当光源的切向速度和视向速度都不为0时，在一定条件下光波波长不变。
When the tangential and radial velocity of light source both does not equal 0, the light-wavelength is changeless under certain condition.
进一步结合已知的星团距离和视向速度资料，计算了NGC 2244的三维空间运动速度，结果表明NGC 2244是一个典型的薄盘族星团。
Combined with the mean radial velocity and distance of the cluster, from the literature, the 3-d spatial velocity of NGC 2244 is also derived.
双重星系或天体系统，用动力学方法测定其质量时，观测到的视向速度和距离间距，都是各自值的投影值，可用统计方法，求出一个关于它们的平均投影因子。
Both of the observed radial velocity and separation being projective values, in order to determine the mass of binary galaxies the average projection factor may be derived by a statistical method.
双重星系或天体系统，用动力学方法测定其质量时，观测到的视向速度和距离间距，都是各自值的投影值，可用统计方法，求出一个关于它们的平均投影因子。
Both of the observed radial velocity and separation being projective values, in order to determine the mass of binary galaxies the average projection factor may be derived by a statistical method.
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