How do we know that the Earth is a smaller ball turning around one of those stars, the Sun?

我们怎么知道地球是一个更小的球，绕着其中一颗恒星——太阳转呢？

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The earth would be a frozen ball if it were not for the radiant heat of the sun.

要是没有太阳的辐射热，地球将会是一个冰冻的球体。

《柯林斯英汉双解大词典》

All the gravity of all the mass in the cosmos should have been pulling the universe back inward, just as gravity pulls a ball back down to Earth after it's been thrown into the air.

宇宙中每一物体的每个引力都会对宇宙产生一个指向物体本身的拉力，就像在重力作用下，抛向空中的球会被拉回地面。

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The first pictures of Earth taken from space showed a solid ball covered by brown and green landmasses and blue-green oceans.

VOA: special.2011.01.04

On Oct. 4, 1957, a primitive, 100-pound metal ball was sent hurtling into orbit around Earth, beeping back radio signals like taunts.

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Moreover, we know that Earth, once a fiery ball, has cooled and gained life upon its surface with static, non-thinking plants and mobile, thinking animals.

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