最后，科学家测量了由于行星的引力拖拉而产生的恒星摆动，这就是径向速度。

Finally, scientists measure the star's wobble due to the planet's gravitational tug, known as the radial velocity.

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是为了让火箭的速度足够快，足以逃离地球的引力。

It is to get the rocket going fast enough to escape Earth's gravity.

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逃逸速度就是一个物体的速度，比如说，从加农炮中射出的最小初始速度，这样这个物体以后就可以自己脱离地球的引力。

Escape velocity is simply the speed of an object that's shot out of a cannon the minimum initial speed so that the object could later escape Earth's gravity on its own.

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