The principle of operation and structure of an optical and radio telescope, methods. Radio astronomy. Radio telescopes. Main characteristics
The photo shows the Murchison Radio Astronomy Observatory, which is located in Western Australia. It includes 36 complexes with such mirror antennas operating in the 1.4 GHz range. The diameter of the main mirror of each antenna is 12 meters. Together, these antennas form part of one large radio telescope, Pathfinder. This is the largest radio telescope in existence today.
Dozens of reflective antennas are used for research and observation of the galaxy. They are able to look into such distances that the world's largest optical telescope, Hubble, is not capable of. 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, the Square Kilometer Array.
Similar radio telescopes are deployed throughout to the globe, and many of them are planned to be combined into a single Square Kilometer Array (SKA) system by 2030, with a total receiving area of more than one square kilometer, as you probably guessed from 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 involves 10 countries: Australia, Canada, China, India, Italy, the Netherlands, New Zealand, South Africa, Sweden and the United Kingdom:
No one has ever built anything like this. The SKA radio telescope system will help solve the most pressing mysteries of the universe. It will be able to measure a huge number of pulsars, stellar fragments and other cosmic bodies that emit electromagnetic waves along their magnetic poles. By observing such objects near black holes, new physical laws can be discovered and, perhaps, a unified theory of quantum mechanics and gravity will be developed.
Construction of a single SKA system begins in stages with smaller components and Pathfinder in Australia will be one of these parts. In addition, the SKA1 system is currently under construction, which will be only a small part of the future Square Kilometer Array, but upon completion it will become 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 reflector antennas with a diameter of 13.5 to 15 meters each:
And the SKA1-low system will be designed to collect low-frequency radio waves that appeared in space billions of years ago, when objects like stars were just beginning to exist. The SKA1-low radio telescope will not use reflective antennas to receive these radio waves. Instead, many smaller turnstile antennas will be installed, designed to collect signals in a wide range of frequencies, including television and FM bands, which coincide with the frequency of the oldest sources in the universe. SKA1-low antennas operate in the range from 50 to 350 MHz, their appearance pictured below:
By 2024, SKA project leaders plan to install more than 131,000 such antennas, grouped in clusters and scattered across the desert for tens of kilometers. One cluster will include 256 such antennas, the signals of which will be combined and transmitted through one fiber-optic communication line. The low-frequency antennas will work together to receive radiation that originated in the universe billions of years ago. And thus, they will help to understand the physical processes occurring in the distant past.
Operating principle of radio telescopes
Antennas combined into one common array work on the same principle as an optical telescope, only the radio telescope focuses not optical radiation, but received radio waves. The laws of physics dictate that the higher the received wavelength, the larger the diameter of the reflector antenna must be. This is, for example, what a radio telescope looks like without spatial diversity of receiving antenna systems - the operating five-hundred-meter spherical radio telescope FAST in the southwestern province of Guizhou in China. This radio telescope will also become part of the Square Kilometer Array (SKA) project in the future:
But it will not be possible to increase the diameter of the mirror indefinitely, and the implementation of an interferometer as in the photo above is not always and not possible everywhere, so you have to use a large number of geographically dispersed antennas of smaller size. For example, this type of antenna for radio astronomy is the Murchison Widefield Array (MWA). MWA antennas operate in the range from 80 to 300 MHz:
MWA antennas are also part of the SKA1-low system in Australia. They are also able to peer into a dark period of the early universe called the era of reionization. This era existed 13 billion years ago (about a billion years after the Big Bang), when nascent stars and other objects began to heat up a universe filled with hydrogen atoms. What's remarkable is that radio waves emitted by these neutral hydrogen atoms can still be detected. The waves were emitted at a wavelength of 21 cm, but by the time they reached Earth, billions of years of cosmic expansion had passed, stretching them out several more meters.
MWA antennas will be used to detect echoes from the distant past. Astronomers hope that studying this electromagnetic radiation will lead to a deeper understanding of how the early universe formed, and how structures like galaxies formed and changed during this era. Astronomers note that this is one of the main phases during the evolution of the Universe, which is completely unknown to us.
The image below shows sections with MWA antennas. Each section contains 16 antennas, which are interconnected into a single network using optical fiber:
MWA antennas receive radio waves in parts from different directions at the same time. Incoming signals are amplified at the center of each antenna by a pair of low-noise amplifiers and then sent to a nearby beamformer. There, waveguides of different lengths impart a certain delay to the antenna signals. At making the right choice With this delay, the beamformers "tilt" the array's radiation pattern so that radio waves coming from a particular area of the sky reach the antenna at the same time, as if they were being received by one large antenna.
MWA antennas are divided into groups. Signals from each group are sent to a single receiver, which distributes the signals between different frequency channels and then sends them to the central observatory building via fiber optics. There, using specialized software packages and graphics processing units, the data is correlated, multiplying the signals from each receiver and integrating them over time. This approach creates a single strong signal, as if it were received by one large radio telescope.
Like an optical telescope, the viewing range of such a virtual radio telescope is proportional to its physical size. In particular, for a virtual telescope consisting of a set of reflective or fixed antennas, the maximum resolution of the telescope is determined by its distance between several receiving parts. The greater this distance, the more accurate the resolution.
Today, astronomers are using this property to create virtual telescopes that span entire continents, allowing them to increase the resolution of the telescope well enough to see the black holes at the center. milky way. But the size of a radio telescope is not the only requirement for obtaining detailed information about a distant object. The quality of resolution also depends on the total number of receiving antennas, the frequency range and the location of the antennas relative to each other.
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 this speed will become even higher in the coming years with the release of SKA1-low. And the 131,000 antennas in the SKA1-low radio telescope, working in one common array, will collect more than a terabyte of data every day.
And this is how the problem with power supply of radio telescopes is solved. At the Murchison Radio Astronomy Observatory, power supply to the antenna complexes is provided by solar panels with a capacity of 1.6 megawatts:
Until recently, the observatory's antennas ran on diesel generators, but now, in addition to solar panels, it also has a huge number of lithium-ion battery packs 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 this moment The construction budget for SKA1 in South Africa and Australia is approximately €675 million. This is the amount set by the project's 10 member countries: Australia, Canada, China, India, Italy, the Netherlands, New Zealand, South Africa, Sweden and the United Kingdom. But this funding does not cover the full cost of SKA1 that astronomers are hoping for. So the observatory is trying to bring more countries into partnerships that could increase funding.
Conclusion
Radio telescopes make it possible to observe distant space objects: pulsars, quasars, etc. This is how, for example, using the FAST radio telescope it was possible to detect a radio pulsar in 2016:
After the discovery of the pulsar, it was possible to establish that the pulsar is a thousand times heavier than the Sun and on earth one cubic centimeter of such matter would weigh several million tons. It is difficult to overestimate the importance of the information that can be obtained using such unusual radio telescopes.
table 2
Telescope characteristics
Perigee - 350,000 km.
Apogee-600km. /2/
The reflective parabolic antenna of the radio telescope has a diameter of 10 meters, consists of 27 petals and a 3-meter solid mirror.
The total mass of the scientific payload is approximately 2600 kg. It includes the mass of the antenna (1500 kg), an electronic complex containing receivers, low-noise amplifiers, frequency synthesizers, control units, signal converters, frequency standards, a highly informative scientific data transmission system - about 900 kg.
IN currently For two-way communication sessions, the largest antenna complexes in Russia, P-2500 (diameter 70 m) in the coastal city of Ussuriysk and TNA-1500 (diameter 64 m) in the village of Medvezhye Ozera near Moscow, are used.
Communication with the Spektr-R device is possible in two modes. The first mode is two-way communication, including the transmission of commands to the board and the reception of telemetric information from it.
The second communication mode is the release of radio interferometric data through a highly directional antenna of a highly informative radio complex (VIRK).
Conclusion
I believe that this work is sufficiently describes the available methods for obtaining cosmic radio emission. Using this work, you can follow trends in the development of radio telescopes. It can be noted that scientists have focused their efforts in improving telescopes more on increasing the angular expansion characteristics than on increasing the sensitivity of radio telescopes. This is most likely due to the fact that increasing sensitivity requires increasing the area, and therefore the diameter, of the antennas (2.5), which is very difficult to do after a certain threshold (150m). Since the observations carried out with the help of 'RadioAstron' turned out to be very productive, I think that radio astronomy will continue to develop in this direction (increasing resolution by increasing the aperture) by placing new orbital observatories that will be similar to 'RadioAstron'. My idea is confirmed by the presence of such a project as SNAP (SuperNova Acceleration Probe), which is planned to be launched in 2020. /5/
List of sources used
1. 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 s.
2. Related definitions[ Electronic resource] // Electronic Encyclopedia: website. - URL: http://ru.wikipedia.org/wiki/(access date: 05/12/2014)
3. Around the world.-M.: Popular Science. 2006-2007
4. Project Radioastron and space radio astronomy [Electronic resource] //Federal Space Agency: website. - URL: http://www.federalspace.ru/185/ (access date: 05/12/2014)
5. Information about the SNAP project [Electronic resource] // Supernova Acceleration Probe:
website. - URL: http://snap.lbl.gov/index.php (access date: 05/12/2014)
Application
Photos of the VLA radio interferomater and photos of the images obtained from them
Rice. 1VeryLargeArray(earthviews)
Rice. 2VeryLargeArray(satellite view) 
Rice. 3Image of the black hole 3C75 in the radio range
We are used to seeing the world in the optical range and hearing in the audio range. Everyone knows that bat sees in the dark thanks to an ultrasonic locator. There are many devices that expand human perception capabilities - this includes all measuring equipment. It displays all sorts of physical processes in graphic or audio form that is accessible to humans.
Technical description
This installation is a two-coordinate scanning device. It operates in the 10 GHz range; TV satellites operate at these frequencies. The original plan was to take a photograph of geostationary orbit. In addition to this, it was interesting to look at the Sun, and also, out of childish curiosity, I wanted to know whether the Moon would be visible and, in general, what would be in the picture.The device uses a parabolic mesh antenna, a converter for the 10-12 GHz range, a two-axis rotary device, with a specially designed control panel, and a program was written to control the rotary device. To digitize the level, a board is assembled from an AD8313 logarithmic level converter, a MAX1236 ADC, and a controller that transmits information to the COM port. The program that controls the rotary device receives data from the ADC, adds time and coordinate marks to it, and saves it to a file. The image is constructed using a simple but necessary algorithm, because The coordinate accuracy is 1 degree, and the data flows at a speed of 10 counts per degree. Because in our case, the plate rotates horizontally, then the horizontal resolution is approximately 10 points per degree, and the vertical resolution is 1 point per degree. A full panoramic shot with a view of 360 degrees in width and 90 degrees in height is taken in about an hour and a half. Thanks to the capabilities of the converter, it is possible to receive radiation with different polarizations separately and obtain different images. Such black and white images can be combined into one color, making the satellites appear multi-colored. Few people realize this, but a parabolic system with a head at the focus of a parabola has the ability to focus not only on satellites, but also try to focus on, for example, a neighboring house, thanks to which you can get clear pictures in which you can see the frame of the greenhouse and even window frames, moreover that the diameter of the parabolic reflector significantly exceeds their width in size.
An example of how a telescope works
Pictures
Focusing
By moving the receiver out of the focus of the parabola, you can focus at different distances.
The top image is focused on the satellites, and the bottom image is focused on the house, with the satellites becoming more blurred.
Aura
At first, when it was necessary to configure the operation of the entire system, the Eutelsat36B satellite in geostationary orbit at 36º east longitude was taken as the reference point. When was received by us positive result, we took a wide shot and saw the trees. They were very blurry and an aura was visible around them at some distance. Later, with adjustments and additional processing in Photoshop and understanding of the projection, it became visible and clear that the aura of the trees is the wires of power lines.
Moon
Everyone knows that not only the Moon, but also a brighter object, the Sun, revolves around the Earth, as you can see by watching this animation, in which both luminaries are visible.
Northern lights
Anyone who has tried to watch satellite television in rain or snow, when there is only one solid dark cloud in the sky, knows that the quality of the received signal depends on the weather conditions. In this case, it is obvious that the radio signal from the satellite is extinguished in the clouds. But there are other factors that affect the quality of reception, for example, radiation from the Sun. We have noticed that often some time after strong solar flares, images from weather satellites are received with very strong noises– it’s the ionosphere that works, creating noise.We took the pictures during a period of sunny stormy weather. Naro-Fominsk. The effect occurred after sunset.
The animation shows the moving Sun.
Flashes on the ground
Once, during periodic photography, long-lasting powerful flashes were noticed, occupying most of the sky. It's hard to get a real snapshot if one shot is taken over 8 minutes, but you can look at the animation done as it was possible.
If you have anything to say about outbreaks or simply have something to add to this topic, please write in the comments.
All images can be viewed here.
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A radio telescope is a type of telescope and is used to study the electromagnetic radiation of objects. It allows you to study electromagnetic radiation astronomical objects in the range of carrier frequencies from tens of MHz to tens of GHz. Using a radio telescope, scientists can receive an object's own radio emission and, based on the data obtained, study its characteristics, such as the coordinates of sources, spatial structure, radiation intensity, as well as spectrum and polarization.
Radiocosmic radiation was first discovered in 1931 by Karl Jansky, an American radio engineer. While studying atmospheric radio interference, Jansky discovered constant radio noise. At that time, the scientist could not exactly explain its origin and identified its source with Milky Way, namely with its central part, where the center of the galaxy is located. Only in the early 1940s, Jansky’s work was continued and contributed to further development radio astronomy.
A radio telescope consists of an antenna system, a radiometer and recording equipment. A radiometer is a receiving device that measures low-intensity radiation power in the radio wave range (wavelengths from 0.1 mm to 1000 m). In other words, the radio telescope occupies the lowest frequency position compared to other instruments with which electromagnetic radiation is studied (for example, an infrared telescope, an X-ray telescope, etc.).
An antenna is a device for collecting radio emissions from celestial objects. The essential characteristics of any antenna are: sensitivity (that is, the minimum possible signal for detection), as well as angular resolution (that is, the ability to separate emissions from several radio sources that are located close to each other).
It is very important that the radio telescope has high sensitivity and good resolution, since this is what makes it possible to observe smaller spatial details of the objects under study. The minimum flux density DP that is recorded is determined by the relation:
DP=P/(S\sqrt(Dft))
where P is the power of the radio telescope's own noise, S is the effective area of the antenna, Df is the frequency band that is received, t is the signal accumulation time.
Antennas used in radio telescopes can be divided into several main types (classification is made depending on the wavelength range and purpose):
Full Aperture Antennas: parabolic antennas (used for observation at short waves; mounted on rotating devices), radio telescope with spherical mirrors (wave range up to 3 cm, fixed antenna; movement in space of the antenna beam is carried out by irradiation different parts mirrors), Kraus radio telescope (wavelength 10 cm; a fixed vertically located spherical mirror, to which the radiation of the source is directed using a flat mirror installed at a certain angle), periscopic antennas (small in size vertically and large in the horizontal direction);
Blank Aperture Antennas(two types depending on the image reproduction method: sequential synthesis, aperture synthesis - see below). The simplest instrument of this type is a simple radio interferometer (interconnected systems of two radio telescopes for simultaneous observation of a radio source: it has greater resolution, example: Aperture fusion interferometer in Cambridge, England, wavelength 21 cm). Other antenna types: cross (successive fusion Mills cross at Molongo, Australia, wavelength 73.5 cm), ring (successive fusion type instrument at Kalgur, Australia, wavelength 375 cm), compound interferometer (aperture fusion interferometer at Flers , Australia, wavelength 21).
The most accurate in operation are full-rotation parabolic antennas. If they are used, the sensitivity of the telescope is enhanced due to the fact that such an antenna can be directed to any point in the sky, accumulating a signal from a radio source. Such a telescope isolates signals from cosmic sources against a background of various noises. The mirror reflects radio waves, which are focused and captured by the irradiator. The irradiator is a half-wave dipole that receives radiation of a given wavelength. The main problem with using radio telescopes with parabolic mirrors is that when rotated, the mirror is deformed under the influence of gravity. It is because of this that when the diameter increases beyond approximately 150 m, the deviations in measurements increase. However, there are very large radio telescopes that have been operating successfully for many years.
Sometimes, for more successful observations, several radio telescopes are used, installed at a certain distance from each other. Such a system is called a radio interferometer (see above). The principle of its operation is to measure and record the oscillations of the electromagnetic field that are generated by individual rays on the surface of a mirror or other point through which the same ray passes. After this, the records are added taking into account the phase shift.
If the array of antennas is made not continuous, but spaced over a sufficiently large distance, then a large-diameter mirror will be obtained. 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 by their diameter. Thus, this system allows you not to build huge antennas, but to get by with 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, the state of New Mexico. The "Very Large Grille" was created in 1981. The system consists of 27 fully rotating 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 72 positions while moving along the rail tracks. The sensitivity of VLA corresponds to an antenna with a diameter of 136 kilometers and the angular resolution exceeds the best optical systems. It is no coincidence that the VLA was used in the search for water on Mercury, radio coronas around stars and other phenomena.
By design, radio telescopes are most often open. Although in some cases, in order to protect the mirror from weather conditions (temperature changes and wind loads), the telescope is placed inside a dome: a solid one (Highstack Observatory, 37-m radio telescope) or with a sliding window (11-m radio telescope at Kitt Peak, USA).
Currently, the prospects for using radio telescopes are that they make it possible to establish communication between antennas located in different countries and even on different continents. Such systems are called very long baseline radio interferometers (VLBI). A network of 18 telescopes was used in 2004 to observe the Huygens lander on Saturn's moon Titan. The ALMA system, consisting of 64 antennas, is being designed. The prospect for the future is the launch of interferometer antennas into space.
I continue the story about the New Year’s trip to the “land of telescopes” that I started (the largest optical telescope in Eurasia with a diameter of the main monolithic mirror of 6 m). This time we will talk about two of its relatives - the RATAN-600 and RTF-32 radio telescopes. The first is listed in the Guinness Book of Records, and the second is part of the only radio interferometric complex “Kvazar” constantly operating in Russia. By the way, now the Kvazar complex is playing important role in the operation of the GLONASS system. Let's talk about everything in more detail and as accessible as possible!
Now let's have some fun! :)
For science, the main advantages of the telescope are multi-frequency (range from 0.6 to 35 GHz) and a large aberration-free field (which allows almost instantaneous measurement of radio spectra of cosmic sources in a wide frequency range), high resolution and high sensitivity by brightness temperature (which allow studies of extended structures, such as fluctuations of microwave background radiation on small angular scales, unattainable even with specialized spacecraft and ground-based instruments).
The telescope consists of two main reflectors:
1. Circular reflector (on the right and along the entire image).
This is the largest part of the radio telescope, it consists of 895 rectangular reflecting elements measuring 11.4 by 2 meters, located in a circle with a diameter of 576 meters. They can move in three degrees of freedom. The circular reflector is divided into 4 independent sectors, named after the parts of the world: north, south, west, east. The total area is 12,000 m². The reflective elements of each sector are aligned in a parabola, forming a reflective and focusing strip of the antenna. A special feed is located at the focus of such a strip.
2. Flat reflector (left).
The flat reflector consists of 124 flat elements with a height of 8.5 meters and a total length of 400 meters. The elements can rotate about a horizontal axis located near ground level. To carry out some measurements, the reflector can be removed by aligning its surface with the plane of the ground. The reflector is used as a periscopic mirror. During operation, the flux of radio emission hitting the flat reflector is directed towards the southern sector of the circular reflector. Having reflected from a circular reflector, the radio wave is focused on the irradiator, which is installed on ring rails. By installing the irradiator in a given position and rearranging the mirror, you can direct the radio telescope at given point sky. A source tracking mode is also possible, in which the irradiator continuously moves, and the mirror is also rearranged.
12. View of a flat reflector with reverse side. The mechanisms that set the plates in motion are visible.
13. The radio telescope has five receiving irradiator cabins installed on railway platforms with radio receiving equipment and observers. Some resemble an armored train, others alien ships. In the photo we see two such cabins. As planned, the platforms can move along one of 12 radial paths, which provides a set of fixed azimuths in 30° increments. The relocation of the irradiators between the tracks should have been carried out using the central turntable (in the center of the photo)... This was intended, but then this was abandoned (and that’s enough) and the turntable is not used, and part of the rails have been dismantled.
14. At the end of 1985, an additional conical reflector-irradiator was installed. The basis is a conical secondary mirror, under which the irradiator is located. It allows you to receive radiation from the entire circular reflector, while achieving the maximum resolution of the radio telescope. However, in this mode, only radio sources can be observed whose direction deviates from the zenith by no more than ±5 degrees. This irradiator most often appears in illustrations related to the telescope, probably because of its alien appearance :)
15. It’s also good to remove the general radio telescope from the top platform of this irradiator. Well, in general, I’m glad that there is an opportunity to climb :) There was no such opportunity on the RTF-32.
By the way, there was a curiosity that led to the formation of a persistent local “urban legend”. When the first observations were made at RATAN, in order to avoid interference from vehicles, traffic along the village of Zelenchukskaya near RATAN was stopped. The closed nature of the telescope and the lack of sufficient information about this structure, close to the village and impressive in its size, gave rise to various myths among the local population - that RATAN allegedly “irradiates”. Perhaps this rumor was also facilitated by the name “irradiators” - although in fact they emit absolutely nothing, but only receive a signal.
16. Cabin No. 1 is in position, observations will begin in a few minutes, but for now we are invited to go inside this “armored train.”
14. Our guide and workplace observer.
What tasks are set for RATAN?
- detection large number cosmic sources of radio emission, identifying them with space objects;
- study of radio emission from stars;
- study of quasars and radio galaxies;
- study of solar system bodies;
- studies of areas of increased radio emission on the Sun, their structure, magnetic fields;
- detection of artificial signals of extraterrestrial origin (SETI);
- research of cosmic microwave background radiation.
The telescope explores astronomical objects over the entire range of distances in the Universe: from the closest ones - the Sun, solar wind, planets and their satellites in the solar system, to the most distant star systems - radio galaxies, quasars and the cosmic microwave background. Over 20 scientific programs of both domestic and foreign applicants are being carried out at the radio telescope.
According to the project "Genetic Code of the Universe" on RATAN-600 all components of background radiation are studied at all angular scales. Daily observations of the Sun with a radio telescope provide unique information, complemented by other instruments, about the properties of solar plasma in the altitude range from the chromosphere to the lower corona, that is, those regions of the Sun’s atmosphere where powerful solar flares originate. This information makes it possible to predict outbreaks of solar activity that affect the well-being of people and the operation of energy systems on the planet. Currently, the RATAN-600 observational data archive contains more than half a million records of radio objects.
15. And this is what radiometers, measuring and recording equipment look like. Some have remained from the time of the first observations, and some have already been replaced with modern equipment. One thing can be said - the radio telescope lives and develops, also being an experimental platform for engineers.
16. This concludes our excursion to RATAN-600: the radio telescope is loaded with observations and it is impossible to distract the people working there.
So, RATAN-600 is still the world's largest reflector mirror and the main radio telescope in Russia, operating in the central "transparency window" of the earth's atmosphere in the wavelength range 1-50 cm. No other radio telescope in the world has such frequency overlap with the possibility carrying out simultaneous observations at all frequencies. Thanks to him and the nearby BTA, astronomers around the world know the names of the villages of the Zelenchuk and Karachay-Cherkess Republics.
17. I took a photo at the top of the “UFO”, as a souvenir :)
P.S. I hope I didn't bore you too much with technical details?