Solar energy is the source of light and heat, and the source of all life on the earth. It gives all things light and warmth with endless energy. The energy used by mankind, whether it is fossil energy, biological energy or natural energy, comes directly or indirectly from the sun. All the food that humans eat contains the energy of the sun. It can be said that without the sun, there would be no things in the world.
1.1.1 Basic physical parameters of the sun
⑴ The volume is 1302500 times the volume of the earth.
⑵The rotation period is 25~30 days.
⑶The distance to the nearest star is 4.3 light years
⑷ 225 million years in the universe.
⑸The diameter is 139200km, which is 109 times the diameter of the earth
⑹ Radius 696,000km
⑺ Mass 1.989×1030kg
⑻The temperature is 5770℃ (surface), 15.6 million degrees Celsius (core).
⑼Total radiation power 3.83×1026J/s
⑽The average density is 1.409g/cm3, the density is only 1/4 of the earth
⑾The average distance between the sun and the earth is 150 million kilometers
⑿ The age is about 5 billion years.
1.1.2 The inner and outer layers of the sun
The biggest difference between the sun, the earth and the moon is that it is a huge glowing gas star, and it is a big hot balloon. Astronomers usually divide the sun into “inner three layers” and “outer three layers.” The inner three layers inside the sun”, from the center to the outside are the nuclear reaction zone, where the solar energy is generated; the radiation zone, which is the area that spreads solar energy outward; the convection zone, is the area that spreads the solar energy to the surface. Outside the sun There are “outer three layers”, the innermost is the photosphere, the middle is the chromosphere, and the outermost is the corona (Figure 1-1)
Figure 1-1 Schematic diagram of the sun structure
(1) The photosphere, the round surface of the sun that people usually see, is the photosphere. The thickness of the photosphere is about 500km, and the surface temperature can reach 5700℃. Due to the limited transparency of the atmosphere, there is a dim phenomenon in the observation.
Black spots often appear on the photosphere, which is actually a vortex with a strong magnetic field. Because of the low temperature, it looks black, so it is called a sunspot. If the sunspots can be taken out alone, a big sunspot can emit light equivalent to a full moon. The appearance of sunspots on the sun is constantly changing, and this change reflects the changes in solar radiation energy. There are complex periodic phenomena in the changes of sunspots, with an average activity period of 11.2 years.
There are intense activities in the atmosphere of the photosphere. With a telescope, you can see that there are many dense spot-like structures on the surface of the photosphere, much like rice grains, which are called rice grains. They are extremely unstable, generally lasting only 5~10min, and their temperature is 300~400℃ higher than the average temperature of the photosphere. It is currently believed that this kind of rice grain structure is caused by the intense convection of gas under the photosphere.
⑵The layer of atmosphere above the chromosphere layer is called the chromosphere layer. It is not easy to be observed at ordinary times. This area can only be seen during a total solar eclipse. When the moon obscures the bright brilliance of the photosphere, people can find a layer of rosy red brilliance on the edge of the sun, that is, the chromosphere layer, which has an average thickness of about 200km, and is a rosy, sparse and transparent atmosphere. Its chemical composition is basically the same as that of the photosphere, which is mainly composed of hydrogen, helium, and calcium plasma. From a distance, it seemed to be a burning prairie. However, the density and pressure of the substance in the chromosphere are much lower than those in the photosphere. In daily life, the farther away from the heat source, the lower the temperature, but the situation in the solar atmosphere is the opposite. The temperature at the top of the photosphere near the chromosphere is only 4300°C, and the temperature at the top of the chromosphere is as high as tens of thousands of degrees Celsius. , And further up, the temperature in the corona area suddenly rises to millions of degrees Celsius. People are puzzled by this abnormal warming phenomenon, and the exact reason has not been found yet.
At the edge of the chromosphere, there is often a sudden burst of flame-like air column, which can reach a height of tens of thousands of kilometers, or even more than 10 million kilometers, which is the so-called “prominence”. Prominence is a rapidly changing activity phenomenon, and a complete process of prominence generally takes tens of minutes. At the same time, the shape of the prominences can be said to be in various poses, some are like clouds and smoke, some are like waterfalls and fountains, some are like a curved arch bridge, and some are like tufts of grass. Astronomers divide the prominences into three categories: quiet prominences, active prominences, and eruptive prominences according to the scale of morphological change and the speed of change.
There are also flares on the chromosphere. It comes on fiercely, and goes quickly. In a very short period of time, it suddenly brightens, and at the same time it releases huge energy, which is equivalent to the energy produced by tens of thousands or even hundreds of thousands of hydrogen bomb explosions. The high-energy charged particle stream emitted by the flares interacts with the upper atmosphere of the earth to produce “aurora”. The outbreak of flares will interfere with the geomagnetic field (the compass fails, called a magnetic burst), the ionosphere will be destroyed, and it will lose its function of reflecting radio waves. Radio communications, especially short-wave communications, as well as television and radio broadcasts, will be affected. Thousand disturbances are even interrupted. In addition, it will destroy the power grid (which poses a great threat to grid-connected solar power generation), and may even threaten the lives of astronauts in space shuttles and space stations. Therefore, it is more and more important to monitor the solar activity and the intensity of the solar wind, and to make timely “space weather” forecasts.
The temperature of the chromosphere layer is increasing from the inside to the outside. From the innermost layer, that is, the part close to the photosphere layer, to the top of the chromosphere layer, it can increase from 4600K to tens of thousands of Kelvins, which emits invisible light. Mainly.In the short moment of the total solar eclipse, the corona layer can often be seen around the sun in addition to the gorgeous chromosphere, there is also a large white and blue, soft and beautiful halo. This is the outermost layer of the sun’s atmosphere- -Corona. The scope of the corona is above the chromosphere. Its shape is very irregular and changes frequently. The same chromosphere has no obvious boundaries. It is very thick and can extend to a range of 5 million to 6 million kilometers, that is, it extends to several solar radius distances. The material in the corona is not only thin, but also expands outwards, causing the thermally ionized gas particles to continuously flow out from the sun to form a “solar wind”. The brightness of the corona is very small, only one millionth of that of the photosphere, but the temperature is very high, reaching more than 1 million degrees Celsius. According to the difference in height, the corona layer can be divided into two parts: the height is below 170,000 kilometers, which is light yellow, and the temperature is above 1 million degrees Celsius, called the inner corona; the height is more than 170,000 kilometers, and the blue-white is called the outer corona. , The temperature is lower than the inner crown.
⑷The sun looks calm, but violent activities are actually happening all the time. Active phenomena in the sun’s surface and atmosphere, such as sunspots, flares, and coronal material eruptions, will greatly increase the solar wind and cause many geophysical phenomena, such as an increase in aurora, atmospheric ionosphere, and changes in geomagnetism.
1.1.3 The composition of the sun
Most of the substances that make up the sun are some ordinary gases. The main components are hydrogen and helium. Among them, hydrogen accounts for about 7.2% of the total volume of the sun, nitrogen accounts for about 27%, and other elements such as oxygen, magnesium, nitrogen, silicon, sulfur, and carbon. More than 60 elements such as silicon, copper, iron, diamond, and titanium account for only 1.8% of the total.