This astronomical phenomenon has been used to explain what event? (click on the picture to see the animation)
Answer: The Star of Bethlehem had been conjectured (by Kepler, among others) to be caused by the conjunction of Jupiter and Saturn. The gif image above shows the night sky as it appeared looking south from Jerusalem on Nov. 12, 7 BC, 6 PM to 9:30 PM (via Wikipedia). Dinesh, matti tapaninen, Piyush Singh, and Jaggi got it.