Glossary term: 軌道
Description: 軌道是在一個系統中運動的天體圍繞該系統質心的軌跡，由系統中天體之間相互施加的萬有引力引起。在太陽系等系統中，中心天體的質量遠大於其他天體，質心位於質量最大的天體（在太陽系中為太陽）內部或其附近。在雙星系統中，恆星軌道的質心通常位於兩顆恆星之間。
軌道的形狀通常呈橢圓形，系統的質心位於橢圓的一個焦點上。軌道的大小和形狀由橢圓的半長軸和離心率決定。離心率越大的軌道橢圓度越高。太陽系中大多數行星軌道的離心率都非常接近零，例如金星（0.007）和地球（0.017）。而離心率較大的例外有水星（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
This is an automated transliteration of the simplified Chinese translation of this term
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