Glossary term: 轨道
Description: 轨道是在一个系统中运动的天体围绕该系统质心的轨迹，由系统中天体之间相互施加的万有引力引起。在太阳系等系统中，中心天体的质量远大于其他天体，质心位于质量最大的天体（在太阳系中为太阳）内部或其附近。在双星系统中，恒星轨道的质心通常位于两颗恒星之间。
轨道的形状通常呈椭圆形，系统的质心位于椭圆的一个焦点上。轨道的大小和形状由椭圆的半长轴和离心率决定。离心率越大的轨道椭圆度越高。太阳系中大多数行星轨道的离心率都非常接近零，例如金星（0.007）和地球（0.017）。而离心率较大的例外有水星（0.206）和矮行星冥王星（0.244）。
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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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