Glossary term: 视差
Description: 视差是由于观察者视点的变化，导致天体在天空中位置的表观变化。天空中的位置变化，以角度表示，是相对于我们所知道的最远的物体来确定的——过去是使用遥远的恒星；是被称为类星体的极其遥远的物体，它们确定了所谓的国际天球参考框架。视位置变化的角度与天体离我们的距离成反比，因此视差测量是确定邻域天体距离的有力工具（"视差法"）。对于太阳系天体，从地球上不同位置同时进行观测可以得到有效的视差值。对于恒星来说，视差角是观测者位置与视线成直角移动一个天文单位（地球-太阳平均距离）时的偏移值。观测者的位置移动量可以通过相隔几个月的观测来实现，在这几个月之间，地球沿着围绕太阳的轨道移动。根据定义，在这种条件下视差角为 1 弧秒的天体与地球的距离为 1 秒差距（3.26 光年）。在一年中，恒星在天空中的视位置会划出一个椭圆，其半主轴就是视差角。迄今为止最精确的恒星视差是由欧空局的盖亚任务提供的，盖亚任务是专门为这项任务设计的太空望远镜。
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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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