Glossary term: 周期
Description: 在天文学中，许多过程是周期性的：它们定期重复。例如，行星绕太阳的轨道就是如此，行星沿着相同的轨迹一次又一次地绕太阳运行。一个周期的一次重复过程开始到下一次重复过程开始所需的时间被称为周期。例如，一个行星的轨道周期就是行星绕太阳转一圈所需的时间。重复过程不需要是完美的，轨道周期可以随着时间的推移缓慢变化。例如，通过对双中子星周期逐渐减小的观测提供了引力波辐射的第一个间接证据。
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Term and definition status: The original definition of this term in English have been approved by a research astronomer and a teacher The translation of this term and its definition is still awaiting approval
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