Glossary term: 中天
Description: 在天文學中，中天是指天體通過觀測者當地子午線的時刻。當一個天體穿過子午線時，它要麼處於最高點，要麼處於最低點。
從觀測者的角度看，天球似乎是圍繞地球旋轉的。這意味著，天體在一天中的運行軌跡是圓形的。大多數天體從東方升起，在天空中移動到更高的位置，直到穿過子午線，然後在天空中移動到更低的位置，在西方落下。拱極天體是指距離天極之一足夠近的天體，觀測者可以在一個恆星日（略少於 24 小時）內看到其完整的圓形路徑。在任何情況下，天體到達最高點都是在穿過子午線的瞬間。到達最高點的瞬間被稱為上中天。12 個小時（恆星時）後，當天體位於天空最低點時（通常低於地平線），這一瞬間被稱為下中天。
由於中天是天體穿過觀測者當地子午線的時刻，因此也通常被稱為子午線經過或子午線穿越。天體的時角是相對於觀測者的當地子午線定義的，因此根據定義，上中天發生在時角為 0 時的瞬間，下中天發生在時角為 12 時的瞬間。
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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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