The goal was to measure the AU; then, knowing the orbital speeds of all the other planets around the Sun, the scale of the Solar System would fall into place.

目标是测量 AU；随后，当我们知道了所有围绕太阳的其他行星的轨道速度，对太阳系的规模就有充分的认识了。

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If the Sun was at the center of the universe, things would fall toward the Sun and away from the Earth, which of course they didn't.

如果太阳在宇宙的中心，物体就会离开地球向太阳落去，但事实显然没有。

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Day and night would each be exactly 12 hours long on a spring or fall equinox only if the sun were a single point of light and Earth had no atmosphere.

如果想要昼夜在春秋分日达到精确地12小时等长，除非太阳是个单点光源或者地球上没有大气层。

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Japanese space agency (Jaxa) scientists want to detect a measurable acceleration in the spacecraft as photons - the particles of light - from the Sun fall on the roughly 200-sq-m, ultra-thin sheet.

BBC: Mini-camera pictures Japan's Ikaros solar sail

This shield does not stop all the cosmic rays from getting though, and its effectiveness varies with the long-term changes in the activity of the Sun, which can rise and fall on a timescale of centuries.

BBC: Viewpoint: The Sun and climate change

Careful positioning of the sail should slow the probe down, causing it to fall towards the sun.

ECONOMIST: Rockets are not the only way to travel through outer space