但有一个问题：和水星凌日不同的是，金星凌日是罕见的，大约每隔一百年会成对出现八年的时间。
But there was a problem: transits of Venus, unlike those of Mercury, are rare, occurring in pairs roughly eight years apart every hundred or so years.
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.
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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