A Great Conjunction is a conjunction of the planets Jupiter

Jupiter

Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...

 and Saturn

Saturn

Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.Saturn,...

. 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.

Greatest conjunction

Greatest conjunction is a conjunction of Jupiter and Saturn at or near their opposition to the Sun

Sun

The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

. In this scenario, Jupiter and Saturn will occupy the same position in right ascension

Right ascension

Right ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:...

 on three separate occasions over a period of a few months.

The so-called "Star of Bethlehem

Star of Bethlehem

In Christian tradition, the Star of Bethlehem, also called the Christmas Star, revealed the birth of Jesus to the magi, or "wise men", and later led them to Bethlehem. The star appears in the nativity story of the Gospel of Matthew, where magi "from the east" are inspired by the star to travel to...

" — thought to have appeared c. 7 BC

7 BC

Year 7 BC was a common year starting on Saturday or Sunday of the Julian calendar and a common year starting on Thursday of the Proleptic Julian calendar...

 — was theorized to be a greatest conjunction; and some went so far as to assert that it was an occultation

Occultation

An occultation is an event that occurs when one object is hidden by another object that passes between it and the observer. The word is used in astronomy . It can also refer to any situation wherein an object in the foreground blocks from view an object in the background...

 of Saturn by Jupiter, with the two planets appearing to merge into a single object as seen from Earth

Earth

Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

. However such an event did not take place at historic times. At the greatest conjunction in 7 BC, which is said to be the "Star of Bethlehem", the minimum distance between Jupiter and Saturn was around 1 degree, this is twice the Moon

Moon

The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

'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.

Great Conjunctions in Right ascension between 1800 and 2100

Date	Time UTC	Planet	Angle distance	Planet	Elongation to sun
July 21, 1802	03:22:00	Jupiter	42' south of	Saturn	37.9° East
June 25, 1821	00:05:09	Jupiter	1°15' north of	Saturn	67.5° West
November 22, 1821	23:49:55	Jupiter	1°20' north of	Saturn	140.2° East
December 23, 1821	09:28:49	Jupiter	1°22' north of	Saturn	108.5° East
January 25, 1842	22:22:31	Jupiter	32' south of	Saturn	26.8° West
October 25, 1861	15:11:20	Jupiter	52' south of	Saturn	43.1° West
April 22, 1881	11:58:20	Jupiter	1°18' north of	Uranus	1.0° East
November 28, 1901	06:10:38	Jupiter	27' south of	Saturn	38.6° East
September 14, 1921	16:22:08	Jupiter	1°02' south of	Saturn	6.2° East
August 15, 1940	13:18:42	Jupiter	1°15' north of	Saturn	97.5° West
October 11, 1940	23:17:26	Jupiter	1°17' north of	Saturn	155.0° West
February 20, 1941	19:14:02	Jupiter	1°21' north of	Saturn	67.7° East
February 18, 1961	14:42:37	Jupiter	14' south of	Saturn	34.6° West
January 14, 1981	07:58:37	Jupiter	1°09' south of	Saturn	103.9° West
February 19, 1981	07:12:10	Jupiter	1°09' south of	Saturn	141.2° West
July 30, 1981	21:32:22	Jupiter	1°12' south of	Saturn	57.9° East
May 31, 2000	10:13:27	Jupiter	1°11' north of	Saturn	16.9° West
December 21, 2020	13:48:52	Jupiter	6' south of	Saturn	30.3° East
November 5, 2040	13:19:46	Jupiter	1°14' south of	Saturn	24.8° West
April 10, 2060	09:01:25	Jupiter	1°09' north of	Saturn	39.8° East
March 15, 2080	08:29:24	Jupiter	6' north of	Saturn	43.8° West
September 24, 2100	01:40:38	Jupiter	1°18' south of	Saturn	25.1° East

Great Conjunctions in ecliptical longitude between 1800 and 2100

Date	Time UTC	Planet	Angle distance	Planet	Elongation to sun
July 17, 1802	22:57:00	Jupiter	39' south of	Saturn	40.6° East
June 19, 1821	16:56:57	Jupiter	1°10' north of	Saturn	63.3° West
January 26, 1842	06:16:53	Jupiter	32' south of	Saturn	27.1° West
October 21, 1861	12:27:02	Jupiter	48' south of	Saturn	39.7° West
April 18, 1881	13:35:59	Jupiter	1°13' north of	Saturn	3.1° East
November 28, 1901	16:37:33	Jupiter	26' south of	Saturn	38.2° East
September 10, 1921	04:13:03	Jupiter	57' south of	Saturn	9.7° East
August 8, 1940	01:13:20	Jupiter	1°11' north of	Saturn	90.9° West
October 20, 1940	04:42:14	Jupiter	1°14' north of	Saturn	164.0° West
February 15, 1941	06:36:25	Jupiter	1°17' north of	Saturn	72.9° East
February 19, 1961	00:07:18	Jupiter	14' south of	Saturn	34.9° West
December 31, 1980	21:17:24	Jupiter	1°03' south of	Saturn	90.9° West
March 4, 1981	19:14:36	Jupiter	1°03' south of	Saturn	155.9° West
July 24, 1981	04:13:35	Jupiter	1°06' south of	Saturn	63.8° East
May 28, 2000	15:56:27	Jupiter	1°09' north of	Saturn	14.9° West
December 21, 2020	18:37:31	Jupiter	6' south of	Saturn	30.1° East
October 31, 2040	12:02:47	Jupiter	1°08' south of	Saturn	20.8° West
April 7, 2060	22:36:24	Jupiter	1°07' north of	Saturn	41.9° East
March 15, 2080	01:49:55	Jupiter	6' north of	Saturn	43.5° West
September 18, 2100	22:50:40	Jupiter	1°13' south of	Saturn	29.4° East

Great Conjunctions and History

Great conjunctions are less spectacular than eclipses or comets but nevertheless they have also attracted considerable attention as celestial omens. During the late Middle age

Middle age

Middle age is the period of age beyond young adulthood but before the onset of old age. Various attempts have been made to define this age, which is around the third quarter of the average life span of human beings....

 and the Renaissance

Renaissance

The Renaissance was a cultural movement that spanned roughly the 14th to the 17th century, beginning in Italy in the Late Middle Ages and later spreading to the rest of Europe. The term is also used more loosely to refer to the historical era, but since the changes of the Renaissance were not...

 they became a rather popular topic broached by most
astronomers of the period up to the times of Tycho Brahe

Tycho Brahe

Tycho Brahe , born Tyge Ottesen Brahe, was a Danish nobleman known for his accurate and comprehensive astronomical and planetary observations...

 and
Kepler, by scholastic thinkers as Roger Bacon

Roger Bacon

Roger Bacon, O.F.M. , also known as Doctor Mirabilis , was an English philosopher and Franciscan friar who placed considerable emphasis on the study of nature through empirical methods...

 The Opus Majus of Roger Bacon, ed. J. H. Bridges, Oxford:Clarendon Press, 1897, Vol. I, p. 263. or Pierre d'Ailly

Pierre d'Ailly

Pierre d'Ailly was a French theologian, astrologer, and cardinal of the Roman Catholic Church....

, and they are mentioned in popular and literary writing by authors such as Dante

DANTE

Delivery of Advanced Network Technology to Europe is a not-for-profit organisation that plans, builds and operates the international networks that interconnect the various national research and education networks in Europe and surrounding regions...

  or Shakespeare. This interest is traced back in Europe to the translations from Arabian sources, most notably Albumasar's book on conjunction.

As successive great conjunction 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
sign astrologers have ascribed one the series of four elements

Classical element

Many philosophies and worldviews have a set of classical elements believed to reflect the simplest essential parts and principles of which anything consists or upon which the constitution and fundamental powers of anything are based. Most frequently, classical elements refer to ancient beliefs...

 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. Even greater importance was attributed to the beginning of on new cycle after all fours trigons had been visited, something which happens in about 800 years.

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. 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 c. As the great conjunction of 1583 was the last in the watery trigon it was widely supposed to herald apocalyptic changes; a papal bull

Papal bull

A Papal bull is a particular type of letters patent or charter issued by a Pope of the Catholic Church. It is named after the bulla that was appended to the end in order to authenticate it....

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.