So, I want to tell you a bit about Kepler's second law of celestial mechanics.

因此我想告诉你们，一些关于开普勒第二定律的知识。

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Kepler's second law means that a planet's orbital speed changes with its distance from the sun.

开普勒第二定律指行星的轨道速度与其和太阳的距离。

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So, what Kepler's second law says is that the motion of planets is, first of all, they move in a plane.

开普勒第二定律说到，首先每个行星的运动都保持在同一平面内。

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