Glossary term: 天顶
Description: 天顶定义为观测者正上方的一点，因此这个点随着观测者位置的变化而变化。例如，对位于伦敦、北京与开普敦的观测者来说，他们的天顶是各不相同的。若用角度来度量，则天顶与观测者的地平线成90度。天顶角定义为天体与天顶之间的角距离。位于天顶的天体的天顶角为0度，而位于地平线上的天体的天顶角为90度。与天顶相对的一点，即观测者的正下方，称为观测者的天底。如果地球是一个完美的球体，那么观测者的天顶和天底之间的连线就会穿过地心，但实际上地球只是近似于球体，因此地心与这条连线通常有一定的距离。
Related Terms:
See this term in other languages
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".
