It is generally believed that the sun is a huge gas mass under high temperature and high pressure, which can be divided into 6 regions from the inside to the outside.
①Solar core: The diameter of the solar core is about 0.23 times the diameter of the sun, the mass is about 0.4 times that of the sun, the volume is about 0.15 times that of the sun, the pressure is as high as 109atm (1atm=101325Pa), and the temperature is about 107K. In the thermonuclear reaction, 90% of the energy generated is radiated outward in the form of convection and radiation.
② Absorption layer: from outside the solar nucleus to about 0.8 times the diameter of the sun, it is called the absorption layer, also called the radiation layer. The pressure of this layer drops to 10-2 atm, and a large amount of hydrogen ions produced by the thermonuclear reaction are absorbed here.
③Troposphere: The troposphere is called the troposphere from the outside of the absorption layer to 1 times the diameter of the sun. The temperature during this period is about 5×103K, and a large amount of convective heat transfer is carried out in this area.
④Photosphere: Within 500km outside the troposphere, there are a large number of low-ionized hydrogen atoms, which are visible to the naked eye on the surface of the sun, and its brightness is equivalent to 6000K blackbody radiation. The photosphere is a very important layer. Most of the sun’s radiation is emitted from the photosphere. At the same time, there are sunspots and flares that have a great impact on the earth.
⑤Chromosphere layer: The thickness of the chromosphere layer is about 2500km, mostly composed of low-layer ammonia, hydrogen, and a small amount of ions. It is also called the solar atmosphere.
⑥Corona: Beyond the chromosphere is the silver-white corona that extends into space. The corona is composed of various particles, including some solar dust particles, ionized particles and electrons, and the temperature is as high as 106K or more. Sometimes the corona can stretch tens of thousands of kilometers into space, forming a solar wind, which impacts the earth’s atmosphere and produces a magnetic storm or aurora, which affects the earth’s magnetic field and communications.
The total annual energy consumption in the world is only equivalent to the energy projected by the sun on the surface of the earth within 40 minutes. The solar radiant energy comes from its internal thermonuclear reaction, and the energy converted per second is about 4×1026J, which is basically emitted in the form of electromagnetic radiation. The sun is usually regarded as a radiator with a temperature of 6000K and a wavelength of 0.3~3.0μm, and the distribution of radiation wavelengths ranges from the ultraviolet region to the infrared region. Although the solar radiation energy received by the earth is only one-2.2 billionth of the total radiation energy emitted by the sun into space, the solar radiation energy reaching outside the earth’s atmosphere is between 132.8~141.8mW/cm2, and after being reflected, scattered and absorbed by the atmosphere, about 70% of it is projected to the ground, it has reached 1.73×1015w. In other words, the energy that the sun shines on the earth every second is equivalent to 5 million tons of coal, which is tens of thousands of times the global energy consumption. The solar radiation received on the ground includes direct radiation and scattered radiation. The solar radiation that is directly received without changing its direction is called direct radiation; the solar radiation that changes its direction after being reflected and scattered by the atmosphere is called scattered radiation.
