Spectral classes – classification of stars by their emission spectrum, primarily by the temperature of the photosphere. The differences in the spectra of stars are due to the difference in the physical properties of their atmospheres, mainly in temperature and pressure (which determine the degree of ionization of atoms). The type of spectrum also depends on the presence of magnetic and interatomic electric fields, differences in chemical composition, rotation of stars, and other factors.
Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.