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Glossary term: Electromagnetic Radiation

Also known as electromagnetic spectrum

Description: When 19th century physicists described electric and magnetic phenomena, they found that there is a way for patterns of electric and magnetic fields to propagate together through space at the speed of light, even in situations where there are no electric charges nearby. These waves are known as electromagnetic waves, or electromagnetic radiation. Elementary electromagnetic waves can be classified according to their wavelengths, and the resulting electromagnetic spectrum includes, from shorter to longer wavelengths: gamma rays, X-rays, ultraviolet, visible light, infrared, submillimeter, and radio waves (including millimeter/microwaves). Electromagnetic radiation from distant astronomical objects is astronomers' most important source of information about such objects.

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Term and definition status: This term and its definition have been approved by a research astronomer and a teacher

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".

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Related Diagrams


Three curves with radiation on the y-axis & wavelength on the x-axis. The cooler curves have redder & lower peaks

Blackbody Radiation

Caption: The curves of emitted radiation from blackbodies of different temperatures. The x-axis shows wavelength and the y-axis shows the amount of energy emitted every second by a square meter of the surface of that blackbody at each wavelength. The hotter the body, the shorter the wavelength and the bluer the light it emits its maximum amount of energy at. Despite the coolest body in this plot peaking in red light, the other hotter bodies all emit more red light than the coolest body.
Credit: IAU OAE/Niall Deacon

License: CC-BY-4.0 Creative Commons Attribution 4.0 International (CC BY 4.0) icons


Three curves with radiation on the y-axis & wavelength on the x-axis. The cooler curves have redder & lower peaks

Blackbody Radiation - UV Catastrophe

Caption: The curves of emitted radiation from blackbodies of different temperatures. The x-axis shows wavelength and the y-axis shows the amount of energy emitted every second by a square meter of the surface of that blackbody at each wavelength. The hotter the body, the shorter the wavelength and the bluer the light it emits its maximum amount of energy at. Despite the coolest body in this plot peaking in red light, the other hotter bodies all emit more red light than the coolest body. The dotted line shows the emitted radiation predicted by classical theory prior to modern quantum mechanics. This prediction tends to infinity at shorter wavelengths for any blackbody temperature above zero and was dubbed the ‘ultraviolet catastrophe’.
Credit: IAU OAE/Niall Deacon

License: CC-BY-4.0 Creative Commons Attribution 4.0 International (CC BY 4.0) icons

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