|
Arabic
Bengali
Chinese
English
French
German
Hebrew
Hindi
Italian
Japanese
Korean
Malay
Polish
Portuguese
Spanish
Turkish
Ukrainian
Vietnamese|
CHILDREN'S SCIENTIFIC LABORATORY
On the threshold of distant worlds. Children's Science Lab
Directory / Children's Science Lab Until relatively recently, it seemed that radio electronics and astronomy did not and could not have anything in common. However, these days this opinion is hopelessly outdated. Now, at astronomical conferences, along with questions of the study of planets and stars, they report on new electronic devices, discuss not only photographs of the far side of the Moon, but also the electronic equipment that ensured their transmission ... Radio engineers now make up a significant part of the staff of observatories. This is understandable: in the new large telescopes, there are no less electronics than optics. Here are some of the many examples. On fig. Figure 1 shows an automatic electronic polarimeter developed at the Abastumani Astrophysical Observatory of the Academy of Sciences of the Georgian SSR. This device is an electronic computing device of non-discrete action. By measuring certain parameters of a beam of light, he solves several equations, which include these parameters, and calculates the result in 0,01 seconds. The circuit consists of 38 vacuum tubes and 35 diodes. The studies of the Moon and planets carried out at the observatory with the help of the new instrument provide valuable data on the composition and structure of their surfaces.
Electronic instruments and methods used in astronomy are extremely interesting and unique. It is known that the eye reacts only to a very small interval of wavelengths in the range of electromagnetic oscillations - from 4200 to 7000 angstroms, which corresponds to frequencies from 430 to 715 million megahertz. In this range, optical astronomy is interested in measuring light fluxes - photometry; radiation energy distribution over the range - spectrometry; determination of the plane in which the electric vector of oscillations lies, and the corresponding quantitative relationships - polarimetry, as well as a number of other tasks. All of them are solved by electronic methods. Of course, any electronic device must begin with a receiver of radiant energy that responds to it with the appearance of current, voltage, or a change in resistance. These receivers are characterized primarily by the range in which they must operate, and sensitivity. The most common type of receiver used in astronomy is the photomultiplier tube (PMT). It is a combination of a conventional vacuum photocell with an electron multiplier. Such a system may be more sensitive than the sharpest vision, but it also has a limit. First of all, the photocathode has a small thermal emission. Enhanced millions of times, it becomes tangible, and therefore there is a current at the PMT output in the absence of light. Another limitation is imposed by the quantum structure of light: a flux of 1000 quanta per second can be measured quite easily, but the uneven arrival of quanta creates an additional shot effect. PMTs are manufactured with various types of cathodes, which allows them to be used for all parts of the range, except for the far infrared regions. PMTs are typically "single-channel" devices; they cannot convey the distribution of brightness over the points of the photocathode. On fig. 2 shows a diagram of an astronomical photometer. A disk with holes, rotated by a synchronous motor, modulates the luminous flux. A phase detector with a large time constant operates synchronously with the modulation, which makes it possible to separate the signal from the noise even when the signal-to-noise ratio does not exceed 0,001. A special software device makes control measurements, compares and then prints the result. This instrument was also created at the Abastumani Observatory.
Of great interest is the idea of a photoelectronic device that makes it possible to automatically track the stars with a telescope (photoguide). The PMT serves as a receiver in it. The photo guide (Fig. 3) was developed at the Leningrad Institute of Electromechanics.
Indispensable tools for astronomers are the thermocouple and the bolometer. They can be used in the range from visible light to submillimeter radio waves. There are no other devices of such broadband. A thermocouple is a miniature thermocouple, usually placed in a vacuum. The junction of two dissimilar wires is blackened in such a way that all the radiation incident on it is absorbed, slightly heating the junction. Thermal emf appears. which can be measured with a highly sensitive low-resistance galvanometer. The amplification of this emf. lamp circuits is difficult, since it is very small, and low resistance cannot be used without a converter. The use of transistor circuits with low input resistance is of great interest here, however, transistor noise introduces a complication. The bolometer consists of two small metal plates a fraction of a micron thick, which are also blackened and placed in a vacuum. The radiant flux to be measured is directed to one of them. In the electric bridge circuit, due to the change in the resistance of this plate, caused by its heating, an unbalance appears, proportional to the amount of absorbed radiant energy. The bolometer is also inertial, and the bridge has a low output impedance. These devices, most often used as receivers of infrared rays, are single-channel. True, a screen made of a light-sensitive mosaic of a semiconductor type (photoresistance) has recently been developed, which is a multichannel device. The sensitivity threshold of thermoelements and bolometers does not exceed 10-11 W at a time constant of about 1 second. The only "multi-channel" device of its kind, where the electronic flow carries information about the entire image at the same time, is an image intensifier tube (IOC). The semitransparent photocathode, as in the PMT, is deposited on the inner surface of the end face of the flask. Naturally, here the cathode also determines the spectral purpose: the antimony-cesium cathode works well in the green-violet and ultraviolet regions, the bismuth-cesium cathode covers the entire visible range, and the oxygen-silver-cesium cathode allows penetration into the near infrared regions. There are other types of photocathodes. Special electronic lenses, which are electric fields formed by special electrodes, direct photoelectrons to the anode, similar to beam focusing devices in kinescopes. This is done in such a way that the flow structure is not distorted and the image transfer is accompanied only by its reduction. The anode is a fluorescent screen where the image can be viewed or photographed. The purpose of image intensifier tubes is to increase the brightness of the image and, if necessary, convert it from the invisible, such as infrared, to the visible. The improvement of these devices has led to the creation of multi-stage image intensifier tubes, where the image brightness is consistently increased. Real for a three-stage image intensifier tube is a brightness increase of 60-120 times, while a single-stage image intensifier gives a gain of 6-15 times. In another case, it became possible to make fuller use of the light of the screen - the anode, for which the thickness of the flask in this place is reduced to tenths of a millimeter, and a photographic film is pressed against it from the outside ("contact image intensifier tube" or "photocontact tube"). Designs were also developed where the photographic plate was placed from the inside in place of the anode. However, to get it, it was necessary to break the flask. Even with a few records replaced by an ingenious contraption, this is too expensive. More recently, television astronomical systems have been used. In the Soviet Union, the most significant work in this direction was carried out by N. F. Kuprevich, a senior researcher at the Pulkovo Observatory. In the installation he created, the accumulation method is used, which consists in the fact that a weak image is projected for a long time onto the superorthicon photocathode in the absence of a sweeping beam. In this case, the potential relief "accumulates" on the corresponding electrodes of the tube. Then a single scan is turned on, and an image with a greatly increased brightness (of the same order as that of multi-stage image intensifier tubes) appears on the TV screen of a closed-circuit television system. A single sweep eliminates the hassle of photographing. Quite difficult to set up and operate, the television system has great potential. Thus, small details of images of astronomical objects on photographic plates always look blurry. This is explained by the continuous jitter of the images. A similar phenomenon is known to everyone by the twinkling of stars. The television system, by increasing the brightness, makes it possible to reduce the duration of the exposure, and, consequently, the "blurring" of images. The television system is essentially single-channel, but thanks to line-by-line decomposition, it is able to transmit images, which makes it similar to the image intensifier tube. In terms of threshold sensitivity, both of these receivers are inferior to a good PMT. Photoguide for automatic tracking of a star by a telescope From all that has been said, it is clear that modern science has placed very powerful technical means at the disposal of astronomers. It would seem that now there is no basis for dissatisfaction. However, it is not. It is known, for example, that now some astronomical observations are already being carried out without human participation - from satellites. The whole world saw photographs of the far side of the Moon taken by the "electronic astronomer" - the Soviet AMS, launched on October 4, 1959. Obviously, in this case, no other way was possible. It was also necessary to send an AMS to Venus, since the orbit of this planet is inside the orbit of the Earth and at the moments of approach to the Earth, it faces us with a dark, and therefore invisible side. Many important problems await their solution by taking astronomical instruments out of the earth's atmosphere. Take, for example, the planet Mars, our closest neighbor. The mystery of Mars (its "channels" and other details) haunts not only astronomers. Many riddles and other luminaries; even the moon has a lot of them. It would seem that one has only to look through a telescope with a high magnification and much will become clear. But in reality this is not so. Instead of clear contours of the planet, you will see a ball trembling like a candle flame in the wind, with continuously floating foggy spots. This is the influence of the earth's atmosphere, where air flows of different densities create a continuously changing refraction of light rays. Even with a very calm atmosphere, it is not possible to distinguish any small details of the images. However, trembling and flickering is only one side of the matter. The whole trouble is that the vast majority of the range of electromagnetic radiation does not reach the Earth's surface. Meanwhile, the study of this particular part of the range can give science no less than insight into the blind. That is why the removal of the observatory beyond the atmosphere - first to an artificial satellite, and then to the Moon - is an urgent need. It is also not difficult to understand that, using a small telescope, no matter how magnified it may be, it is impossible to distinguish fine details on the planets. This is also unthinkable because the so-called diffraction limit has an effect. For example, to distinguish details on the surface of the Moon 40 m in size, you need a telescope with an objective diameter of at least 65 cm. But large telescopes are so heavy that they bend under the influence of their weight. We have to increase the rigidity of the structure, which, in turn, increases the weight, etc. Is there a way out of this situation? Yes, I have. It consists in the fact that a large one - a telescope installed on a satellite will not weigh anything. Its rigidity can be reduced to a minimum, while the mass of the structure will be small and putting it into orbit will not cost too much. In the future, telescopes will apparently be more expedient to install on the Moon, where they will weigh 6 times less than on Earth. It can be said without exaggeration that such an "external observatory", equipped with modern electronic equipment and computers (they can be located on Earth), is capable of solving hundreds of today's problems in a short time. It is interesting to note that the night on the Moon is 29,5 times longer than the earth, as is the day. Therefore, it is possible to conduct observations there both day and night. On the Moon and in space it will be possible to use new open electronic devices; after all, the vacuum there is such as has never been achieved in any lamp. Finally, it is impossible not to mention one more problem that is now moving from the pages of science fiction novels to the laboratory of scientists. We are talking about cosmic radio emission of artificial origin. It will be important not only to accept it, but also to decipher it. Although there are predictions about the specific wavelength where these signals should be looked for, the entire range must be studied. The achievements of Soviet science and technology, the historical flights of Soviet passenger spacecraft, the greatest successes of our Motherland in the conquest of outer space clearly testify to how successfully the centuries-old dreams of mankind, plans that were recently considered utopia, are being realized in the Soviet Union. We are confident that the time is not far off when Soviet astronomers will be able to go to the Moon to observe and test hypotheses. Author: L. Xanfomality
▪ Astronomical instrument Observer
Artificial leather for touch emulation
15.04.2024 Petgugu Global cat litter
15.04.2024 The attractiveness of caring men
14.04.2024
▪ Diamond the size of a planet ▪ Thermoid converts heat into electricity
▪ section of the site Grounding and grounding. Selection of articles ▪ article Pedagogical psychology. Lecture notes ▪ article For what merits are musicians admitted to Club 27? Detailed answer ▪ article Labor collective and ways to create healthy and safe working conditions
Home page | Library | Articles | Website map | Site Reviews
www.diagram.com.ua |
We recommend interesting articles Section 
See other articles Section 
Latest news of science and technology, new electronics:
All languages of this page