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A transit of Mercury across the Sun as seen from Venus takes place when the planet Mercury passes directly between the Sun and Venus, obscuring a small part of the Sun's disc for an observer on Venus. During a transit, Mercury can be seen from Venus as a small black disc moving across the face of the Sun. A central transit may last up over 8 hours, although presently transits' durations rarely exceed 7 hours (the last time it happened was in 1899, the next one will be in 2064). Transits of Mercury from Venus occur in an irregular fashion: sometimes there are several per decade, while on other occasions there are longer gaps. The overall frequency is less than the frequency of transits of Mercury from Earth. Naturally, no one has ever seen a transit of Mercury from Venus. The Mercury-Venus synodic period is 144.5662 days. It can be calculated using the formula 1/(1/P-1/Q), where P is the orbital period of Mercury (87.968435 days) and Q is the orbital period of Venus (224.695434 days). The inclination of Mercury's orbit with respect to Venus's ecliptic is 4.33°, which is less than its value of 7.00° with respect to Earth's ecliptic. The transit that occurred on March 22, 1894 was particularly interesting because on the 21st, when it began, there were also transits of Venus and of Mercury visible from Saturn. There was no overlap among the three transits, however. == Grazing transits == Sometimes Mercury only grazes the Sun during a transit. In this case it is possible that in some areas of Venus a full transit can be seen while in other regions there is only a partial transit (no second or third contact). The transit of October 25, 1344 was such a transit. The next such transit will occur on January 1, 2387. It is also possible that a transit of Mercury can be seen in some parts of Venus as a partial transit, while in others Mercury misses the Sun. Such a transit last occurred on May 21, 1027. The next such transit will occur on April 30, 3168. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Transit of Mercury from Venus」の詳細全文を読む スポンサード リンク
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