太阳视差是天文常数之一﹐ 确切的名称应该是太阳赤道地平视差。它可以定义为﹕ 式中是地球赤道半径﹐A 是地月系质心到太阳的平均距离﹐即天文单位。在雷达天文学问世以前﹐地月系质心到太阳的距离是通过测定太阳视差 来推算的。由于天文单位是量度太阳系内天体之间距离的基本单位﹐又是测定恒星三角视差的基线﹐几个世纪以来﹐测定太阳视差就一直是天体测量学中的重要问题。
太阳视差的测定现代已采用雷达和激光技术取得了更好的采用值。
The sun parallax measurement has been used in modern radar and laser technology to achieve a better use of the value.
由于金星离地球更近，所以它的视差角会更大。哈雷计算出，利用金星可以测量出太阳与地球之间的距离，误差为五百分之一。
As Venus was closer to the Earth, its parallax angle would be larger, and Halley worked out that by using Venus it would be possible to measure the Suns distance to 1 part in 500.
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