一般一个完美圆周的偏心值为0，而约有一半的系外行星的偏心值在0.25或者更高。

Where a perfect circle has an eccentricity value of zero, roughly half of exoplanets seen thus far have an eccentricity of 0.25 or greater.

youdao

这是一个向量场，其中旋转轨道是，以z轴为圆心的圆周，并且这个向量场与每个圆相切。

That is a vector field in which the trajectories are going to be circles centered in the z-axis and our vector field is just going to be tangent to each of these circles.

youdao

Whenever you see a particle moving in a circle, even if it's at a constant speed, it has an acceleration, v square over r directed towards the center.

只要看到质点做圆周运动,即使是匀速圆周运动,也存在一个加速度,大小为 v^2 / r,方向指向圆心

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