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Glossary term: Light

Description: Light is electromagnetic radiation that can be seen with the naked eye. The wavelength of light that can be seen by humans ranges from 380–750 nanometers; this is a narrow part of the electromagnetic spectrum that has a wide range of wavelengths from gamma (the shortest) to radio waves (the longest). The basic properties of light are intensity, direction of propagation, frequency, spectrum, and polarization. Its speed in a vacuum is estimated at 299,792,458 meters per second, and this is one of the fundamental constants of nature. The colour of light depends on its wavelength. Bluer light has the shortest wavelength in the visible spectrum, red has the longest. Light has multiple sources, natural and artificial; the main source of light that falls on Earth is the Sun. Light is emitted and absorbed in small "packets" called photons that can be studied as particles or waves. This property is called wave-particle duality.

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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".