The ideal absorber
An ideal blackbody absorbs all incident electromagnetic radiation. Its name does not imply that it cannot shine: in thermal equilibrium it both absorbs and emits radiation, and a hot blackbody can glow brightly. Real materials approximate the model only over suitable conditions and wavelength ranges.
References: [1]
Temperature and the spectrum
A blackbody emits a continuous spectrum, not only one colour. Increasing temperature raises total emission and shifts the wavelength-spectrum peak toward shorter wavelengths. Wavelength and frequency representations distribute intensity differently, so their peak positions must not be treated as interchangeable without conversion.
References: [1]
Planck’s radiation problem
Measurements of thermal spectra exposed problems with classical predictions, particularly at short wavelengths. Planck introduced quantized energy conditions proportional to frequency and obtained a successful radiation law. This was a starting point for quantum theory, rather than the immediate completion of modern quantum mechanics.
Using the model in observation
Thermal continua from stars can approximate a blackbody over useful ranges, allowing temperature estimates. Real spectra also contain absorption lines and material-dependent effects. Interpretation must distinguish continuum shape, spectral features and the observing band rather than infer a precise temperature from an uncalibrated photograph’s apparent colour.
References: [1]