Due to the differences in age and mass, the surface temperature of each star varies greatly. The surface temperature of a star is usually expressed by an absolute temperature scale, generally between 2000 and 40000. Stars with different surface temperatures show different colors, such as brownish red at low temperature, yellow at high temperature, blue and white at high temperature.
Everyone has seen the rainbow after the rain. It is a colored light band composed of seven colors: red, orange, yellow, green, cyan, blue and purple. It is very beautiful. If possible, we can do an experiment: let a beam of sunlight enter a dark room, pass through a prism, and then project it onto a white screen. At this time, you will see that there is no white sunshine on the screen, but a colorful light band, just like a rainbow after rain, showing various colors of red, orange, yellow, green, cyan, blue and purple. This phenomenon shows that white light is composed of these seven colors of light. This beautiful seven-color band is called solar spectrum, also called continuous spectrum. Look carefully, there are many dark lines with different thickness and uneven distribution on the continuous spectrum, which are called absorption lines. There are many bright lines, called emission lines. These spectral lines represent different elements in the composition of the sun.
The stars are distant suns. What are the similarities and differences between the spectra of stars and the light spectra of the sun?
Sunlight is white, and the light of stars has various colors, including red, yellow, white and blue. The ancients have discovered this. They call antares "fire" because they see that antares are red. Why are the colors of the stars different?
We can see a burning coal stove. When coal just started burning, the fire was red. As the fire gets bigger and bigger, the color of the fire gradually changes from red to yellow, then to white and finally to blue. Obviously, the temperature of Honghuo is low and that of Lan Huo is high.
The same is true of stars. We can judge the temperature of a star from its color. The temperature of a star is usually expressed by the absolute temperature K. The conversion relationship between absolute temperature and celsius temperature is OOC = 273 K. Stars with surface temperature above 30000 K emit blue light, stars with surface temperature of 1000-300 OOK are blue-white, and stars with surface temperature of 7500- 1000-300 OOK are pure white. ..
The spectrum of a star is the same as that of the sun. In addition to the continuous spectrum of color, there are linear spectra representing various elements that make up a star. By measuring and analyzing these spectral lines in the star spectrum, people can obtain the information of chemical composition of each star. From the spectral experiments in the earth laboratory, we know that the spectral lines of light elements such as hydrogen, oxygen and carbon are mainly in ultraviolet, which is invisible to the naked eye. Only a few spectral lines are in the visible region, and most of the spectral lines of heavier elements are in the visible region. By comparing the spectral lines of stars with those of various substances known in earth experiments, we can determine what chemical composition there is in stars. The intensity of spectral lines is not only related to the content of elements, but also related to the temperature and pressure of the star atmosphere. Astronomers classify stars into the following types according to their temperature and spectral characteristics:
Type O is a blue star with obvious ionized nitrogen lines in the spectrum, and the representative stars are Betelgeuse and Akisaka.
Type B is a blue and white star with obvious neutral nitrogen spectrum. For example, the three stars on Orion's belt on the right belong to type B stars.
Type A is a white star with obvious hydrogen spectrum, and Vega and Sirius belong to type A stars.
Type F is a yellow and white star with obvious ionized calcium spectrum, and Polaris belongs to type F;
G-type is yellow star, neutral metal line is dominant, and the sun is a typical G-type star;
K-type is an orange-red star, which is densely distributed with spectral lines of many metals and other elements. Arcturus in Capricorn is a K-shaped star.
M-type is a red star, and molecular spectral lines can be seen. Scorpio's big Mars is an M-shaped star.
Surface temperature (k) 40000-30000 30000-1000010000-7500 7500-6000 6000 5000-3500 3500-25000.
Spectrum O B A F G K M
Color blue blue white yellow white yellow orange red.