The principle of action of radio telescope. Antennas not for communication: the world's largest radio telescope

Modern radio telescopes allow you to explore the universe in such details that have recently been outside the possible possible not only in the radio view, but also in the traditional astronomy of visible light. United network tools located on different continents allow you to look into the very core of the radioigalaxy, quasars, young stellar clusters that are formed by planetary systems. Radio interferometers with super-long bases thousands of times surpassed the largest optical telescopes. With their help, you can not only track moving spacecraft In the vicinity of distant planets, but also explore the movements of the crust of our own planet, including directly "feel" drift of the mainland. The queue of space radio interferometers, which will allow even deeper to penetrate the secrets of the universe.

The earth's atmosphere is transparent not for all types of electromagnetic radiation coming from space. It has only two wide "transparency windows". The center of one of them falls on the optical area in which the maximum of the radiation of the Sun is lies. It was to him as a result of evolution adapted by human eye sensitivity, which perceives light waves with a length of 350 to 700 nanometers. (In fact, this is a transparency window even a little wider - about 300 to 1,000 nm, that is, captures the near ultraviolet and infrared bands). However, the rainbow strip of visible light is only a small share of the richness of the "colors" of the Universe. In the second half of the 20th century, astronomy became truly Vsevolovna. Achievements of technology allowed astronomers to observe in new ranges of the spectrum. With a short-wave side from visible light, ultraviolet, x-ray and gamma ranges are lying. On the other side there are infrared, submillimeter and radio bands. For each of these ranges, there are astronomical objects that exactly in it are the most relief, although in optical radiation they may not be anything outstanding, so astronomers until recently they simply did not notice them.

One of the most interesting and informative range of spectrum for astronomy is radio waves. Radiation, which registers ground radio astronomy, passes through the second and much more wide window The transparency of the earth's atmosphere - in the wavelength range from 1 mm to 30 m. The ionosphere of the Earth - the layer of ionized gas at an altitude of about 70 km - reflects into space all radiation on the waves is longer than 30 m. On the waves in short, 1 mm cosmic radiation completely "eaten" molecules Atmospheric (mainly oxygen and water vapor).

The main characteristic of the radio telescope is its radiation diagram. It shows the sensitivity of the tool to signals coming from different directions in space. For the "classic" parabolic antenna, the focus chart consists of the main petal having a type of cone oriented on the paraboloid axis, and several much more (for orders) of weaker side lobes. "Troopness" of the radio telescope, that is, its angular resolution, determined the width of the main petal of the radiation pattern. Two sources in the sky, which together fall into a solution of this petal, merge for the radio telescope in one. Therefore, the width of the orientation diagram determines the size of the most small details Heavenly radio source, which can still be distinguished separately.

The universal for the telescope is a rule that the resolution of the antenna is determined by the ratio of the wavelength to the diameter of the telescope mirror. Therefore, to increase the "zorka", the telescope should be more, and the wavelength is smaller. But how the radio telescopes are working with the longest waves of the electromagnetic spectrum. Because of this, even huge sizes of mirrors do not allow high resolution. Not the largest modern optical telescope with a 5 m mirror diameter can distinguish the stars at a distance of only 0.02 angular second. The details of about one minute of arc are visible to the naked eye. A radio telescope with a diameter of 20 m on a wave of 2 cm gives permission even three times worse - about 3 angular minutes. The shot of the sky, made by the amateur camera, contains more details than the radio emission map of the same area obtained by a single radio telescope.

A wide electron diagram limits not only telescope's visual sharpness, but also the accuracy of determining the coordinates of the observed objects. Meanwhile, the exact coordinates are needed to compare the observations of the object in different ranges of electromagnetic radiation - this is an indispensable requirement of modern astrophysical studies. Therefore, radio astronomers have always strived for creating as large antennas as possible. And, no matter how surprisingly, radio astronomy eventually overtook the optical resolution.

Single discharge record holders

Four-turn parabolic antennas - analogues of optical reflector telescopes - turned out to be the most flexible in the work of the variety of radio astronomy antennas. They can be sent to any point of the sky, follow the radio source - "save the signal", as radio astronomers say, and thereby increase the sensitivity of the telescope, its ability to allocate in the background of all sorts of noise, much weaker signals of cosmic sources. The first large total-turn paraboloid with a diameter of 76 m was built in 1957 in the British Observatory of Jodrell-Bank. And today a plate of the world's largest mobile antenna in the Green-Bank Observatory (USA) has dimensions of 100 to 110 m. And this is practically the limit for single movable radio telescope. The increase in diameter has three important investigations: two good and one bad. First, the most important for us is proportional to the diameter increases the angular resolution. Secondly, sensitivity grows, and much faster, in proportion to the area of \u200b\u200bthe mirror, that is, the square of the diameter. And, thirdly, the cost is even faster, which in the case of a mirror telescope (both optical and radio) is approximately proportional to the cube of the diameter of its main mirror.

The main difficulties are associated with mirror deformations under the influence of gravity. To the telescope mirror clearly focused radio waves, the surface deviations from the perfect parabolic should not exceed one tenth of the wavelength. Such accuracy is easily achieved for waves a length of several meters or decimeters. But on short centimeter and millimeter waves, the required accuracy is already tenths of a millimeter. Due to the deformations of the design under its own weight and wind loads, it is almost impossible to create a full-time parabolic telescope with a diameter of more than 150 m. The largest fixed plate with a diameter of 305 m is built in the Arecibo observatory, Puerto Rico. But in general, the Epoch of Giantia in the construction of radio telescope approached the end. In Mexico on the Sierra Negra Mount, at an altitude of 4,600 meters, the construction of a 50-meter antenna for work in the range of millimeter waves is completed. Perhaps this is the last large single antenna created in the world.

In order to see the details of the structure of radio sources, you need other approaches in which we have to deal.

Radio waves emitted by the observed object are distributed in space, generating periodic changes in the electrical and magnetic field. A parabolic antenna collects the radio wave fallen on it at one point - focus. When a few passes through one point electromagnetic wavesThey interfer, that is, their fields are folded. If the waves come in the phase - they enhance each other, in antiphase - weaken, up to a complete zero. The pearabolic mirror feature is that all waves from one source come into focus in the same phase and strengthen each other as possible ways! On this idea, the functioning of all mirror telescopes is based.

The focus arises a bright spot, and here the receiver is usually placed here, which measures the total intensity of the radiation caught within the telescope pattern limits. Unlike optical astronomy, the radio telescope cannot take a photo of the sky. At any moment, it fixes radiation coming only from one direction. Roughly speaking, the radio telescope works as a single-scene camera. To build an image, you have to scan the radio source point per point. (However, a millimeter radio telescope under construction in Mexico has a focus matrix of radiometers and "single-pixel" no longer.)

Command game

However, you can go differently. Instead of bringing all the rays into one point, we can measure and record oscillations of the electric field, generated by each of them on the surface of the mirror (or at another point, through which the same beam passes), and then "fold" these records in the computer device Processing, taking into account the phase shift corresponding to the distance that each of the waves remained to go to the imaginary antenna focus. The device acting on this principle is called the interferometer, in our case, the radio interferometer.

Interferometers are eliminated from the need to build huge one-piece antennas. Instead, you can arrange tens, hundreds and even thousands of antennas and combine the signals accepted by them. Such telescopes are called syphase lattices. However, they still do not solve the problem - for this you need to take another step.

As you remember, with an increase in the size of the radio telescope, its sensitivity grows much faster than the resolution. Therefore, we quickly find ourselves in a situation where the power of the recorded signal is more than enough, and the angular permission is not enough. And then the question arises: "Why do we need a solid grating antennas? Is it possible to break it? " It turned out that you can! This idea was called the "Aperture Synthesis", since from several separate independent antennas placed on a large area, "synthesized" a mirror of much larger diameter. The resolution of such a "synthetic" tool is determined not by the diameter of individual antennas, but the distance between them - the base of the radio interferometer. Of course, the antennas must be at least three, and they should not be placed along one straight line. Otherwise, the resolution of the radio interferometer will be extremely inhomogeneous. It will turn out to be high only in the direction along which antennas are separated. In the transverse direction, the resolution will still be determined by the size of individual antennas.

On this path, radio astronomy began to evolve in the 1970s. During this time, a number of large multi-penal interferometers were created. Some of them are stationary antennas, others can move along the surface of the Earth to conduct observations in different "configurations". Such interferometers build "synthesized" radio source maps with a much higher resolution than single radio telescopes: it reaches 1 angular second on centimeter waves, and this is already comparable to the resolution of optical telescopes when observing through the atmosphere of the Earth.

The most famous system of this type is the "very large lattice" (Very Large Array, VLA) - built in 1980 in the US National Radio Astronomy Observatory. Its 27 parabolic antennas each with a diameter of 25 m and weighing 209 tons move along three radial rail tracks and can be removed from the center of the interferometer to a distance of 21 km.

Today there are other systems: Westerbork in Holland (14 antennas with a diameter of 25 m), ATCA in Australia (6 antennas at 22 m), Merlin in the UK. In the last system, along with 6 other tools scattered throughout the country, the famous 76-meter telescope is included. In Russia (in Buryatia), a Siberian solar radio interferometer was created - a special system of antennas for the operational study of the Sun in the radio view.

In 1965, Soviet scientists L.I. Matveenko, N.S. Kardashev, GB Sholomitsky offered independently registering data on each antenna of the interferometer, and then jointly process them, as if simulating the interference phenomenon on the computer. This allows you to cut antennas at arbitrarily long distances. Therefore, the method was called radio interferometry with super long bases (RSDB) and is successfully used since the early 1970s. The record length of the base, achieved in experiments, is 12.2 thousand km, and the permission on the wave of about 3 mm reaches 0.00008 '' - three orders of magnitude higher than that of large optical telescopes. It is hardly possible to significantly improve this result on Earth, since the size of the base is limited to the diameter of our planet.

Currently, systematic observations are conducted by several networks of intercontinental radio interferometers. In the United States, a system has been created, which includes 10 radio telescope on an average diameter of 25 m, located in the continental part of the country, in the Hawaiian and Virgin Islands. In Europe, the 100-meter Bonn telescope and 32-meter in Medicina (Italy), Merlin interferometers, Westerbork, and other tools are regularly united for RSDB experiments. This system is called EVN. There is also a global international network of radio telescope for astrometry and geodesy IVS. And recently in Russia began to operate its own interferometric network "Quasar" of three 32-meter antennas located in the Leningrad region, in the North Caucasus and in Buryatia. It is important to note that telescopes are not fixed hard for RSDB networks. They can be used autonomously or switch between networks.

Interferometry with super-long bases requires a very high measurement accuracy: it is necessary to fix the spatial distribution of highs and minima of electromagnetic fields with an accuracy of the loss of the wavelength, that is, for short waves to the share of centimeter. And S. highest accuracy Note the time in which measurements were carried out on each antenna. Atomic frequency standards are used as ultralone clocks in the experiments of the RSDB.

But do not think that radio interferometers no flaws. In contrast to a solid parabolic antenna, the interferometer orientation diagram instead of one main petal has hundreds and thousands of narrow petals of comparable magnitude. Build a source card with such a diagram of the orientation is the same as to feel the keyboard of the computer by frozen fingers. Image recovery is complex and, moreover, "incorrect" (that is, unstable to small changes in the measurement results) the task that, however, the radio astronomers have learned to decide.

Achievements of radio interferometry

The radio interferometers with an angular resolution in the thousandth fractions of a second arc "looked" in the most internal areas of the most powerful "radio beacons" of the Universe - radio-belaxes and quasars, which radiate in the radio parasone are tens of millions of times more intense than ordinary galaxies. It was possible to "see", as the plasma clouds of galaxies and quasars are thrown out, measure the speed of their movement, which turned out to be close to the speed of light.

Many interesting was open and in our galaxy. In the vicinity of young stars, the sources of maser radio emission were found (a maser is an analogue of an optical laser, but in the radio band) in the spectral lines of water molecules, hydroxyl (OH) and methanol (CH 3 OH). On a space scale, sources are very small - less than the solar system. Separate bright specks on radiocards obtained by interferometers can be embrying planets.

Such maasers are found in other galaxies. Changing the provisions of Maseric spots for several years, observed in the neighboring M33 galaxy in the constellation of the triangle, for the first time, made it possible to directly assess the speed of its rotation and move across the sky. The measured shifts are insignificant, their speed is in many thousands of times less visible for the earth observer of the snail speed that crawls over the surface of Mars. Such an experiment is still far beyond the abilities of optical astronomy: to notice its own movements of individual objects at intergalactic distances, it is simply not under power.

Finally, interferometric observations gave a new confirmation of the existence of supermassive black holes. Around the core of the active galaxy NGC 4258, a bunch of substances were found, which are moving in orbits by a radius of no more than three light years, while their speeds reach thousands of kilometers per second. This means that the mass of the central body of the galaxy is at least a billion mass of the Sun, and it cannot be nothing more than a black hole.

A number of interesting results are obtained by the RSDB method when observed in the solar system. To begin at least with the most accurate quantitative verification of the general theory of relativity. The interferometer measured the deviation of radio waves in the field of the Sun, with an accuracy of the hundredth of percent. It is two orders of magnitude more accurate than optical observations allow.

Global radio interferometers are also used to monitor the movement of spacecraft studying other planets. For the first time, such an experiment was conducted in 1985, when the Soviet devices "Vega-1" and "-2" dropped aerostats into the atmosphere. The observations confirmed the quick circulation of the atmosphere of the planet at a speed of about 70 m / s, that is, one turn around the planet in 6 days. it amazing factwho still expects his explanation.

Last year, similar observations with the network of 18 radio telescope on different continents were accompanied by the landing of the Guygens apparatus on Saturn Titan satellite. From a distance of 1.2 billion km, it was tracking for how the device is moving in the titanium atmosphere with an accuracy of a tent of the kilometers! It is not too widely known that during the landing of Guuygens, almost half of scientific information was lost. The probe retransmitted data through the Cassini station, which delivered it to Saturn. For reliability, two duplicate data transfer channels were envisaged. However, shortly before the landing, it was decided to transmit different information on them. But in the most responsible moment, because of the yet, one of the receivers, one of the receivers on "Cassini" did not turn on, and half the pictures disappeared. And with them there are also data on wind speed in the titanium atmosphere, which were transmitted just on the disconnected channel. Fortunately, Nasa managed to progress - the "Guigens" descent watched the global radio interferometer from the ground. It seems to be allowed to save the missing data on the dynamics of the Titan's atmosphere. The results of this experiment are still treated in the European Unified Radio Interferometric Institute, and, by the way, our compatriots Leonid Gurwitz and Sergey Pogrebainko are engaged in this.

RSDB for land
The method of radio interferometry is also clean practical applications - No wonder, for example, in St. Petersburg, this topic is engaged in the Institute of Applied Astronomy of the Russian Academy of Sciences. Observations on RSDB technology make it possible not only to determine the coordinates of radio sources with an accuracy of the ten thousandth of the second of the arc, but also measure the provisions of the radio telescope themselves on Earth with an accuracy better than one millimeter. This, in turn, makes it possible with the highest accuracy to track the variations of the Earth's rotation and the movement of the earth's crust.

For example, it was using the RSDB that the continent's movement was experimentally confirmed. Today, the registration of such movements has already become a routine business. Interferometric observations of distant radio phosigas are firmly entered into the arsenal of geophysics along with the seismic sensing of the Earth. Due to it, periodic stations shifts are reliably recorded relative to each other caused by the deformations of the earth's crust. Moreover, not only long-term solid-state tides are noted (for the first time registered by the RSDB method), but also a deflection arising under the influence of changes in atmospheric pressure, water weight in the ocean and groundwater weights.

To determine the parameters of the rotation of the Earth in the world, heavenly radio sources are being observed daily, coordinated by the international RSDB service for astrometry and IVS geodesy. The obtained data is used, in particular, to detect the drift of the planes orbits of the GPS positioning system satellites. Without making appropriate amendments received from RSDB observations, the error of determining longitude in the GPS system would be more than now. In a sense, the RSDB plays for GPS navigation the same role as the exact marine chronometers for navigating the stars in the XVIII century. The exact knowledge of the parameters of the earth's rotation is also necessary for the successful navigation of interplanetary space stations.

Leonid Petrov, Center for Space Flights. Goddard, NASA.

Tools of Future

At least in the next half a century, the general line of radio astronomy development will be the creation of increasingly large aperture synthesis systems - all designable large tools are interferometers. So, at the plateau, the chaventer in Chile jointly, the construction of the Alma Millime Range (ATACAMA LARGE MILLIMETER ARRAY is the construction of a large millimeter system ataction) at the co-efforts of a number of countries in Europe and America. In total there will be 64 antennas with a diameter of 12 meters with a working wavelength range from 0.35 to 10 mm. The greatest distance between Alma antennas will be 14 km. Thanks to a very dry climate and high height above sea level (5100 m), the system will be able to observe the waves in shorter of the millimeter. In other places and at a lesser height, it is impossible due to the absorption of such radiation with water in the air. Construction ALMA will be completed by 2011.

The European Aperture Synthesis LOFAR system will work on much longer waves - from 1.2 to 10 m. It will be commissioned for three coming years. This is very interesting project: To reduce the cost, it uses the simplest fixed antennas - pyramids made of metal rods with a height of about 1.5 m with a signal amplifier. But these antennas in the system will be 25 thousand. They will be united into groups that will be scented throughout the territory of Holland along the rays of the "curved five-pointed star" with a diameter of about 350 km. Each antenna will receive signals from all visible sky, but their joint computer processing will allow to allocate those that came from those interested in scientists. At the same time, a purely computational way is formed by a diagram of the interferometer, the width of which on the shortest wave will be 1 second arc. The operation of the system will require a huge amount of computing, but for today's computers, this is a completely saturated task. To solve it last year in the Netherlands, the most powerful supercomputer IBM Blue Gene / L with 12,288 processors was installed in Europe. Moreover, with appropriate signal processing (requiring even large computer power), Lofar will be able to simultaneously watch several and even on many objects!

But the most ambitious project of a close future is SKA (Square Kilometer Array - the system "square kilometer"). The total area of \u200b\u200bits antennas will be about 1 km2, and the value of the tool is estimated at billion dollars. The SKA project is still at an early development phase. The basic discussed design variant - thousands of antennas with a diameter of several meters operating in the range from 3 mm to 5 m. And the half of them is maintained to be installed on a section with a diameter of 5 km, and the rest of the dissemination of significant distances. Chinese scientists offered an alternative scheme - 8 fixed mirrors with a diameter of 500 m each, similar to a telescope in Arecibo. For their placement, suitable dried lakes were also proposed. However, in September, China dropped out of the countries - applicants for the placement of a giant telescope. Now the main struggle will unfold between Australia and South Africa.

The possibilities of increasing the base of ground interferometers are practically exhausted. The future is the launch of an interferometer antenna into space, where there are no restrictions related to the size of our planet. Such an experiment was already conducted. In February 1997, a Japanese Halca satellite was launched, which worked until November 2003 and completed the first stage in the development international project VSOP (VLBI Space Observatory Programme is a program of the Space Observatory of the RSDB). The satellite carried an antenna in the form of an umbrella with a diameter of 8 m and worked on an elliptical near-earth orbit, which provided the base equal to the three diameters of the Earth. An images of many extragalactic radio sources with a resolution of the arc seconds were obtained. The next stage of the experiment on cosmic interferometry, VSOP-2 is planned to begin in 2011-2012. Another tool of this type is created in the framework of the Radiastron project by AstroComic Center Physical Institute them. PN Lebedeva RAS together with scientists from other countries. The Radiastron satellite will have a parabolic mirror with a diameter of 10 m. During startup it will be in the folded state, and after the exit to orbit will unfold. Radiastron will be equipped with receivers for several wavelengths - from 1.2 to 92 cm. Radio telescopes in Pushchino (Russia), Canberre (Australia) and Green Bank (USA) will be used as ground antennas of the cosmic interferometer. The satellite orbit will be very elongated, with an apogee 350 thousand km. With such a base of the interferometer on the shortest wave, it will be possible to obtain images of radio sources and measure their coordinates up to 8 million dollars of a second of an arc. This will give the opportunity to look at the nearest neighborhood of the nuclei of the radio galaxy and black holes, in the depths of the formations of young stars in the galaxy.

Russian scientists develop a more perfect space radio telescope to work in millimeter and submillimeter bands - Millimetron. The mirror of this tool will be cooled with liquid helium to a temperature of 4 Kelvin (-269 ° C) to reduce thermal noise and increase sensitivity. Several options for the work of this interferometer according to the Space-Earth schemes and space-space (between two telescopes on satellites) are considered. The device can be launched to the same elongated orbit, as in the Radiastron project, or to the Lagrange Point of Sun-Earth System, at a distance of 1.5 million km in the Sunior direction from the Earth (this is 4 times further than the moon). In the last embodiment, on a wave of 0.35 mm, the space-ground interferometer will give an angular resolution to 45 billion dollars of a second of the arc - hundreds of thousands of times better than in modern optical instruments!

Mikhail Prokhorov, Doctor of Physical and Mathematical Sciences
Georgy Rudnitsky, Candidate of Physical and Mathematical Sciences

The telescope is a unique optical device designed to observe the celestial bodies. The use of devices allows you to consider a variety of objects, not only those that are located near us, but also those that are over thousands of light years from our planet. So what is a telescope and who invented him?

First inventor

Telescopic devices appeared in the seventeenth century. However, to this day, a debate is being conducted, who invented the Telescope first - Galilee or Lippershey. These disputes are related to the fact that both scientists at one time at one time conducted the development of optical devices.

In 1608, Lippershey developed glasses for nobility to see remote objects near. At that time, military negotiations were conducted. The army quickly assessed the development of development and suggested Lippershey not to fix the copyright for the device, and to finalize it so that he could look at two eyes. The scientist agreed.

The new development of the scientist failed to hold in secret: information about it was published in local prints. Journalists of that time called the device with a visual pipe. It used two lenses that allowed to increase items and objects. From 1609 in Paris, the pipes with a three-time increase were sold. From this year, any information about Lippershea disappears from history, and information about another scientist and its new discoveries appear.

In about the same years, the Italian Galileo was engaged in grinding lenses. In 1609, he presented a new development to society - a three-time telescope. The Galilee telescope had a higher image quality than Lippershey pipes. It was the brainchild that the Italian scientist received the name "Telescope".

In the seventeenth century, telescopes were made by Dutch scientists, but they had low image quality. And only Galileo managed to develop such a lenz grinding technique, which allowed to increase clear objects. He was able to receive a twenty-fold increase that was in those days a real breakthrough in science. Based on this, it is impossible to say who invented the telescope: if according to the official version, it was Galileo who presented the world to the world that he called the telescope, and if you look at the development version optical device To increase objects, the first was Lippershey.

The first observations of the sky

After the first telescope, unique discoveries were made. Galileo applied its development for tracking heavenly Tel. He first saw and drew the lunar crater, stains in the sun, and also considered the star of the Milky Way, the satellites of Jupiter. Galilean's telescope gave the opportunity to see the rings in Saturn. To note, in the world there is still a telescope, working on the same principle as the Galilean device. It is located in the York Observatory. The device has a diameter of 102 centimeters and properly serves as a scientist for tracking celestial tel.

Modern telescopes

Over the course of centuries, scientists have constantly changed telescope devices, developed new models, improved the multiplicity of the increase. As a result, it was possible to create small and large telescopes that have a different purpose.

Small usually used for domestic observations of space objects, as well as to monitor close space bodies. Large devices allow you to consider and take pictures of the celestial bodies located in thousands of light years from the ground.

Types of telescopes

There are several varieties of telescopes:

1. Mirror.
2. Lenzovy.
3. Catadiopritic.

Lenzov believes Galilee refractors. The mirror includes reflex type devices. And what is a cadiatric telescope? This is a unique modern development, which combines a lens and a mirror device.

Lenzovy telescopes

Telescopes in astronomy play an important role: they allow you to see comets, planets, stars and other space objects. One of the first developments were lenza devices.

Each telescope has a lens. This is the main part of any device. She refracted the rays of the light and collects them at the point, called the focus. It is in it a picture of an object. To view the picture, use eyepiece.

Lens is placed in such a way that the eyepiece and focus coincide. In modern models for convenient observation in the telescope apply movable eyepieces. They help customize image sharpness.

All telescopes have aberration - distortion of the object under consideration. Lens telescopes have several distortions: chromatic (red and blue rays are distorted) and spherical aberration.

Mirror models

Mirror telescopes are called reflectors. They establishes a spherical mirror, which collects a light beam and reflects it using a mirror on the eyepiece. For mirror models, chromatic aberration is not characteristic, since the light is not refracted. However, the mirrored devices expressed spherical aberration, which limits the field of view of the telescope.

In graphic telescopes, complex structures are used, mirrors with complex surfaces that differ from spherical.

Despite the complexity of the design, the mirror models are easier to develop than lenza analogs. therefore this species More common. The largest diameter of the mirror telescope is more seventeen meters. In Russia, the largest apparatus has a diameter of six meters. Over the years, he was considered the largest in the world.

Characteristics of telescopes

Many buy optical apparatus for space bodies. When choosing a device, it is important to know not only what a telescope is, but also what characteristics it possesses.

1. Increase. The focal length of the eyepiece and object is the multiplicity of the telescope increase. If the focal length of the lens is two meters, and in the eyepiece - five centimeters, then such a device will have a sustainable magnification. If the eyepiece is replaced, the increase will be different.
2. Resolution. As you know, the light is characterized by refraction and diffraction. Ideally, any image of the star looks like a disk with several concentric rings, called diffraction. Disk dimensions are limited only by the capabilities of the telescope.

Telescopes without eye

And what is a telescope without eyes, for what is used for? As you know, each person has eyes perceive the image in different ways. One eye can see more, and the other is less. So that scientists can consider everything they need to see, telescopes without eyes. These devices transmit the picture to the screens of monitors through which each sees the image exactly what it is, without distortion. For small telescopes, for this purpose, cameras connected to the devices and removing the sky are developed.

SAME modern methods Cosmos vision was the use of CCD cameras. These are special photosensitive chips that collect information from the telescope and transmit it to the computer. The data obtained from them is so clear that it is impossible to imagine what other devices could receive such information. After all, people's eye cannot distinguish all shades with such high definition, as modern cameras do.

To measure distances between stars and other objects, use special devices - spectrographs. They are connected to the telescopes.

A modern astronomical telescope is not one device, but at once a few. The received data from several devices are processed and displayed on monitors as images. And after processing, scientists get images of very high definition. To see the eyes in the telescope the same clear images of the cosmos is impossible.

Radi-telescopes

Astronomers for their scientific developments use huge radio telescopes. Most often they look like huge metal bowls with a parabolic form. The antennas collect the resulting signal and processed the received information in the image. Radio telescopes can take only one wave of signals.

Infrared models

A bright example of an infrared telescope is the Hubblem apparatus, although it can be at the same time optical. In many ways, the design of infrared telescopes is similar to the design of optical mirror models. Thermal rays are reflected in the usual telescopic lens and focus at one point where the device measuring heat is located. The resulting thermal rays are skipped through thermal filters. Only after that takes photographing.

Ultraviolet telescopes

When photographing, the film can be wounded by ultraviolet rays. In some part of the ultraviolet range, it is possible to take images without processing and illuminating. And in some cases it is necessary that the rays of the light passed through a special design - a filter. Their use helps to allocate radiation of certain sections.

There are other types of telescopes, each of which has its own purpose and special characteristics. These are models such as X-ray, gamma telescopes. In its intended purpose, all existing models can be divided into amateur and professional. And this is not the entire classification of devices for tracking celestial bodies.

table 2

Telescope characteristics

Peria-350000 km.

Apogia 600km. / 2 /

The mirror parabolic radio telescope antenna has a diameter of 10 meters, consists of 27 petals and a 3-meter solid mirror.

The total mass of the useful scientific cargo is approximately 2600 kg. It includes an antenna mass (1500kg), an electronic complex containing receivers, low-noise amplifiers, frequency synthesizers, control units, signal converters, frequency standards, highly informative scientific data transmission system - about 900 kg.

At the moment, the largest antenna complexes of P-2500 (diameter 70 m) in the Primorsky city of Ussuriysk and TNA-1500 (diameter of 64 m) are used for the bilateral communication sessions (diameter of 64 m) in the village of Medvezhy Lake near Moscow.

Communication with the "Spectr-P" apparatus is possible in two modes. The first mode is a bilateral connection, which includes the transfer of commands to board and receive telemetry information from it.

The second communication mode is a reset of radio interferometric data through a high-informative radio terminal antenna (Virk).

Conclusion

I believe that this work is sufficiently describing the methods of obtaining cosmic radio emission. With the help of this work, you can trace the trends in the development of radio telescope. It can be noted that scientists focused their efforts in improving telescopes more on increasing the characteristics of the angular expansion than to increase the sensitivity of radio telescope. This is most likely due to the fact that an increase in sensitivity requires an increase in area, consequently, diameter, antennas (2.5), which is very difficult to do after a certain threshold (150m). Since the observations conducted with the Radiastron were very effective, I think that radio astronomy will continue to develop in this direction (increase in permission due to an increase in aperture) by placing new orbital observatory, which will be similar to 'Radio astron'. My thought confirms the presence of such a project as SNAP (Supernova Acceleration Probe), which is planned to be launched in 2020. /five/

List of sources used

1. Kraus D. D. 1.2. Brief history of the first years of radio astronomy // Radio Astronomy / Ed. V.V. Zheleznyakova. - M.: Soviet radio, 1973. - P. 14-21. - 456 p.

2. Related definitions [Electronic resource] // Electronic Encyclopedia: Site.- URL: http://ru.wikipedia.org/wiki/(Data: 05/12/2014)

3. Around the Light.-M.: Sciential-poppie. 2006-2007

4. Project Radio astron and space radio astronomy [Electronic resource] // Federal Space Agency: Sight. - URL: http://www.federalspace.ru/185/ (Date of handling: 05/12/2014)

5. Information about the Snap Project [Electronic resource] // Supernova Acceleration Probe:

site - URL: http://snap.lbl.gov/index.php (Date of handling: 05/12/2014)

application

Photos of the radio interferomatra VLA and photographs from them images

Fig. 1VERYLARGEARRAY (Vysimensha)

Fig. 2VeryLargeArray (satellite view)

Fig. 3 image of a black hole 3C75 in the radio view

The radio telescope is a type of telescope and is used to study the electromagnetic emission of objects. It allows you to study the electromagnetic radiation of astronomical objects in the range of carrier frequencies from tens of MHz to tens of GHz. Using the radio telescope, scientists can take their own object radio emission and, based on the data obtained, to investigate its characteristics, such as: source coordinates, spatial structure, radiation intensity, as well as spectrum and polarization.

For the first time, radioosmic radiation was discovered in 1931 by Karl Yansky, an American radio engineer. Studying atmospheric radio intercoms, Yansky discovered a permanent radosum. At that time, the scientist immediately could not explain his origin and identified his source with the Milky, namely, with its central part, where the center of the Galaxy is. Only in the early 1940s, the JSC operates were continued and contributed to the further development of radio astronomy.

The radio telescope consists of an antenna system, a radiometer and recording equipment. Radiometer is a receiving device with which the power of low intensity radiation is measured in the radio wave range (wavelengths from 0.1 mm to 1000 m). In other words, the radio telescope occupies the lowest position compared to other devices, with the help of which electromagnetic radiation is investigated (for example, an infrared telescope, an X-ray telescope, etc.).

Antenna is a device for collecting radio emission of celestial objects. The sonic characteristics of any antenna are: Sensitivity (that is, the minimum possible signal for detection), as well as an angular resolution (that is, the ability to divide radiation from several radio sources that are close to each other).

It is very important that the radio telescope has high sensitivity and good resolution, since it is precisely this makes it possible to observe smaller spatial details of the objects under study. The minimum flow density of the DR, which is registered is determined by the ratio:
DP \u003d P / (S \\ SQRT (DFT))
where P is the power of its own noise of radio telescope, S is an effective antenna area, DF - frequency band, which are accepted, T is the time of the signal accumulation.

Antennas used in radio telescopes can be divided into several basic types (the classification is performed depending on the wavelength range and destination):
Full aperture antennas: Parabolic antennas (are used to observe short waves; installed on rotary devices), radio telescope with spherical mirrors (wave range up to 3-cm, fixed antenna; movement in the beam space antenna is carried out by irradiation different parts mirrors), a radiosecraft of the craw (wavelength of 10 cm; a fixed vertically located spherical mirror, on which the source radiation is directed using a flat mirror installed at a certain angle), periscopic antennas (small vertical dimensions and large in the horizontal direction);
Antennas with unfilled aperture(Two types Depending on the image playback method: Sequential synthesis, aperture synthesis - see below). The simplest tool of this type is a simple radio interferometer (related systems from two radio telescope for simultaneous monitoring of the radio source: has a greater resolution, an example: an interferometer with aperture synthesis in Cambridge, England, wavelength 21 cm). Other types of antennas: Cross (Mills cross with a consistent synthesis in Molrelo, Australia, wavelength of 73.5 cm), ring (tool of type of sequential synthesis in Calgur, Australia, wavelength 375 cm), composite interferometer (interferometer with aperture synthesis in fler , Australia, wavelength 21).

The most accurate in the work are full-turn parabolic antennas. If they are used, the sensitivity of the telescope is enhanced by the fact that such an antenna can be sent to any point of the sky, accumulating the signal from the radio source. A similar telescope allocates signals of cosmic sources against the background of a variety of noise. The mirror reflects the radio waves, which focus and are tracked by the irradiator. The irradiator is a half-wave dipole, receiving radiation of a given wavelength. The main problem of using radio telescope with parabolic mirrors is that when turning the mirror is deformed under the action of gravity. It is because of this, in the case of an increase in the diameter, more than 150 m increase the deviations during measurements. Nevertheless, there are very large radio telescopes that successfully work for many years.

Sometimes, for more successful observations, several radio telescopes installed at a certain distance from each other are used. Such a system is called a radio interferometer (see above). The principle of its action consists in measuring and writing the oscillations of the electromagnetic field, which are generated by separate rays on the surface of the mirror or another point through which the same beam passes. After that, the record is consistent with the phase shift.

If the antenna grille is made not solid, but spaced on enough large distanceThen it turns out a large diameter mirror. Such a system works on the principle of "aperture synthesis". In this case, the resolution is determined by the distance between the antennas, and not their diameter. In this way, this system Allows you to not build huge antennas, but to do, at least three, located at certain intervals. One of the most famous systems of this kind is VLA (Very Large Array). This array is located in the USA, New Mexico. "A very large lattice" was created in 1981. The system consists of 27 full-time parabolic antennas, which are located along two lines forming the letter "V". The diameter of each antenna reaches 25 meters. Each antenna can occupy one of the 72 positions, moving along the railway tracks. The sensitivity VLA corresponds to an antenna with a diameter of 136 kilometers and over the angular resolution exceeds the best optical systems. It is no coincidence that the VLA was used when looking for water on Mercury, a radio crown around stars and other phenomena.

By its design, radio telescopes are most often open. Although in some cases in order to protect the mirror from weather phenomena (temperature changes and wind loads), the telescope is placed inside the domes: a solid (Heistec Observatory, 37th radio telescope) or with a sliding window (11th radio telescope on kitt peak, USA).

Currently, the prospects for using radio telescope are that they allow you to establish a connection between the antennas in different countries And even on different continents. Such systems are called an over long-domed base radio interferometers (RSDB). The network of 18 telescopes was used in 2004 to observe the landing of the Guigens apparatus for Titan, Saturn Satuttoe. The design of the ALMA system consisting of 64 antennas is underway. The prospect for the future is the launch of an interferometer antenna into space.

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 space bodies Radio waves reach, reaching the Earth: This, in particular, the external layers of the sun and the atmospheres of the planets, the clouds of interstellar gas. Radio radiation is accompanied by 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 galaxic and quasar nuclei, solar flares, and other radio signals of natural objects 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.

RadiTelliescope - Astronomical tool for receiving own radio emission of celestial objects (in Solar system, Galaxy and metagalaxy) and research 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 light, close (short-wave) 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 the earth's 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 began in 1931, when K.Yansky began to study the interference of the radio and discovered that they come from the central part of the 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 radiometer exit is converted into digital and recorded on 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.

§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 They 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 edges are quite good 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, 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

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 - 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, due to the large number of antennas, almost all bases are already presented, and additional permutations are usually not required.

List of radio telescope.

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