Home / Topics / Heat & Thermodynamics
Blackbody radiation
Intermediate
An ideal absorber and emitter.
blackbodyAn ideal blackbody absorbs all radiation and emits a characteristic spectrum that depends only on temperature. Explaining it led Planck to quantum theory.
Stars and furnaces approximate blackbodies.
Real materials have emissivity less than 1.
In more detail
A blackbody absorbs all radiation that falls on it and emits thermal radiation with a spectrum set only by its temperature. This spectrum, Planck's law, was key to the birth of quantum theory.
Real-world uses
- Stars and the cosmic microwave background approximate blackbody spectra.
- Calibrating infrared cameras uses blackbody sources.
- Physicists use blackbody radiation to estimate the temperature of the cosmic microwave background and of stars.
Open the interactive lesson, with simulation and quiz →
Frequently asked questions
Is anything a perfect blackbody?
No, but stars and some cavities are very close.
Why was it important?
Classical theory failed to explain it, which led Planck to quantum ideas.
Is a real object a perfect blackbody?
No, but many objects, such as the Sun, come close enough that the blackbody model is a very useful approximation.
Related topics in Heat & Thermodynamics
Stefan–Boltzmann law · Newton's law of cooling · Wien's displacement law · Ideal gas laws · Boyle's law · Charles's law