The structure of the sun is far from clear. Spectral analysis shows that of the 109 elements that have been found on the earth, in addition to 17 artificial elements, the remaining 92 elements are present in the sun, which also shows that the sun and the earth have a close relationship. The sun is the closest star to the earth. The distance between the sun and the earth is 1.49597892 × 108 km, the diameter of the sun is 1.392 × 106 km, which is 109 times that of the earth; the volume is more than 1.3 million times larger than the earth, and the average density of the sun is 1.4g/cm3. That is, it is 50% denser than water, and the internal density of the sun is about 160g/cm3, so the sun’s gravity is about 29 times larger than the earth’s gravity. In terms of mass, the material composition of the sun is 78.4% H; 19.8% He; and 1.8% metals and other elements in total. The physical properties of the sun and the earth are shown in Table 1 and Table 2.
It is generally believed that the sun is a huge fireball under high temperature and pressure, and its structure is shown in Figure 2-1. The structure of the sun can be divided into the following parts from the inside out.
(1) The solar nucleus This is the center of the sun and the area where thermonuclear reactions take place. The radius of the solar nucleus is 0.2Rd, which only accounts for about 20% of the sun’s radius, but it concentrates about half of the sun’s mass. , the temperature is as high as tens of millions of degrees, and the pressure is as high as hundreds of millions of atmospheres. Under the action of high temperature and high pressure, all substances can only exist in the form of ions. Therefore, in the solar nucleus, violent thermonuclear reactions are carried out all the time, and most of the solar radiation energy is generated in the thermonuclear reaction process and released in the form of convection and radiation.
(2) Absorption layer The outer layer of the solar nucleus is called the absorption layer, with a thickness of 0.6Rd. The temperature of the radiation layer is about 70×104°C, and the pressure is also several hundred thousand atmospheres. Since the energy radiated from the solar nucleus is emitted in the form of high-energy gamma rays, the radiation layer realizes energy transfer through the absorption and re-emission of these high-energy particles. It can take up to 1,000 years for photons to escape from the sun), and high-energy gamma rays are gradually converted into visible light and other forms of radiation through X-rays, extreme ultraviolet, and ultraviolet. Without the intermediary effect of the radiation layer, the sun would be an invisible celestial body that emits only high-energy rays
(3) Troposphere The point from outside the absorber layer to 1 times the diameter of the sun is called the troposphere. A large amount of convective heat transfer takes place in this zone. The temperature, pressure and density change gradients here are very large, and the material is always in a state of violent up and down convection. The low-frequency sound waves generated by the convection can be transmitted to the outer atmosphere of the sun through the photosphere.
(4) The part outside the troposphere of the photosphere is called the photosphere, with a thickness of 500km and a surface temperature of close to 6000°C, which is the average effective temperature of the sun. The temperature inside the photosphere increases with depth, and the transparency of the atmosphere is limited. There is limb dimming, and almost all visible light is emitted from this layer. The most prominent phenomenon on the photosphere is the sunspot, which is actually a low-temperature vortex with a strong magnetic field. Due to its relatively low temperature, about 4000°C, it looks “black” compared to the surrounding area, so called sunspots. Sunspot activity has a large impact on the climate and ecology of the Earth, and it usually encounters a peak of sunspot activity every 11 years. The sunspot activity affects the earth, that is, the activity of the photon group. There are also some rice-like air masses that do not change with time and are evenly distributed on the photosphere. They are hot air masses that rise from the troposphere to the photosphere. These air masses appear and disappear from time to time.
(5) Chromosphere layer The chromosphere layer is outside the photosphere layer, its thickness is about 2000km, it is almost transparent, it is usually invisible, it can only be observed during a total solar eclipse, or it can be observed with a special filter. The temperature of the chromosphere rises from thousands of degrees at the bottom to tens of thousands of degrees at the top. The rose-red tongue-like gas on the chromosphere rises like a fire, which is called a prominence. The large prominence is hundreds of thousands of kilometers above the photosphere. There are also countless high-temperature plasma small suns called needles. The needles can be as high as 9,000 km, about 1,000 km wide, and have an average lifespan of about 5 minutes. The projection of the prominence on the sun surface is called a sliver. Between the chromosphere and the corona, sometimes violent bursts called flares occur suddenly. When a flare erupts, the radiation flux from the radio band to X-rays will suddenly increase, accompanied by the eruption of a large number of high-energy particles and plasma, which has a great impact on the Earth’s space environment.
(6) Corona Outside the chromosphere is the silvery white corona extending into space. The corona is composed of various particles, including a part of solar dust particles, ionized particles and electrons, with a density of 10-6g/cm3 and a temperature of more than 1 million degrees. Sometimes the corona can stretch tens of thousands of kilometers into space, forming the solar wind, hitting the Earth’s atmosphere, producing magnetic storms or auroras, and affecting the Earth’s magnetic field and communications.