Star radiation. Blackbody and Planck’s Law

Microwave background radiation

Star radiation should not be confused with microwave background radiation. Microwave background radiation is homogeneous microwave radiation that permeates the entire universe, being the remnant of the Big Bang. Although both star radiation and microwave background radiation are forms of radiation, star radiation is emitted continuously by present-day stars, while microwave background radiation is a relic of the early universe, observable in the microwave region and virtually unchanging in time.

Blackbody radiation. Planck’s Law

A blackbody is a theoretical object that absorbs all radiation incident on it and emits radiation continuously as a function of its temperature. The radiation emitted by a black body is called black body radiation and its value is established by Planck’s Law.

Stars behave very much like a black body, absorbing the radiation that reaches their surface and emitting radiation in the form of light and heat. The temperature of a star determines the spectrum of radiation it emits. Wien’s displacement law states that the hotter a star is, the shorter the dominant wavelengths in its radiation spectrum. Therefore, hot stars emit a greater proportion of radiation in the ultraviolet and visible wavelength range. Cooler stars emit a greater proportion of radiation in the infrared wavelength range.

In addition to temperature, star radiation also depends on the composition of the stars. The constituent elements affect the absorption and emission of radiation at specific wavelengths, resulting in different radiation spectra. The study of these spectral lines allows astronomers to determine the chemical composition of stars and to obtain information about their temperature and other characteristics.