Glossary term: 极圈

Description: 极圈是地球上两条特定的纬线圈。位于北纬66°33′48.8″的极圈称为北极圈，位于南纬66°33′48.8″的极圈称为南极圈。由于地球自转轴是倾斜的，北极圈以北和南极圈以南地区的冬季为“极夜”，夏季为“极昼”。极夜期间，太阳在地平线以下的时间超过24小时，暗夜可持续数月。极昼期间，太阳在地平线以上的时间超过24小时，白昼可持续数月。越靠近极点，则极昼和极夜最长。对于每个极地区域，极夜出现在冬至前后，极昼出现在夏至前后。

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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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