Glossary term: 回归线
Description: 回归线是地球上的两条纬线圈：北回归线（位于北纬23°26′11.2″）和南回归线（位于南纬23°26′11.2″）。
相对于其他恒星和其他天体，太阳在天空中的位置在一年中会发生变化，看起来会在黄道星座中移动。从春分日到秋分日，太阳位于北天球。在夏至日的当地正午左右，太阳直射北回归线。从秋分日到第二年的春分日，太阳位于南天球。在冬至日的当地正午左右，太阳直射南回归线。在春分日和秋分日当天，太阳直射赤道上空。
地球上两条回归线之间的区域通常被称为“热带”。在热带地区，太阳每年有两天在当地正午时分直射赤道。
赤道南北两条回归线的纬度即为地轴相对于地球绕太阳运转的轨道的倾斜角度。
在西方，南北两条回归线分别以摩羯座和巨蟹座命名。这是因为在两千年前的冬至日和夏至日，太阳看起来会分别经过这两个星座。但由于地轴的进动，在如今的冬至日和夏至日，太阳不再出现在这两个星座中。
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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
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