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Glossary term: Period

Description: Numerous processes in astronomy are cyclic: they repeat regularly. An example is the orbit of a planet around the Sun, with the planet orbiting the Sun along the same trajectory again and again. The time it takes between one repetition of such a cycle and the next is called the cycle's period. The orbital period of a planet, for instance, is the time it takes the planet to go once around the Sun. The repetition does not need to be perfect, and orbital periods can change slowly over time. For instance, the slight systematic decrease in the period of the first binary neutron star provided the first indirect evidence for the emission of gravitational waves.

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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".