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A triple conjunction is an astronomical event, where two planets or a planet and a star meet each other three times in a short period either in opposition or at the time of inferior conjunction, if an inferior planet is involved. The visible movement of the planet or the planets in the sky is therefore normally prograde at the first conjunction, retrograde at the second conjunction and again prograde at the third conjunction. The meeting of three planets is referred to as a particular case of syzygy. There are three possible cases of triple conjunctions. == Triple conjunctions between Mercury and Venus == At nearly every inferior conjunction there is a triple conjunction between Mercury and Venus. In most cases the second conjunction is not visible, because both planets have a too small elongation from the Sun. Triple conjunctions between Mercury and Venus are also possible, if Mercury and Venus are at the same time in inferior conjunction. This event is much rarer and the second conjunction between Mercury and Venus is also invisible. 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「Triple conjunction」の詳細全文を読む スポンサード リンク
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