Solar radio astronomy is simply a subject that uses radio telescopes to observe and study the sun. The earliest radio astronomy almost originated from solar radio observations.
As early as 1869, the famous British theoretical physicist Maxwell proposed that stars can generate electromagnetic radiation in any waveband, including radio wave radiation. Some famous scholars, including inventor Edison and physicist Max Planck successively pointed out that the sun should be able to produce radio wave emission. In 1940, American scientist Grote Reber used a self-made 9.45-meter parabolic radio telescope to observe for the first time a strong solar radio signal at 162MHz. In 1942, the meter-wave gun sighting radar of the British air defense forces fighting the Germans suddenly received a strong signal interference from the sun. After analysis, it was found that the signal was closely related to the flare outbreak on the sun. The birth of solar radio astronomy.
Figure 1. American scientist Grote Reber (1911-2002), the earliest researcher on solar radio observations (source: Baidu)
As we all know, the minimum spatial resolution angle of a telescope is proportional to the wavelength and inversely proportional to the aperture of the telescope. Since the wavelength of radio waves is tens of thousands to tens of millions of times that of visible light, if we want to achieve the spatial resolution of optical telescopes, the aperture of radio telescopes is required to be tens of thousands to tens of millions of times that of optical telescopes! For the spatial resolution obtained by an optical telescope with a 10-centimeter aperture and a wavelength of 500 nanometers, the aperture of a radio telescope operating in the 10-centimeter band must reach 200 kilometers! This is a super project that is almost impossible to implement! Because of this, due to the limitation of the aperture, the solar radio images we have obtained so far are almost all blurry, far less clear and shocking than the solar optical images.
So, is solar radio astronomy irrelevant?
On the contrary, solar radio astronomy is not only very important,For many phenomena of solar eruption, it is almost the only research method!
We know that from time to time, the sun will have violent explosion events such as flares and coronal mass ejections. In addition to ejecting a large number of high-temperature plasma clouds, these events will also release huge energy, accelerate and emit a large number of high-energy charges. particle. The high-speed propagation of these high-energy particles in interplanetary space poses a serious threat to high-tech systems such as various spacecraft in orbit, space station, manned spaceflight, satellite communications, satellite navigation, and large-scale power grids on the ground. , Constitute a so-called catastrophic space weather event.
Our optical telescopes, including solar telescopes operating in the visible, ultraviolet and near-infrared bands, are almost invisible to these high-energy processes, especially the acceleration of high-energy particles and their propagation in space. However, in radio telescopes, these high-energy phenomena can be very prominently manifested in various radio bursts, such as solar radio bursts type I, type II, type III, type IV explosions, etc., among which, different types There are also a large number of fine spectral structures on the background of the explosion, such as zebra patterns, fibers, fish schools, quasi-periodic pulsations, and peak groups. These different types of solar radio bursts and different spectral fine structures correspond to the acceleration and propagation of non-thermal particles in different solar physical processes.
It can be seen from the comparison in Figure 2 that the radiation intensity of solar radio bursts is hundreds to millions of times stronger than the background radiation of the quiet sun and galaxy , and it has a very sensitive response. Therefore, we say that solar radio astronomy can detect solar eruptions that are simply invisible by other means. The combination of solar radio observations and other multi-wavelength observations is an important way to study the trigger mechanism, precursor characteristics, energy release mechanism, and particle acceleration mechanism of the celestial body plasma in the physical environment.
Figure 2. The solar radio burst compared with the background radiation of the quiet sun and the Milky Way (Source: Dulk, ARA&A, 1985)
In addition,Solar radio radiation occupies a very wide frequency range from submillimeter waves to kilometer waves, with a frequency span of more than 7 orders of magnitude. The corresponding radiation source area covers the solar photosphere, chromosphere, , corona, and interplanetary. Space can not only observe the high-energy particles produced by the solar eruption, but also track the propagation and evolution of coronal mass ejections and interplanetary shock waves in extremely thin interplanetary space. This is also difficult for other detection methods. . This is essential for the monitoring of disastrous space weather and space physics research.
Figure 3. Solar radio radiation covers the vast space from the sun to the vicinity of the earth (source: self-made)
source: National Astronomical Observatory of Chinese Academy of Sciences
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