All things grow by the sun. With its brilliant light and great energy, the sun gives light, warmth and life to human beings. The relationship between the sun and human beings could not be more intimate. Without the sun, there would be no day; without the sun, all living things would die. The energy used by human beings, whether it is coal, oil, natural gas, or wind and water power, all come directly or indirectly from the sun. All food eaten by human beings, whether animal or vegetable, contains the energy of the sun. It can be said that the sun is the source of light and heat, and the source of all life phenomena on earth. Without the sun, there would be no human beings.
So, what is the sun like, how far is it from us, how big is it, what is it made of, and what is its structure?
The sun we see with the naked eye hangs high in the blue sky. However, in fact, the sun is a huge spherical hot air mass, and the entire surface is a sea of boiling fire, which is extremely unstable, and is constantly undergoing thermonuclear reactions all the time. According to the research and exploration of scientists, the sun can be divided into two parts: atmosphere and interior.
The structure of the sun’s atmosphere has three layers, the innermost layer is the photosphere, the middle is the chromosphere, and the outermost is the corona (see Figure 1).
(1) Photosphere layer
The radiant, smooth mirror-like circular surface that people usually see is the photosphere layer. It is the lowest layer in the solar atmosphere, that is, the layer closest to the interior of the sun, with a thickness of about 500km, accounting for only about 7/10,000 of the radius of the sun, and is relatively thin. Its temperature is around 5700K, and the sun’s brilliance is basically emitted from here. Its pressure is only 1% of atmospheric pressure, and its density is only a few hundred millionths of water.
(2) Chromosphere layer
During a total solar eclipse, a beautiful colored ring can be seen around the moon wheel, which is the chromosphere of the sun. It is located outside the solar photosphere and is a sparse and transparent layer of the solar atmosphere, mainly composed of hydrogen, helium, and calcium plasma. The thickness varies from place to place, with an average of about 2000km. The temperature is higher than that of the photosphere. From 4600K at the top of the photosphere to the top of the chromosphere, the temperature can increase to tens of thousands of degrees, but the total amount of visible light it emits is not as good as the photosphere.
(3) Coronal layer
During a total solar eclipse, we can see a silvery-white ring of varying thickness around the sun, which is the corona. The corona is the outermost layer of the sun’s atmosphere, and beyond it lies the vast interplanetary space. The shape of the corona is very irregular and changes frequently, and the chromosphere has no clear boundaries. Its thickness is not uniform, but it is large and can extend to a range of 5 to 6 million kilometers. It is made up of extremely rare materials, only a few million times as dense as Earth’s upper atmosphere. The brightness is also very small, only one millionth of that of the photosphere. But its temperature is very high, reaching more than 1 million degrees Celsius. According to the different heights, the corona can be divided into two parts: the inner corona with a height of less than 170,000 kilometers, which is pale yellow and has a temperature above 1 million degrees Celsius; the outer corona with a height of more than 170,000 kilometers is called the outer corona, which is bluish-white and slightly lower in temperature than the inner corona.
The material of the sun is almost all concentrated in the interior, and the proportion of the atmosphere in the total mass of the sun is extremely small, which can be said to be insignificant. The outermost layer inside the Sun, immediately following the photosphere, is the troposphere. The gas in this area is often in a state of convection that rises and falls. Its thickness is about tens of thousands of kilometers.
Scientists have initially revealed the chemical composition of the sun using solar spectroscopy. Among the 92 natural elements that exist on earth, 68 have been discovered successively on the sun. The main components of the sun are hydrogen and helium. The volume of hydrogen accounts for 78.4% of the volume of the entire sun, and the volume of helium accounts for 19.8% of the volume of the entire sun. In addition, there are more than 60 elements such as oxygen, magnesium, nitrogen, silicon, sulfur, carbon, calcium, iron, sodium, aluminum, nickel, zinc, potassium, manganese, chromium, cobalt, titanium, copper, and vanadium. But they account for a very small proportion, only 1.8%.
The sun is the closest star to the earth. The average distance between the earth and the sun, the latest accurate value is 149 598 020km, generally 150 million kilometers.
When viewed with the naked eye, the size of the sun and the moon are about the same size as a large disc. But in fact, the size of the sun is extremely huge, it is a huge planet. According to the most accurate measurement so far, the diameter of the sun is 1392 530 km, which is generally 1.39 million km, which is 109.3 times larger than the diameter of the earth and 400 times the diameter of the moon. The volume of the sun is 1.412 2×1018km3, which is 1.3 million times that of the earth. We see the sun and the moon about the same size with the naked eye because the average distance from the moon to the earth is only one-fourth of the distance from the sun to the earth.
The mass of the sun is estimated to be about 1.989 2 × 1027 t, which is equivalent to 333 400 times the mass of the earth.
The density of the sun is very uneven, small outside and large inside, gradually increasing from the outside to the inside. The central density of the sun is 160g/cm3, which is 8 times the density of gold, which is quite large; but its outer density is extremely small. As far as the entire sun is concerned, its average density is 1.41g/cm3, which is nearly half the density of water (at 4℃), and only 1/4 of the earth’s average density of 5.58g/cm3.
This is what the sun looks like.