Although the Sun is generally a relatively stable luminous gas sphere, its atmosphere constantly experiences localized violent activities. From the Earth's perspective, the bright Sun is occasionally shrouded in "shadows", and the originally flawless solar surface will develop some faint "freckles". The Sun's atmosphere can be divided into three layers from the inside out: the photosphere, the chromosphere, and the corona. What we directly observe from the Earth is the lowest layer, the photosphere. The chromosphere and corona can only be observed with the naked eye during total solar eclipses. The circular solar disk we usually see is the solar photosphere. The temperature of the photosphere is about 5,800 Kelvin, with an average density of only a few hundred millionths of that of water. However, due to its thickness of 500 kilometers, it is opaque. The photosphere appears smooth, but in reality, it is like a boiling sea of fire. Intense activities occur in the photosphere, and telescopes can observe dense structures like grains of rice on its surface, called granulation. These structures rise and fall like boiling porridge, but in fact, they are caused by violent convection of gases beneath the photosphere. The temperature of the granules is 300-400 Kelvin higher than the surrounding temperature, making them appear brighter against the background. Each granule has a diameter of about 1,000 kilometers, but it is highly unstable, with an average lifespan of only 5-10 minutes. Another famous activity phenomenon on the photosphere is sunspots. Sunspots are giant gas vortices on the photosphere, most of which are oval in shape. In fact, sunspots are not dark, but because the temperature in the center of sunspots is more than 1,000 Kelvin lower than that of the surrounding photosphere, they appear darker against the bright background. In reality, their temperature exceeds 4,000 Kelvin. If a sunspot were removed, its brilliance would be comparable to that of the full moon.
The layer of atmosphere just above the photosphere is called the chromosphere, which is not easily observed. During total solar eclipses, when the moon obscures the bright glow of the photosphere for an instant, people can observe a rose-colored brilliant glow on the edge of the solar disk, which is the chromosphere. The chromosphere is about 2,000 kilometers thick, and its material density and pressure are much lower than those of the photosphere. Flares often occur on the chromosphere, which is another complex and violent activity phenomenon in the solar atmosphere, manifested as sudden and rapidly developing local bright spots. The energy released by flares in just a few minutes to tens of minutes is comparable to the total energy released by the entire Sun in one second. Solar storms caused by flares can cause a large number of high-energy charged particles (totaling up to 1 billion tons) to sweep through interplanetary space at speeds of hundreds of kilometers per second. If the solar storm happens to be directed towards the Earth, it will have a significant impact on the space environment near the Earth. On the chromosphere, we can also see many rising flames, which are called "solar prominences". Solar prominences are rapidly changing activity phenomena on the chromosphere, and a complete solar prominence process typically lasts several tens of minutes. At the same time, the shape of solar prominences can be described as varied, some like floating clouds and smoke, some like waterfalls and fountains, and some like arched bridges, which are too numerous to list. The most spectacular is the eruptive solar prominence. Originally either calm or active solar prominences sometimes suddenly "erupt in anger", vigorously ejecting gaseous matter. Sometimes the ejected matter returns to the solar surface, forming a ring-like structure called an annular solar prominence.
During the brief moment of a total solar eclipse, we can often observe a large white-blue, soft and beautiful halo around the Sun, which is the outermost layer of the solar atmosphere - the corona. The shape of the corona is related to solar activity, and the corona also has an outward expansion movement, causing hot ionized gas particles to continuously flow out of the Sun and form the solar wind.