled with hydrogen atoms. It is noteworthy that so far can be detected by radio waves emitted by these neutral hydrogen atoms. The waves were emitted with a wavelength of 21 cm, but by the time they reached the earth, there were billions of years of space expansion, stretching them for a few more meters.

MWA antennas will be used to detect an echo of a long past. Astronomers hopes that the study of this electromagnetic radiation will help to understand deeper how the early universe was formed, and as structures similar to the galaxies were formed and changed into this era. Astronomers note that this is one of the main phases during the evolution of the universe, which is absolutely unknown to us.

In the image below section with MWA antennas. Each section contents of 16 antennas, which are combined between themselves into a single network using fiberboard:

MWA antennas take radio waves with parts from different directions at the same time. Incoming signals are enhanced in the center of each antenna using a pair of low-noise amplifiers, and then sent to the nearest beam shaper. There, waveguides of different lengths give the antenna signals a certain delay. With the right choice of this delay, the shaders of the beam "tip" the array pattern of the array so that radio waves coming from a certain section of the sky reach an antenna at the same time as if they were taken by one large antenna.

MWA antennas are divided into groups. Signals from each group are sent to one receiver, which distributes signals between different frequency channels, and then sends them to the central building of the Observatory on fiber. There, with the help of specialized software packages and graph processing blocks, these data is correlated, multiplying the signals from each receiver and integrating them in time. This approach allows you to create a single strong signal, as if it was accepted by one big radio telescope.

Like an optical telescope, the visibility range of such a virtual radio telescope is proportional to its physical size. In particular, for a virtual telescope consisting of a set of mirror or fixed antennas, the maximum resolution of the telescope is determined by its distance between several receiving parts. The larger the distance, the more accurate permission.

Today, astronomers use this property to create virtual telescopes that cover entire continents, which makes it possible to increase the solving the telescope so good to see the black holes in the center of the Milky Way. But the size of the radio telescope is not the only requirement for detailed information about the distant object. The quality of the resolution also depends on the total number of receiving antennas, the frequency band and the arrangement of the antennas relative to each other.

The data obtained using MWA is sent hundreds of kilometers to the nearest data center with a supercomputer. MWA can send more than 25 terabytes of data per day and in the coming years with the Ska1-Low yield will be even higher. And 131,000 antennas in the SKA1-LOW radio telescope, working in one common array, will collect every day of more terabyte data.

But this is how the problem with the power supply of radio telescopes is solved. In the Merchason radio astronomy observatory, the power supply of the antenna complexes is due to the solar panels with a capacity of 1.6 megawatts:

Until recently, the observatory antenna worked on diesel generators, and now, in addition to solar panels, it also has a huge number of lithium-ion batteries that can store 2.6 megawatt-hours. Some parts of the antenna array will soon receive their own solar panels.

In such ambitious projects, the issue of financing is always quite acute. On the this moment The construction budget SKA1 in South Africa and Australia is about 675 million euros. This is the amount set by 10 project member countries: Australia, Canada, China, India, Italy, the Netherlands, New Zealand, South Africa, Sweden and the United Kingdom. But this financing does not cover the entire cost of SKA1, which are hoped by astronomers. Therefore, the observatory is trying to attract more countries To partnership that could increase financing.

Conclusion

Radi-telescopes make it possible to observe distant space objects: pulsars, quasars, etc. This is how, for example, with the help of the FAST radio telescope, I managed to detect a radioulsar in 2016:

After the pulsar is detected, it was possible to establish that the pulsar is a thousand times heavier than the Sun and on Earth one cubic centimeter of such a substance would weigh several million tons. It is difficult to overestimate the importance of information that can be obtained using such unusual radio telescope.

Plan:

Introduction

• 1 device
• 2 Principle of work
  • 2.1 Radio interferometers
• 3 First radio telescopes
  • 3.1 Beginning - Karl Yansky
  • 3.2 Second birth - ribs
• 4 Classification of radio telescope
  • 4.1 Antennas with filled aperture
    • 4.1.1 Paraboloids of rotation
    • 4.1.2 Parabolic cylinders
    • 4.1.3 Antennas with flat reflectors
    • 4.1.4 Earthheads
    • 4.1.5 Antenna lattices (syphase antennas)
  • 4.2 Antennas with unfilled aperture
• 5 List of radio telescope
Notes

Introduction

RTF-32 radio telescope Observatory "Zelenchukskaya", IPA RAS. Located in the North Caucasus.

Radio telescope - Astronomical tool for receiving own radio emission of celestial objects (in the solar system, galaxy and metagalaxy) and the study of their characteristics: coordinates, spatial structure, radiation intensity, spectrum and polarization.

The radio telescope occupies the initial, according to the frequency range, the position among astronomical instruments of the exploration electromagnetic radiation- more high-frequency telescopes of thermal, visible, ultraviolet, x-ray and gamma radiation are higher.

Radi-telescopes preferably position far from the main settlements in order to maximize the electromagnetic interference from broadcast radio stations, television, radars, and other radiating devices. The placement of the radio operator in the valley or lowline even better protects it from the influence of man-made electromagnetic noises.

1. Device

The radio telescope consists of two main elements: an antenna device and a very sensitive receiving device - a radiometer. The radiometer enhances the received antenna radio emission and converts it into a form convenient for registration and further processing.

The designs of the antennas of radio telescope are distinguished by a large variety, which is due to a very wide range of wavelengths used in radio astronomy (from 0.1 mm to 1000 m). The antennas of radio telescope taking MM, CM, DM and meter waves are most often parabolic reflectors like mirrors of conventional optical reflectors. In the focus of the paraboloid, the irradiator is installed - a device collecting radio emission, which is sent to it with a mirror. The irradiator transmits the accepted energy to the input of the radiometer, and, after amplification and detection, the signal is recorded on the tape of the self-sample electrical meter. On modern radio telescopes, an analog signal from the radiometer exit is converted into digital and written to a hard disk in the form of one or more files.

To direct the antennas to the studied area of \u200b\u200bthe sky, they are usually set on azimuth mounts that provide turns in azimuth and height (full-turn antennas). There are also antennas that allow only limited turns, and even completely fixed. The direction of acceptance in the antennas of the last type (usually very large) is achieved by moving the irradiators that perceive the radio emission reflected from the antenna.

2. Principle of work

The principle of the radio telescope is more similar to the principle of the photometer, rather than an optical telescope. The radio telescope cannot build an image directly, it only measures the energy of radiation coming from the direction in which the telescope looks at the telescope. Thus, in order to obtain an image of an extended source, the radio telescope should measure its brightness at each point.

Due to the diffraction of radio waves on the telescope aperture, the direction measurement on the point source occurs with a certain error, which is determined by the antenna pattern and imposes a fundamental restriction on the resolution of the tool:

where λ is the wavelength, D. - diameter of aperture. High resolution allows you to observe smaller spatial details of the objects under study. To improve the resolution, you need to either reduce the wavelength, or increase the aperture. However, the use of low wavelengths increases the quality requirements of the mirror surface (see the Relay Criterion). Therefore, usually go along the way to increase the aperture. An increase in aperture also allows you to improve another important characteristic - sensitivity. The radio telescope must have a high sensitivity to ensure reliable registration as weaker sources as possible. Sensitivity is determined by the level of fluctuations of the density of the flow Δ P. :

where P. - power of own noise of radio telescope, S. - Effective area (collecting surface) antennas, Δ f. - frequency band and t. - Signal accumulation time. To increase the sensitivity of radio telescope, they increase their collecting surface and use low-noise receivers and amplifiers based on maters, parametric amplifiers, etc.

2.1. Radio interferometers

In addition to increasing the diameter of the aperture, there is another way to increase the resolution (or narrow the radiation diagram). If you take two antennas located at a distance d. (base) from each other, the signal from the source to one of them will come a little earlier than before the other. If then signals from two antennas to interfer, then from the resulting signal using a special mathematical reduction procedure can be restored information about the source with effective resolution λ / d. . Such a reduction procedure is called aperture synthesis. Interference can be carried out as hardware, by means of signaling the signal over cables and waveguides into a common mixer and on a computer with a previously digitized by the exact time and stored signals stored on the carrier. Modern technical means allowed to create a RSDB system, which includes telescopes located on different continents and separated by several thousand kilometers.

3. First radio telescopes

3.1. Beginning - Karl Yansky

The exact copy of the radio telescope Karl Yansky is genuine. National Radio Astronomy Observatory (NRAO), Green Bank, West Virginia, United States

The history of radio telescope takes its beginning with the experiments of Karl Yansky, held in 1931. At that time, Jansky worked as a radio engineer at the BELL TELEPHONE LABS polygon. He was instructed to study the direction of the arrival of thunderstorms. For this, Karl Yansky built a vertically polarized unidirectional antenna of the Bruce web type. The design dimensions were 30.5 m in length and 3.7 m in height. The work was carried out on a wave of 14.6 m (20.5 MHz). The antenna was connected to a sensitive receiver, at the exit of which the recorder stood with a large time constant.

Record the radiation received by Yansky February 24, 1932. Maxima (arrows) are repeated after 20 minutes. - Period of full turnover of antenna.

In December 1932, Jansky had already reported on the first results obtained at its installation. The article reported the detection of "... permanent hissing of unknown origin", which "... It is difficult to distinguish from the hiss caused by the noise of the equipment itself. The direction of the arrival of hissing interference changes gradually during the day, making a full turn in 24 hours. " In the two following works, in October 1933 and October 1935, Karl Yansky gradually comes to the conclusion that the source of its new interference is the central region of our galaxy. Moreover, the greatest response is obtained when the antenna is directed to the center of the Milky Way.

Jansky was aware that progress in radio astronomy would require large-sized antennas with more acute charts that should be easily orientable in various directions. He himself suggested the design of a parabolic antenna with a mirror of 30.5 m in diameter to work on meter waves. However, his proposal did not receive support in the United States, and radio astronomy wing.

3.2. Second birth - ribs

Meridian Radio Telececk Grew Rebers

In 1937, the ribs, Waton's Radio Engineer (USA, Illinois) became interested in the work of the Yansky and designed in the backyard houses of his parents antenna with a parabolic reflector with a diameter of 9.5 m. This antenna had a meridian mount, that is, it was managed only at the corner of the place , and the change in the position of the petal of the diagram on direct ascent was achieved due to the rotation of the Earth. The antenna of the edges was less than the Yansky, but worked on shorter waves, and its radiation diagram was significantly sharper. At the antenna, the rabes raise had a conical shape with a 12 ° width over half of the power, while the yoke antenna beam was a fan-shaped form of a width of 30 ° in terms of half-power in the most narrow section.

In the spring of 1939, the ribs discovered 1.87 m (160 MHz) radiation with a noticeable concentration in the plane of the galaxy and published some results.

The radiocard of the sky, obtained by a grown rib in 1944

Improving its equipment, the ribs took the systematic review of the sky and in 1944 published the first radiocards of the sky. On the maps, the central regions of the Milky Way and bright radio sources in the constellation are clearly visible in the constellation, Swan A, Cassiopeia A, Big PSA and Cord. Edges' cards are quite good even compared to modern cards.

After World War II, substantial technological improvements in the field of radio astronomy scientists in Europe, Australia and the United States were made. Thus, the flourishing of radio astronomy began.

4. Classification of radio telescope

A wide range of wavelengths, a variety of research objects in radio astronomy, the rapid pace of radiophysics and radio equipment, a large number of independent radio astronomer teams led to a wide variety of radio telescope types. The most natural to classify radio telescopes in the nature of filling their aperture and according to the methods of microwave fields (reflectors, refractors, independent field entry):

4.1. Antennas with filled aperture

The antennas of this type are similar to the mirrors of optical telescopes and is the most simple and familiar to use. Antennas with filled aperture simply collect a signal from the observed object and focus it on the receiver. The recorded signal also carries scientific information and does not need synthesis. The disadvantage of such antennas is low resolution. Antennas with unfilled aperture can be divided into several classes in the form of their surface and the mount method.

4.1.1. Paraboloids of rotation

Almost all the antennas of this type are mounted on alt-azimuthal mothings and are full-turn. Their main advantages are that such radio telescopes can, as well as optical, to induce the object and lead it. Thus, observations can be carried out at any time as long as the object under study is above the horizon. Typical representatives: Green-Bank radio telescope, RT-70, Kalyazin radio telescope.

4.1.2. Parabolic cylinders

The construction of full-time antennas is associated with certain difficulties associated with a huge mass of such structures. Therefore, build fixed and semi-motivable systems. The cost and complexity of such telescopes is growing much slower with their growing size. The parabolic cylinder collects rays not at the point, but on a straight line parallel to its forming (focal line). Because of this, the telescopes of this type have an asymmetric diagram of the orientation and various resolution on different axes. Another disadvantage of such telescopes is that only part of the sky is available in view of the limited mobility for observation. Representatives: Radiothers Illinois University, Indian Telescope in the UTI.

The course of the rays in the NASE telescope

4.1.3. Antennas with flat reflectors

To work on a parabolic cylinder, it is required that several detectors are placed on the focal line, the signal from which it takes into account the phases. On short waves it is not easy because of the large losses in the communication lines. Flat reflector antennas allow only one receiver to do. Such antennas consist of two parts: a movable flat mirror and a fixed paraboloid. The movable mirror "is guided" to the object and reflects the rays on the paraboloid. A paraboloid concentrates the rays at the focus point where the receiver is located. This telescope is only available part of the sky for observations. Representatives: Kraus radio telescope, a large radio telescope in NASE.

4.1.4. Earthy bowls

The desire to reduce the cost of led astronomers to the thoughts on the use of natural relief as a telescope mirror. The representative of this type was the 300-meter radio telescope Arecibo. It is located in the karst funnel, the bottom of which is paved by aluminum sheets in the form of spheroid. A receiver on special supports is suspended above the mirror. The disadvantage of this tool is that he is available to the sky area within 20 ° from the zenith.

4.1.5. Antenna lattices (syphase antennas)

Such a telescope consists of a plurality of elementary irradiators (dipoles or spirals) located at a distance of less than the wavelength. Thanks to the accurate phase control of each element, it is possible to achieve a high resolution and effective area. The disadvantage of such antennas is that they are manufactured under a strictly defined wavelength. Representatives: BSA radio telescope in Pushchino.

4.2. Antennas with unfilled aperture

The most important for the purposes of astronomy are two characteristics of radio telescope: resolution and sensitivity. In this case, the sensitivity is proportional to the area of \u200b\u200bthe antenna, and the resolution is the maximum size. Thus, the most common round antennas give worst permission with the same efficient area. Therefore, telescopes with small appeared in radio astronomy

DKR-1000 telescope, with unfilled aperture

square, but large resolution. Such antennas were named antennas with unfilled apertureSince they have "holes" in aperture, superior to the wavelength. To obtain an image from such antennas, observations need to be carried out in the synthesis of apertures. For aperture synthesis, two synchronously working antennas located at some distance called base. To restore the source image, you need to measure the signal at all possible bases with some step up to the maximum.

If the antennas are only two, you will have to monitor, then change the database, to monitor the next point, change the database again, etc. Such synthesis is called consistent. This principle works a classic radio interferometer. The disadvantage of serial synthesis is that it requires a lot of time and cannot identify the variability of radio sources at short times. Therefore, it is more often used parallel synthesis. It takes directly a lot of antennas (receivers), which simultaneously perform measurements for all necessary bases. Representatives: "Northern Cross" in Italy, DKR-1000 radio telescope in Pushchino.

Large arrays of the VLA type are often referred to as a sequential synthesis. However, due to the large number of antennas, almost all bases are already presented, and additional permutations are usually not required.

5. List of radio telescope

Notes

1. Big Soviet Encyclopedia - Slovari.yandex.ru/dict/BSE/article/00064/63300.htm?text\u003dradiotellescope&NCID\u003dBSE&stpar3\u003d1.1. - USSR: Soviet Encyclopedia, 1978.
2. Electromagnetic radiation
3. Radi-telescope // Cosmos Physics: Little Encyclopedia - www.astronet.ru/db/fk86/ / ed. R. A. Syunayeva. - 2nd ed. - m.: Owls. Encyclopedia, 1986. - P. 560. - 783 p. - ISBN 524 (03)
4. P.I. Bakulin, E.V. Kononovich, V.I. Morozoz The course of general astronomy. - M.: Science, 1970.
5. 1 2 3 John D. Kraus. Radio astronomy. - m .: Soviet radio, 1973.
6. Jansky K.G. Directional Studies of Atmospherics at Hight Frequencies. - Proc. Ire, 1932. - T. 20. - P. 1920-1932.
7. Jansky K.G. Electrical Disturbances Apparently of Extraterrestrial Origin .. - Proc. Ire, 1933. - T. 21. - P. 1387-1398.
8. Jansky K.G. A Note On The Source of Interstellar Interference .. - Proc. Ire, 1935. - T. 23. - P. 1158-1163.
9. Reber G. Cosmic Static. - Astrophys. J., June, 1940. - T. 91. - P. 621-624.
10. Reber G. Cosmic Static. - Proc. Ire, FEBruary, 1940. - T. 28. - P. 68-70.
11. 1 2 Reber G. Cosmic Static. - Astrophys. J., NovEmber, 1944. - T. 100. - P. 279-287.
12. Reber G. Cosmic Static. - Proc. Ire, August, 1942. - T. 30. - P. 367-378.
13. Kip Thorn. Black holes and time folds. - M.: Publisher physico-mathematical literature, 2007. - P. 323-325. - 616 p. - ISBN 9785-94052-144-4
14. 1 2 3 N.A.Sepkin, D.V. Korolkov, Yu.N.Pariysky. Radio telescopes and radiometers. - m.: Science, 1973.
15. Radiothers Illinois University. - www.ece.illinois.edu/about/history/reminiscence/400ft.html.
16. Telescope in Uty - rac.ncra.tifr.res.in/ort.html
17. , Green-Bank radio telescope, Very Large Array (radio telescope), Siberian solar radio telescope.