Glossary term: Photon

Description: The term photon comes from the Greek phōs, which means light, and is therefore used synonymously and interchangeably with light. When astronomers refer to light, they are referring to all types of electromagnetic radiation from radio waves all the way to gamma rays.

A photon is a fundamental particle, carrier for the electromagnetic force, and considered to be the smallest packet (quanta) of electromagnetic energy. The quanta of energy associated with a photon of given frequency is proportional to this frequency and inversely proportional to its wavelength.

Modern views consider a photon as being not only a particle but also a wave. In astronomy, photons are foundational to our ability to observe and measure various aspects of the Universe and the objects it contains.

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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".