这就是所谓的凌日行星。

It is what is known as a transiting planet.

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1677年11月，哈雷在南太平洋荒凉的圣赫勒拿岛上观测到了水星（最靠近太阳的行星）的凌日现象。

In November 1677, Halley observed a transit of the innermost planet, Mercury, from the desolate island of St Helena in the South Pacific.

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但是这样的凌日现象已经为被证明可能是宇宙中最重要的突破之一的说法铺平了道路，这个说法即找到那些围绕其他恒星轨道公转的和地球大小相似的行星。

But such transits have paved the way for what might prove to be one of the most vital breakthroughs in the cosmos—detecting Earth-sized planets orbiting other stars.

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