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Great Conjunctions

6 Dec 2020, 20:37 UTC
Great Conjunctions
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During the early evening on December 21, Jupiter and Saturn will take part in a Grand Conjunction. The two planets will be separated by just 6 arc-minutes (1/5 the Moon’s diameter).

The excitement is growing with the upcoming Great Conjuction of Jupiter and Saturn on December 21, when they pass within 6 arc-minutes (1/5 the diameter of the Moon) of each other. You may be wondering how often close conjunctions of these two planets occur.

The short answer is that these planets are in conjunction every 19.6 years, on average, when Jupiter ‘overtakes’ Saturn in the sky due to the combined effect of Jupiter’s 11.9-year orbital period and Saturn’s 29.5-year orbital period. However, the apparent distance between the two at each conjunction varies greatly because they orbit the Sun in different planes.

For example, during the last Jupiter-Saturn conjunction (2020 May 31) the separation between the planets was 1.2 degrees (2.4 times the Moon’s diameter). A recent close conjunction (14 arc-minutes or 1/2 the Moon’s diameter) occurred on 1961 February 18.

To find a closer conjunction than this 2020 event, we have to go back to 1623 July 16 when the giant planets passed within 5 arc-minutes of ...

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