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.

Related Terms:

• Frequency
• Orbital Period
• Gravitational Waves

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

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