Greatest conjunction
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Greatest conjunction is a term applied in astronomy to a conjunction of the planets Jupiter and Saturn at or near their opposition to the Sun. In this scenario, Jupiter and Saturn will occupy the same position in right ascension on three separate occasions over a period of a few months.
The so-called "Star of Bethlehem" — thought to have appeared c. 6 BC — was theorized to be a greatest conjunction; and some went so far as to assert that it was an occultation of Saturn by Jupiter, with the two planets appearing to merge into a single object as seen from Earth. However such an event did not take place at historic times. At the greatest conjunction in 6 BC, which is said to be that was the "Star of Bethlehem", the minimum distance between Jupiter and Saturn was around 1 degree, this is twice the Moon's diameter. The next occultation of Saturn by Jupiter will take place in 7541. There is no obvious period for the occurrence of greatest conjunctions: the last greatest conjunctions took place in 1682/83, 1821 (only in right ascension), 1940/41 and 1981, while the next one will take place in the year 2238/39!