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发表于 2012-6-6 07:15:34
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On June 5 2012, from about 6:00 p.m. onward until sunset, a truly rare event can be witnessed from many locations worldwide, including London, Ontario: the planet Venus will move in front of the Sun. Such an event is called a transit. Transits of Venus are truly rare events: the phenomenon has only been observed six times since Johannes Kepler first predicted a transit to occur in 1631, and the next one will happen only 105 years from now -- in 2117! It is one of the few events that give human beings a direct sense of the scale of the Solar System, and in fact, Venus transits have historically been used precisely to measure the distance scale of the Solar System.
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