Blackbody
A blackbody is an idealized physical body that absorbs all incident electromagnetic radiation, across all wavelengths and directions. It emits radiation in a characteristic spectrum that depends only on its temperature, not on its shape or composition. In practice, no real object is a perfect blackbody, but many systems approximate this behavior closely enough for experimental and theoretical use.
Planck's law describes the spectral radiance of a blackbody. The spectral radiance per unit wavelength is Bλ(T)
A perfect blackbody has emissivity ε = 1, meaning it is an ideal absorber and emitter. Real objects
The total power emitted per unit area of a blackbody is given by the Stefan-Boltzmann law: P/A
Historically, the concept arose from Kirchhoff's law of thermal radiation, and Planck's introduction of quantum theory
Applications include calibrating radiation detectors, radiometry, astrophysics, and climate science, where blackbody-like spectra serve as reference