Great conjunction

A great conjunction is a conjunction of the planets Jupiter and Saturn.^{[Note 1]} The last great conjunction took place on May 31, 2000, while the next one will be in late December 2020. Great conjunctions take place regularly, every 18–20 years, as a result of the combined ~12-year orbital period of Jupiter around the Sun, and Saturn's ~30-year orbital period. The 2000 conjunction fell within mere weeks after both had passed conjunction with the Sun, and it was very difficult to observe without visual aid because the two planets rose only 30–45 minutes before sunrise, depending upon the location of the observer.

A greatest conjunction is a conjunction of 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. Such tripled occurrences are actually known as triple conjunctions.

In the years 1800 to 2100

As omens

Great conjunctions have attracted considerable attention as celestial omens. There has been some speculation, for example, that the so-called "Star of Bethlehem" was a great conjunction that occurred c. 7 BCE.^[1] During the late Middle Ages and the Renaissance, great conjunctions were a topic broached by most astronomers of the period up to the times of Tycho Brahe and Kepler, by scholastic thinkers as Roger Bacon^[2] or Pierre d'Ailly,^[3] and they are mentioned in popular and literary writing by authors such as Dante^[4] or Shakespeare.^[5] This interest is traced back in Europe to the translations from Arabian sources, most notably Albumasar's book on conjunction.^[6]

As successive great conjunctions occur nearly 120° apart, their appearances form a triangular pattern. In a series every fourth conjunction returns after some 60 years in the vicinity of the first. These returns are observed to be shifted by some 7–8°, so no more than four of them occur in the same zodiacal sign. To each triangular pattern astrologers have ascribed one from the series of four elements and thus four triplicities or trigons are formed. Particular importance has been accorded to the occurrence of a great conjunction in a new trigon, which is bound to happen after some 200 years at most.^[7] Even greater importance was attributed to the beginning of a new cycle after all fours trigons had been visited, something which happens in about 800 years. Since each 'element' (trigon) consists of 3 signs it takes 800x3=2400 for the whole process to start anew (relation with the cycle of Precession).

Kepler's trigon, a diagram of great conjunctions (from the book De Stella Nova (1606) by Johannes Kepler)

Originally a trigon was thought to last 240 years, and the full cycle 960 years; but later more correct estimation were provided by the Alphonsine tables.^[4] Despite the inaccuracies and some disagreement about the beginning of the cycle the belief in the significance of such events generated a stream of publications which grew steadily up to the end of the 16th century. As the great conjunction of 1583 was the last in the watery trigon it was widely supposed to herald apocalyptic changes; a papal bull against divinations was issued in 1586 and as nothing really significant had happened by 1603 with the advent of a new trigon, the public interest rapidly died.

See also

• Triple conjunction

Notes

References

External links

• The Great Conjunction at GeoGebra