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Radio Astronomy
*** Please, subscribe to support… Electromagnetic (EM) radiation can be described in terms of a stream of mass-less particles, called photons, each traveling in a wave-like pattern at the speed of light. All objects above 0 Kelvin (-273 °C) emit energy in the form of EM radiation. It is called black body radiation. Electromagnetic radiation is also produced by non-thermal mechanisms like synchrotron radiation or astrophysical masers. By examining the energy emitted by celestial bodies, the distances and other properties of the celestial bodies can be determined. The telescope, word come from the ancient Greek, tele ”far” and skopein “to look”, is the basic tool we use to study the celestial bodies. We can observe celestial bodies with optical telescopes at visible wavelengths. However, celestial bodies emit energy not only in the visible area of the EM spectrum, but in all of them. At frequencies below the visible region; infrared and radio waves… At frequencies above the visible region; UV (ultraviolet), X-ray, gamma rays … The Earth’s atmosphere prevents most of the microwaves and ultraviolet radiation which are harmful for living beings. Visible light, some ultraviolet and infrared, and short wave radio to penetrate the atmosphere and bring information about the universe to us. In addition, EM radiation is prevented by the clouds of gas and dust that they encounter during their long journeys. Thanks to radio astronomy, celestial bodies called pulsars, some very distant quasars and dense nebulae can be examined. Cold irradiations, such as the dark nebulae and cosmic background radiation at a temperature of 3 °K (-270 °C), which is considered the residue of the Big Bang, can be detected by radio waves. The extraterrestrial radio waves were first discovered in 1931 by the American physicist Karl Jansky. The Jansky unit is used to express the power of radio waves: Jansky: Energy flux unit in radio astronomy SFU: Solar flux unit The power flux densities received from distant radio galaxies varies from micro-jansky to milli-jansky. Whereas a distant radio station may produce several millions of SFUs. Signals of radio astronomy is also small compared to the visual light. Thus, a radio telescope must have a large “collecting area,” or antenna, in order to be useful. The diameter of the collection area (mirror, lens, dish etc.) proportional by signal resolution. With the interferometer and some other methods, more than one telescope can act as a single giant telescope. Simply; thanks to atomic clocks, the radio signals recorded with precise timings, after phase correction, they stacked and the resolution is increased. Thanks to interferometry, enables Atacama Large Millimeter/Submillimeter Array (ALMA), which has 40 antennas with 8-meter diameters, to act as a single giant 16-km diameter telescope. (ALMA has 66 antennas.) Using the Very Long Baseline Interferometry (VLBI) technique, virtual telescope arrays can be created worldwide. Event Horizon Telescope (EHT), which has taken the photograph of the giant black hole in the center of the Messier 87 galaxy, consists of 8 telescopes in 6 different places of the world. The largest diameter available to EHT is between the distance of IRAM Radio Astronomy Institute in Spain and the South Pole Telescope in Antarctica. Telescope resolution limit determines how small a detail can be resolved in the image it forms. The resolution of the Hubble Space Telescope, ie the smallest area it can see, is 50,000 micro-arc-seconds (0.05 arc seconds). Resolutions according to mirror / lens diameters are approximately: When it’s finished, it’s going to be the world’s largest optical telescope. It is planned to have a 39 meter diameter primary mirror, each consisting of a combination of 798 hexagonal mirrors of 1.4 meters. Wavelength of visible light is in the 400-750 nm range, but radio waves have a longer wavelength of 1mm. This results in a very low resolution of a single radio telescope. Although the LMT radio telescope in Mexico has a 50 m diameter collection area, its resolution is between 4 – 20 arc-seconds, according to wavelenght between 0.85 mm to 4 mm. In Chile, the ALMA telescope array achieves the resolution of a 16 km diameter telescope, 0.016 arc-seconds (16-milli-second) despite at the long wavelength. EHT has a resolution of 20 micro-arc-seconds (0.00002 arc-seconds), creating a virtual telescope of 8,600 km. The data obtained by radio telescopes is in the unvisible area of the EM spectrum. Therefore, the colors used in images obtained with radio telescopes are not true colors. Photographs obtained by radio waves are colored for illustration purposes. The world’s largest radio telescope is a 500 meter diameter FAST telescope. It is in the province of Guizhou in southwest China. In addition, the SETI Institute, established in 1984, has been using the radio telescopes to trace the advanced civilizations of extraterrestrial. *** Please, subscribe to support…

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