Glossary term: Thermal Radiation

Description: In a physical system that has reached what is called thermal equilibrium, each way the system can change (each "degree of freedom") has, on average, the same energy. The measure of how large that average energy is corresponds to the system's temperature. In a gas in equilibrium, for instance, all atoms have, on average, the same kinetic energy. Electromagnetic fields are a part of any physical system, and when a system reaches thermal equilibrium, some of its energy will be in the form of electromagnetic radiation with a characteristic spectrum. This radiation is called thermal radiation. For a system that can absorb and emit at all wavelengths, the resulting characteristic thermal radiation is called blackbody radiation. Its spectrum depends only on the system temperature.

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The OAE Multilingual Glossary is a project of the IAU Office of Astronomy for Education (OAE) in collaboration with the IAU Office of Astronomy Outreach (OAO). The terms and definitions were chosen, written and reviewed by a collective effort from the OAE, the OAE Centers and Nodes, the OAE National Astronomy Education Coordinators (NAECs) and other volunteers. You can find a full list of credits here. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".