Glossary term: 时间
Description: 我们每个人对时间都有一个基本的概念：从过去到现在，再到未来，事件一个接一个地发生。然而，时间并不是看得见、听得到、闻得到、摸得到或尝得到的东西。不过，它是可以测量的，而这正是时间在天文学和物理学中的重要性所在。
我们测量时间的方法是，将正在发生的事情的持续时间与时钟上测量的持续时间进行比较，或者，对于较长的时间，与日历上测量的持续时间进行比较。传统上，这种时间测量是以地球自转为基础的。地球自转一圈所需的时间（根据太阳的位置判断）就是一天的长度。通常的会讲一天分为 24 小时，每小时分为 60 分钟，每分钟分为 60 秒，这提供了额外的时间单位。
自 1967 年起，时间的定义改用铯-133 原子钟测量的一秒时间（"SI 秒"）。在此基础上定义了几种时间系统，特别是世界时间（UTC），它被用于全世界的官方计时；还有所谓的儒略日及其变体，它是天文学中使用的一种连续计数天数的方法。
爱因斯坦的狭义相对论和广义相对论表明，时钟上流逝的时间既取决于时钟的运动，也取决于重力的影响。这些相对论效应需要在高精度的时间测量中加以考虑，例如使用全球定位系统（GPS）卫星进行的测量。
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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
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".
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