The Sun is the only celestial body in the solar system that can emit light and heat on its own, and the energy it releases comes from the fusion of hydrogen nuclei inside it, so how many degrees is the surface of this burning fireball? It is about 5500 degrees Celsius.
The highest known melting point in the world is the compound of hafnium, which is five-carbonized tetra-tantalum hafnium, which has a melting point of 4215 degrees Celsius. It can be seen that no known substance can withstand the scorching heat of the sun's surface, so how do we measure the temperature of the sun's surface? In fact, it relies on the infrared temperature measurement method, which can also be called electromagnetic wave temperature measurement method, and now the infrared thermometer we use to measure body temperature is actually the same principle. So why rely on infrared rays to measure the temperature of the surface of an object? What exactly is infrared?
Infrared is a type of light, a type of light with wavelengths between 760 nanometers and 1 millimeter.
Since infrared is light, we must start with the composition of light. The daylight we see on weekdays is basically white, but this is not because daylight itself is white, this white light is made up of a combination of light of multiple colors. After the rain, because the air is filled with tiny water droplets, and the light will refract when it hits the water, the daylight that originally appears white will be split into 7 different colors of light, which is the dispersion of light. The first person to discover the principle of dispersion of light was the famous physicist Newton. Newton shone a white light on the triangular prism, and after penetrating the triangular prism, the light changed from a white light to a layered colored light, and this light always appeared in the order of orange, yellow, green, blue, and purple.
Why does the white light turn into a colored beam of light after penetrating the prism?
Is it because white light originally contains light of different colors, or does the light have some kind of reaction with the prism that produces colored light? In order to get the answer, Newton converged the colored beams through the convex lens, and then let them pass through the triangular prism again, and the result was that the colored light re-converged into a white light, and it turned out that the white light was a composite light, which was composed of the light of various elements. When the white light shines on the prism or water, it will be refracted, and different lights have different refractive indexes due to different wavelengths, so after refraction they are separated in the order of red orange, yellow, green, blue, and purple, which is the dispersion of light.
Although Newton discovered the dispersion of light, he did not find infrared, and the person who discovered infrared was the later British astronomer Herschel.
Sunlight on the object will cause the object to heat up, since the sunlight can be dispersed into 7 colors, then which color of light can make the object heat up faster? To figure out the problem, Herschel conducted an experiment in which he dispersed daylight into a beam of colorful light, placed a thermometer in each place where the light was illuminated, and also placed a thermometer in front of the red light that was not illuminated. The results of the experiment were unexpected, and the fastest heating up was the thermometer in the front that was not illuminated by light. Why is that? In fact, the thermometer is not uninvalued, just the light that illuminates it, we can't see, this invisible light is infrared.
In later studies, people gradually found that all objects will radiate electromagnetic waves outward, and the wavelength of the electromagnetic waves radiated has a close relationship with the temperature of the object.
The higher the temperature of the object, the closer the electromagnetic waves radiating outward toward the short band. For example, most of the objects we see on a daily basis are not very hot, so the electromagnetic waves they emit are in the longer wavelength infrared band, so we can't see the light they emit, only with infrared night vision goggles. But if we keep heating an object, such as a block of iron, as its temperature rises, the electromagnetic waves it emits will enter the shorter wavelength of visible light, and we will see the block turn red, orange, and even yellow.
Since the power of the electromagnetic wave radiated outward by an object is related to temperature, how should the relationship between the two be described?
After research, the Austrian physicists Stefan and Boltzmann finally came up with a law, which is the "Stefan-Boltzmann law". According to this law, the radiated power per unit area of an object is equal to the absolute temperature multiplied by the "Strafan-Boltzmann constant", which is valued at 5.67X10∧-8. With this law, it is very easy to know the temperature of an object, you only need to measure the electromagnetic wave radiation power per unit area of the object, and then substitute the formula to calculate the temperature of the object, and the temperature of the surface of the sun is calculated in this way. Strictly speaking, this temperature measurement method should be called electromagnetic wave temperature measurement method, but because the objects we measure daily, such as the human body, the electromagnetic waves radiated are in the infrared band, so it is also called infrared temperature measurement method.