Glossary term: 视向速度
Description: 当天文学家观测一个遥远的天体时，视向速度是天体沿观测者视线方向的运动分量 - 天体直接远离或直接朝向观测者运动。视向速度是利用多普勒效应测量的：对于向着我们移动的天体，光谱线会向较短的波长移动（蓝移）；对于远离我们的天体，光谱线会向较长的波长移动（红移）。视向速度总是相对于观测者而言的。高精度测量通常采用相对于太阳系质量中心（"质心"）的参考系来给出视向运动速度，以扣除地球绕太阳运动的影响。相互绕行的天体的视向速度随时间变化。当我们的视线方向恰好与轨道平面平行时，这种现象最为显著。在这种情况下，轨道运动会周期性地使每个天体轮流远离和靠近我们。即使天体本身无法被单独看到，也可以利用视向速度测量来推断这种轨道运动。由于质量越大，速度越快，这种测量可以用来估算轨道上天体的质量。这已被用于发现双星或环绕恒星运行的系外行星，以及重构星团和整个星系的质量。宇宙膨胀就是通过对星系距离和视向速度的系统分析发现的。
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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
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