Glossary term: 赤經(RA)
Description: 赤經是赤道坐標系中的兩個坐標之一(另一個是赤緯),天文學家用以定義天體在天空中的位置。從地球看去,天空中的所有不同位置共同構成了一個以地球為中心的遙遠球面,稱為天球。天空中地球赤道正上方的點構成了天球上的天赤道,地理北極正上方的點就是北天極,而地理南極正上方的點就是南天極。就像地理學家在地球表面定義地理經緯度一樣,天文學家也可以在天球上定義經緯度。但如果我們將天體的經度坐標選擇為其正下方的點在地球表面上對應的地理經度值,那麼恆星的坐標值就會隨著地球的自轉而改變。為避免這一點,赤道坐標系的赤經是相對於一條不隨地球自轉改變,而相對於恆星固定不變的“子午線”來測量的。這條子午線的地位與地球上的格林尼治子午線類似。這條子午線與天赤道的交點定義為太陽從南天球運動到北半球的視軌跡與天赤道相交的確切位置。由此定義的經度稱為赤經,其數值自西向東增加。如果在地球上向天赤道看去,則隨著地球的自轉,所有的赤經值都會在約24小時內依次飛掠而過。因此,赤經通常用時間值來表示,用24小時來代替圓周的360度。赤緯是第二個赤道坐標,與地理緯度相對應。地球自轉軸的輕微擺動被稱為歲差,它使赤道坐標系——恆星和其他天體的赤經和赤緯——隨時間發生變化,但這種變化是非常輕微緩慢的。
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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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