Moving around the nucleus are extremely tiny particles, called electrons, which revolve around the nucleus in much the same way as the nine planets do around the sun.

围绕着原子核运动的是一些极其微小的粒子，称为电子，这些电子围绕着原子核旋转，正像九大行星围绕着太阳旋转一样。

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The Sun is the hub of a huge rotating system consisting of nine planets, their satellites, and numerous small bodies, including asteroids, comets, and meteoroids.

太阳是一个巨大的旋转系统的中心，这个旋转系统由九大行星、它们的卫星和无数的小天体组成，包括小行星、彗星和流星体。

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Because when you think about the solar system, you might think about this picture here. And you would say, well, there are eight planets, maybe nine.

因为当你想到太阳系，你可能会想到这幅画面——你会说，嗯，总共有八颗行星，也可能是九颗。

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Pluto is the last of the nine familiar planets to be visited by a spacecraft and the program made a major discovery even before leaving the ground.

NPR: NASA Sends Spacecraft to Pluto

First, its orbit appears to run in the opposite direction from those of the nine known planets.

ECONOMIST: X marks the spot

"Make no mistake about it, " said Geoffrey Marcy of San Francisco State University, who has helped find nine of the 12 planets discovered since 1995.

CNN: Astronomers spy new neighbors outside solar system