Blackbody Radiation: Observation, Measurement & Evidence

A blackbody spectrum has a smooth distribution with a temperature-dependent peak. Wien's law links temperature to the wavelength of maximum emission, while the Stefan-Boltzmann law says emitted power per unit area grows as the fourth power of absolute temperature.

Laboratory cavities approximate blackbodies, and stellar spectra show temperature-dependent continuum shapes. The Sun's photospheric continuum corresponds roughly to a temperature near 5800 K even though absorption lines are superimposed.

Thermal motion in matter produces a distribution of electromagnetic emission. Raising temperature increases the total emitted energy and shifts the peak toward shorter wavelengths because higher-energy modes become more strongly populated.

Astronomers compare calibrated multi-band fluxes or spectra with blackbody curves to estimate temperature and emitting area. Deviations are scientifically valuable: stellar absorption lines, dust emissivity, atmospheric molecular bands, and optically thin plasma can all depart from an ideal Planck curve. A temperature estimate therefore requires knowing which part of the spectrum is measured and whether extinction or multiple thermal components are present.