View source for Great conjunction

{{short description|Conjunction of the planets Jupiter and Saturn}}
{{Use dmy dates|date=February 2018}}
[[File:TheGreatConjunction2020.png|thumb|[[Shift-and-add|Stacked]] photograph of the great conjunction of 2020 four hours before closest approach, with [[Jupiter]] 6{{ndash}}7 [[arcminute]]s below [[Saturn]]. The moons [[Io (moon)|Io]], [[Ganymede (moon)|Ganymede]], [[Europa (moon)|Europa]], and [[Titan (moon)|Titan]] are visible.|upright=1.4]]

A '''great conjunction''' is a [[conjunction (astronomy)|conjunction]] of the planets [[Jupiter]] and [[Saturn]], when the two planets appear closest together in the sky. Great conjunctions occur approximately every 20 years when Jupiter "overtakes" Saturn in its [[orbit]]. They are named "great" for being by far the rarest of the conjunctions between [[naked-eye planets]]<ref>{{cite web |last1=Ford |first1=Dominic |title=Great Conjunction |url=https://in-the-sky.org/article.php?term=great_conjunction |website=In The Sky |access-date=22 December 2020 |date=20 October 2020}}</ref> (i.e. excluding [[Uranus]] and [[Neptune]]).

The spacing between the planets varies from conjunction to conjunction with most events being 0.5 to 1.3 [[degree (angle)|degrees]] (30 to 78 [[arcminute]]s, or 1 to 2.5 times the width of a [[full moon]]). Very close conjunctions happen much less frequently (though the maximum of 1.3° is still close by [[inner planet]] standards): separations of less than 10 arcminutes have only happened four times since 1200, most recently in 2020.<ref name="auto3" />

== In history ==
{{See also|Astrological aspect#Great conjunctions}}
Great conjunctions attracted considerable attention in the past as omens. During the late [[Middle Ages]] and [[Renaissance]] they were a topic broached by the pre-scientific and transitional astronomer-astrologers of the period up to the time of [[Tycho Brahe]] and [[Johannes Kepler]], by scholastic thinkers such as [[Roger Bacon]]<ref>'' The Opus Majus'' of Roger Bacon, ed. J. H. Bridges, Oxford: Clarendon Press, 1897, Vol. I, p. 263.</ref> and [[Pierre d'Ailly]],<ref>[http://warburg.sas.ac.uk/pdf/fah1620p.pdf '' De Concordia astronomice Veritatis et narrations historic'' (1414)]</ref> and they are mentioned in popular and literary works by authors such as [[Dante]],<ref name=Woody>{{cite journal|last1=Woody|first1= K. M.|title=Dante and the Doctrine of the Great Conjunctions|journal= Dante Studies, with the Annual Report of the Dante Society|volume= 95 |date=1977|issue= 95|pages=119–134|jstor=40166243}}</ref> [[Lope de Vega]],<ref>[[Frederick A. de Armas]], “Saturn in Conjunction: From Albumasar to Lope de Vega.” in ''Saturn from Antiquity to the Renaissance'', ed. Massimo Ciavolella and Amilcare A. Iannucci (Toronto: Dovehouse Editions, 1993), pp. 151-72. {{ISBN| 9781895537000}}</ref> and [[Shakespeare]].<ref name=Aston>{{cite journal |last1=Aston |first1=Margaret |title=The Fiery Trigon Conjunction: An Elizabethan Astrological Prediction |journal=Isis |date=1970 |volume=61 |issue=2 |pages=159–187 |doi=10.1086/350618|s2cid=144351963 }}</ref> This interest is traced back in Europe to translations of Arabic texts, especially [[Albumasar]]'s book on conjunctions.<ref>'' De magnis coniunctionibus'' was translated in the 12th century, a modern edition-translation by K. Yamamoto and Ch. Burnett, Leiden, 2000</ref>

Clusterings of several planets were considered even more significant. The Chinese apparently remembered the clustering of all five planets in 1953 BC, and noted the clustering of all but Venus in 1576 BC and of all five in 1059 BC. These were connected in Chinese thought to the founding of the first three historical dynasties, the [[Xia dynasty]], the [[Shang dynasty]], and the [[Zhou dynasty]]. The intervals involved, of 377.8 years (19 great conjunction intervals) and 516.4 years (26 great conjunction intervals) bring Mars back to approximately the same position. Further repeats of the 516-year period lead to the clustering in AD 1524, considered ominous in Europe at the time of the [[Radical Reformation]], and the upcoming clustering of September 2040, which will involve all five planets again, in a longitude span of less than 7°.<ref>{{cite journal |last1=D.W.Pankenier |title=Astrological origins of Chinese dynastic ideology |journal=Vistas in Astronomy |date=1995 |volume=39 |issue=4 |pages=503–516 |doi=10.1016/0083-6656(95)00007-0 |url=https://www.lehigh.edu/~dwp0/Assets/images/astroorigins.pdf}}</ref><ref>September 12, 2040 in {{cite web |title=Ephemerides for Year 2040 |url=https://www.findyourfate.com/astrology/ephemeris/2040.html#september}}</ref>

== Celestial mechanics ==
{{Main|Celestial mechanics}}
[[File:Jupiter-Saturn-1981.png|thumb|400px|Diagram showing the movements of Jupiter and Saturn during the 1980–81 triple conjunction]]
On average, great conjunction seasons occur once every 19.859 [[Julian year (astronomy)|Julian years]] (each of which is 365.25 days). This number can be calculated by the [[synodic period]] formula

:<math>\frac{1}{\left ( \frac{1}{J} - \frac{1}{S} \right )} \approx 7253.46 \; \mathrm{days} \displaystyle,</math>

in which {{Mvar|J}} and {{Mvar|S}} are the [[orbital period]]s of Jupiter (4332.59 days) and Saturn (10759.22 days), respectively.<ref name="auto3">{{Cite web|url=https://sparky.rice.edu/public-night/jupsat2.html|title=Jupiter-Saturn Conjunction Series|website=sparky.rice.edu}}</ref> This is about 52 days less than 20 years, but in practice, Earth's orbit size can cause great conjunctions to reoccur anytime between 18 years 10 months and 20 years 8 months after the previous one. (See table below.) Since the equivalent periods of other naked-eye planet pairs are all under 900 days, this makes great conjunctions the rarest.

Occasionally there is more than one great conjunction in a season, which happens whenever they're close enough to [[opposition (astronomy)|opposition]]: this is called a [[triple conjunction]] (which is not exclusive to great conjunctions). In this scenario, Jupiter and Saturn will occupy the same [[right ascension]] on three occasions or same [[ecliptic longitude]] on three occasions, depending on which definition of "conjunction" one uses (this is due to [[apparent retrograde motion]] and happens within months). The most recent triple conjunction occurred in 1980–81<ref name="auto2">{{Cite web|last=Jones|first=Graham|title=The December 2020 Great Conjunction|url=https://www.timeanddate.com/astronomy/planets/great-conjunction|access-date=2020-12-10|website=timeanddate.com|language=en}}</ref> and the next will be in 2238–39.

The most recent great conjunction occurred on 21 December 2020, and the next will occur on 4 November 2040. During the 2020 great conjunction, the two planets were separated in the sky by 6 [[arcminutes]] at their closest point, which was the closest distance between the two planets since 1623.<ref name="auto1">{{Cite web |last=Hunt |first=Jeffrey L. |date=2020-02-20 |title=1623: The Great Conjunction of Jupiter and Saturn |url=https://whenthecurveslineup.com/2020/02/20/1623-the-great-conjunction-of-jupiter-and-saturn/ |access-date=2020-08-24 |website=When the Curves Line Up |language=en}}</ref> The closeness is the result of the conjunction occurring in the vicinity of one of the two [[ecliptic longitude|longitudes]] where the two orbits appear to intersect when viewed from the Sun (which has a point of view similar to Earth).

{| class=wikitable align=right width=400
|[[File:Jupiter-Saturn-great-conjunctions.png|200px]]<BR>Jupiter and Saturn's great conjunctions repeat every ~120°, Saturn's path relative to Jupiter in blue.
|[[File:Keplers trigon.jpg|200px]]<BR>Kepler's trigon, a diagram of great conjunctions from [[Johannes Kepler]]'s 1606 book ''[[De Stella Nova]]''
|}

Because 19.859 years is equal to 1.674 Jupiter orbits and 0.674 Saturn orbits, three of these periods come close to a whole number of revolutions. As successive great conjunctions occur nearly 120° apart, their appearances form a triangular pattern. In a series, every third conjunction returns after some 60 years to the vicinity of the first. These returns are observed to be shifted by some 8° relative to the fixed stars, so no more than four of them occur in the same [[zodiacal]] constellation. Usually the conjunctions occur in one of the following ''[[Triplicity|triplicities]]'' or ''trigons'' of zodiacal constellations:
#Aries, Sagittarius, and Leo
#Taurus, Capricorn, and Virgo
#Gemini, Aquarius, and Libra
#Cancer, Pisces, and Scorpius
After about 220 years the pattern shifts to the next trigon, and in about 800 or 900 years returns to the first trigon.<ref>If {{mvar|J}} and {{mvar|S}} designate the periods of Jupiter and Saturn then the return takes <math>1/(5/S-2/J).</math> Using sidereal periods, this comes to about 836 years. But the return must be a whole number of conjunction intervals, such as 794, 854, or 913 years. However, for returning to the same [[right ascension]], periods must be used with respect to the [[celestial equinox]], giving about 763 years. See Etz.</ref>

The three points of the triangle revolve in the same direction as the planets at the rate of approximately one-sixth of a revolution per four centuries, thus creating especially close conjunctions on an approximately four-century cycle. Currently the longitudes of close great conjunctions are about 307.4 and 127.4 degrees, in Capricornus and Cancer respectively. 

In astrology, one of the [[Classical element|four elements]] was ascribed to each triangular pattern. Particular importance was accorded to the occurrence of a great conjunction in a new trigon, which is bound to happen after some 240 years at most.<ref name=Etz>Etz D., (2000), [http://adsabs.harvard.edu/full/2000JRASC..94..174E ''Conjunctions of Jupiter and Saturn''], Journal of the Royal Astronomical Society of Canada, Vol. 94, p.174</ref> Even greater importance was attributed to the beginning of a new cycle after all fours trigons had been visited.
Medieval astrologers usually gave 960 years as the duration of the full cycle, perhaps because in some cases it took 240 years to pass from one trigon to the next.<ref name=Etz/> If a cycle is defined by when the conjunctions return to the same [[right ascension]] rather than to the same constellation, then because of [[axial precession]] the cycle is less than 800 years.<ref>See previous footnote.</ref> Use of the [[Alphonsine tables]] apparently led to the use of precessing signs, and [[Kepler]] gave a value of 794 years (40 conjunctions).<ref name=Etz/><ref name="Woody"/>

Despite mathematical errors and some disagreement among astrologers about when [[Triplicity|trigons]] began, belief in the significance of such events generated a stream of publications that grew steadily until the end of the 16th century. As the great conjunction of 1583 was last in the water trigon it was widely supposed to herald apocalyptic changes; a [[papal bull]] against divination was issued in 1586 but as nothing significant happened by the feared event of 1603, public interest rapidly died. By the start of the next trigon, modern scientific consensus had condemned astrology as pseudoscience, and astronomers no longer perceived planetary alignments as omens.<ref name=Thomas>Keith Thomas, ''Religion and the Decline of Magic: Studies in Popular Beliefs in Sixteenth and Seventeenth-Century England'' ([[Oxford University Press]], 1971) p. 414-415, {{ISBN|9780195213607}}</ref> However, in the year 1962, when all five planets formed a cluster 17° wide, there was considerable concern.<ref>{{cite web |title=Planets for dessert |url=https://science.nasa.gov/science-news/science-at-nasa/2000/ast30mar_1m |publisher=NASA Science}}</ref>

[[File:Great conjunction separations.svg|thumb|500px|Cumulative distribution of separation distance of great conjunctions between AD 1200 and AD 2400 (blue), and an approximation formula (red)]]
Saturn's [[orbital inclination|orbit plane]] is inclined 2.485 degrees relative to Earth's, and Jupiter's is inclined 1.303 degrees. The [[ascending node]]s of both planets are similar (100.6 degrees for Jupiter and 113.7 degrees for Saturn), meaning if Saturn is above or below Earth's orbital plane Jupiter usually is too. Because these nodes align so well it would be expected that no closest approach will ever be much worse than the difference between the two inclinations. Indeed, between year 1 and 3000, the maximum conjunction distances were 1.3 degrees in 1306 and 1940. Conjunctions in both years occurred when the planets were tilted most out of the plane: longitude 206 degrees (therefore above the plane) in 1306, and longitude 39 degrees (therefore below the plane) in 1940.<ref name="auto3" />

== List of great conjunctions (1200 to 2400) ==

The following table<ref name="auto3" /> details great conjunctions in between 1200 and 2400. The dates are given for the conjunctions in [[right ascension]] (the dates for conjunctions in ecliptic longitude can differ by several days). Dates before 1582 are in the [[Julian calendar]] while dates after 1582 are in the [[Gregorian calendar]].

[[Ecliptic longitude|Longitude]] is measured counterclockwise from the location of the [[First Point of Aries]] (the location of the March equinox) at epoch [[J2000]]. This non-rotating coordinate system doesn't move with [[axial precession|the precession of Earth's axes]], thus being suited for calculations of the locations of stars. (In [[astrometry]] latitude and longitude are based on the ecliptic which is [[Earth's orbit]] extended sunward and anti-sunward indefinitely.) [[Equatorial coordinate system|The other common conjunction coordinate system]] is measured counterclockwise in [[right ascension]] from the First Point of Aries and is based on Earth's [[celestial equator|equator]] and the [[meridian of longitude|meridian]] of the equinox point both extended upwards indefinitely; ecliptic separations are usually smaller.

Distance is the angular separation between the planets in sixtieths of a degree ([[minutes of arc]]) and [[elongation (astronomy)|elongation]] is the [[angular distance]] from the Sun in degrees. An elongation between around −20 and +20 degrees indicates that the Sun is close enough to the conjunction to make it difficult or impossible to see, sometimes more difficult at some geographic [[latitude]]s and less difficult elsewhere. Note that the exact moment of conjunction cannot be seen everywhere as it is below the horizon or it is daytime in some places, but a place on Earth affects minimum separation less than it would if an [[inner planet]] was involved. Negative elongations indicate the planet is west of the Sun (visible in the morning sky), whereas positive elongations indicate the planet is east of the Sun (visible in the evening sky).

The great conjunction series is roughly analogous to the [[Saros series]] for [[solar eclipse]]s (which are Sun–Moon conjunctions). Conjunctions in a particular series occur about 119.16 years apart. The reason it is every six conjunctions instead of every three is that 119.16 years is closer to a whole number of years than {{sfrac|119.16|2}} = 59.58 is, so Earth will be closer to the same position in its orbit and conjunctions will appear more similar. All series will have progressions where conjunctions gradually shift from only visible before sunrise to visible throughout the night to only visible after sunset and finally back to the morning sky again. The location in the sky of each conjunction in a series should increase in longitude by 16.3 degrees on average, making one full cycle relative to the stars on average once every 2,634 years. If instead we use the convention of measuring longitude eastward from the First Point of Aries, we have to keep in mind that the equinox circulates [[axial precession|once every c. 25,772 years]], so longitudes measured that way increase slightly faster and those numbers become 17.95 degrees and 2,390 years.

A conjunction can be a member of a [[triple conjunction]]. In a triple conjunction, the series does not advance by one each event as the constellation and year is the same or close to it, this is the only time great conjunctions can be less than about 20 years apart.<ref name="auto3" />

{| class="wikitable sortable" style="text-align:right"
! Date !! [[ecliptic longitude|Longitude]]<br />(degrees) !! [[angular distance|Distance]]<br />(arcminutes) !! [[elongation (astronomy)|Elongation]]<br />(degrees) !! Series !! Easy to see !! Triple
|-
| 16 April 1206 || 66.8 || 65.3 || +23.0 || 2 || {{small|Depends on observer latitude}} || No
|-
| 4 March 1226 || 313.8 || 2.1 || −48.6 || 3 || Yes || No
|-
| 21 September 1246 || 209.6 || 62.3 || +13.5 || 4 || No || No
|-
| 23 July 1265 || 79.9 || 57.3 || −58.5 || 5 || Yes || No
|-
| 31 December 1285 || 318.0 || 10.6 || +19.8 || 6 || {{small|Depends on observer latitude}} || No
|-
| 24 December 1305 || 220.4 || 71.5 || −70.0 || 1 || Yes || rowspan=3 | Yes
|-
| 20 April 1306 || 217.8 || 75.5 || +170.7 || 1 || Yes
|-
| 19 July 1306 || 215.7 || 78.6 || +82.5 || 1 || Yes
|-
| 1 June 1325 || 87.2 || 49.2 || −0.4 || 2 || No || No
|-
| 24 March 1345 || 328.2 || 21.2 || −52.5 || 3 || Yes || No
|-
| 25 October 1365 || 226.0 || 72.6 || −3.7 || 4 || No || No
|-
| 8 April 1385 || 94.4 || 43.2 || +58.8 || 5 || Yes || No
|-
| 16 January 1405 || 332.1 || 29.3 || +18.1 || 6 || No || No
|-
| 10 February 1425 || 235.2 || 70.7 || +104.1 || 1 || Yes || rowspan=3 | Yes
|-
| 10 March 1425 || 234.4 || 72.4 || −141.6 || 1 || Yes
|-
| 24 August 1425 || 230.6 || 76.3 || +62.6 || 1 || Yes
|-
| 13 July 1444 || 106.9 || 28.5 || −15.9 || 2 || No || No
|-
| 7 April 1464 || 342.1 || 38.2 || −52.6 || 3 || Yes || No
|-
| 17 November 1484 || 240.2 || 68.3 || −12.3 || 4 || No || No
|-
| 25 May 1504 || 113.4 || 18.7 || +33.5 || 5 || {{small|Depends on observer latitude}} || No
|-
| 30 January 1524 || 345.8 || 46.1 || +19.1 || 6 || No || No
|-
| 17 September 1544 || 245.1 || 69.2 || +53.4 || 1 || Yes || No
|-
| 25 August 1563 || 125.3 || 6.8 || −42.1 || 2 || Yes || No
|-
| 2 May 1583 || 355.9 || 52.9 || −51.2 || 3 || Yes || No
|-
| 17 December 1603 || 253.8 || 59.0 || −17.6 || 4 || No || No
|-
| 17 July 1623 || 131.9 || 5.2 || +12.9 || 5 || No || No
|-
| 24 February 1643 || 0.1 || 59.3 || +18.8 || 6 || No || No
|-
| 17 October 1663 || 254.8 || 59.2 || +48.7 || 1 || Yes || No
|-
| 23 October 1682 || 143.5 || 15.4 || −71.8 || 2 || Yes || rowspan=3 | Yes
|-
| 8 February 1683 || 141.1 || 11.6 || +175.8 || 2 || Yes
|-
| 17 May 1683 || 138.9 || 15.8 || +77.5 || 2 || Yes
|-
| 21 May 1702 || 10.8 || 63.4 || −53.5 || 3 || Yes || No
|-
| 5 January 1723 || 265.1 || 47.7 || −23.8 || 4 || {{small|Depends on observer latitude}} || No
|-
| 30 August 1742 || 150.8 || 27.8 || −10.3 || 5 || No || No
|-
| 18 March 1762 || 15.6 || 69.4 || +14.5 || 6 || No || No
|-
| 5 November 1782 || 271.1 || 44.6 || +44.9 || 1 || Yes || No
|-
| 16 July 1802 || 157.7 || 39.5 || +41.3 || 2 || Yes || No
|-
| 18 June 1821 || 27.1 || 72.9 || −62.9 || 3 || Yes || No
|-
| 26 January 1842 || 281.1 || 32.3 || −27.1 || 4 || {{small|Depends on observer latitude}} || No
|-
| 20 October 1861 || 170.2 || 47.4 || −39.5 || 5 || Yes || No
|-
| 17 April 1881 || 33.0 || 74.5 || +3.8 || 6 || No || No
|-
| 28 November 1901 || 285.4 || 26.5 || +38.3 || 1 || Yes || No
|-
| 8 September 1921 || 177.3 || 58.3 || +11.1 || 2 || No || No
|-
| 6 August 1940 || 45.2 || 71.4 || −89.8 || 3 || Yes || rowspan=3 | Yes
|-
| 21 October 1940 || 41.1 || 74.1 || −165.7 || 3 || Yes
|-
| 14 February 1941 || 39.9 || 77.4 || +73.3 || 3 || Yes
<!--
Source lists this as February 1940, but simulation in Stellarium shows it should be February 1941.
-->
|-
| 18 February 1961 || 295.7 || 13.8 || −34.5 || 4 || {{small|Depends on observer latitude}} || No
|-
| 1 January 1981 || 189.8 || 63.7 || −91.4 || 5 || Yes || rowspan=3 | Yes
|-
| 6 March 1981 || 188.3 || 63.3 || −155.9 || 5 || Yes
|-
| 25 July 1981 || 185.3 || 67.6 || +62.7 || 5 || Yes
|-
| 28 May 2000 || 52.6 || 68.9 || −14.6 || 6 || No || No
|-
| 21 December 2020 || 300.3 || 6.1 || +30.2 || 1 || {{small|Depends on observer latitude}} || No
|-
| 4 November 2040 || 197.8 || 72.8 || −24.6 || 2 || {{small|Depends on observer latitude}} || No
|-
| 8 April 2060 || 59.6 || 67.5 || +41.7 || 3 || Yes || No
|-
| 15 March 2080 || 310.8 || 6.0 || −43.7 || 4 || Yes || No
|-
| 18 September 2100 || 204.1 || 62.5 || +29.5 || 5 || {{small|Depends on observer latitude}} || No
|-
| 15 July 2119 || +73.2 || 57.5 || −37.8 || 6 || Yes || No
|-
| 14 January 2140 || 315.1 || 14.5 || +22.7 || 1 || {{small|Depends on observer latitude}} || No
|-
| 20 February 2159 || 215.3 || 71.2 || −50.3 || 2 || Yes || No
|-
| 28 May 2179 || 80.6 || 49.5 || +16.1 || 3 || No || No
|-
| 8 April 2199 || 325.6 || 25.2 || −50.0 || 4 || Yes || No
|-
| 1 November 2219 || 221.7 || 63.1 || +6.8 || 5 || No || No
|-
| 6 September 2238 || 93.2 || 39.3 || −67.6 || 6 || Yes || rowspan=3 | Yes
|-
| 12 January 2239 || 90.2 || 47.5 || +161.3 || 6 || Yes
|-
| 22 March 2239 || 88.4 || 45.3 || +89.9 || 6 || Yes
|-
| 2 February 2259 || 329.6 || 33.3 || +19.6 || 1 || {{small|Depends on observer latitude}} || No
|-
| 5 February 2279 || 231.9 || 69.9 || −80.3 || 2 || Yes || rowspan=3 | Yes
|-
| 7 May 2279 || 229.9 || 73.8 || −172.6 || 2 || Yes
|-
| 31 August 2279 || 227.2 || 74.9 || +73.3 || 2 || Yes
|-
| 12 July 2298 || 100.6 || 28.3 || −6.0 || 3 || No || No
|-
| 26 April 2318 || 339.8 || 41.8 || −51.8 || 4 || Yes || No
|-
| 1 December 2338 || 237.3 || 66.3 || −7.4 || 5 || No || No
|-
| 22 May 2358 || 107.5 || 18.5 || +50.7 || 6 || Yes || No
|-
| 18 February 2378 || 343.7 || 50.5 || +19.4 || 1 || No || No
|-
| 2 October 2398 || 240.7 || 65.9 || +58.2 || 2 || Yes || No
|}
{{Col-begin}}
{{Col-2}}
{{Bar chart|float=left
| title = Number of events 1200–2400 by closeness
| data_max = 22
| label_type = Angular distance
| data_type = Number of conjunctions
| label1 = 0 to 10 arcmin | data1 = 5
| label2 = 10 to 20 arcmin | data2 = 8
| label3 = 20 to 30 arcmin | data3 = 7
| label4 = 30 to 40 arcmin | data4 = 5
| label5 = 40 to 50 arcmin | data5 = 10
| label6 = 50 to 60 arcmin | data6 = 8
| label7 = 60 to 70 arcmin | data7 = 16
| label8 = 70 to 78.6 arcmin | data8 = 16
| label9 = over 78.6 arcmin | data9 = 0
}}
{{Col-2}}
{{Bar chart|float=left
| title = Number of events 1200–2400 by elongation
| data_max = 22
| label_type = Elongation
| data_type = Number of conjunctions
| label1 = −180 to −135 degrees | data1 = 4
| label2 = −135 to −90 degrees | data2 = 1
| label3 = −90 to −45 degrees | data3 = 15
| label4 = −45 to 0 degrees | data4 = 17
| label5 = 0 to +45 degrees | data5 = 22
| label6 = +45 to +90 degrees | data6 = 12
| label7 = +90 to +135 degrees | data7 = 1
| label8 = +135 to +180 degrees | data8 = 3
}}

{{Bar chart|float=left
| title = Number of events 1200–2400 by triplicity
| data_max = 54
| label_type = Type of set
| data_type = Number of conjunctions
| label1 = Part of a triple conjunction | data1 = 21
| label2 = Single conjunction | data2 = 54
}}
{{Col-end}}
{{clear}}

== Notable great conjunctions ==
{| class="wikitable sortable"
|+ List of close great conjunctions consisting of all events under 9.95 [[arcminutes]] between AD&nbsp;1 and 3000,{{efn|Dates before 1582 are in the [[Julian calendar]] while dates after are in the [[Gregorian calendar]].}} plus other notable events.<ref name="auto1" /><ref name="auto3" />
|-
! Date !! [[Ecliptic coordinates]] ([[J2000|non-rotating/star tracking]]) !! Separation (in arcminutes) !! Visibility<br />{{efn|There is always at least a small area around one or both poles that cannot see due to [[midnight sun]] or midnight twilight; this is not mentioned when the conjunction is easily visible from most of each hemisphere.}} !! Notes
|-
| | 1 March 1793 BC ||153.4°|| 1.3 || Evening || The closest conjunction between [[prehistory|prehistoric times]] and the 46th century AD. Part of triple conjunction.
|-
| | 28 December 424 BC ||322.8°|| 1.5 || Evening, hard to see. || |
|-
| | 6 March 372 ||316.6°|| 1.9 || Morning || The closest conjunction of the first three millennia AD.
|-
| | 31 December 431 ||320.6°|| 6.2 || Evening, hard to see. || |
|-
| | 13 September 709 ||130.8°|| 8.3 || Morning, part of a triple conjunction. || |
|-
| | 22 July 769 ||137.8°|| 4.3 || Too close to the Sun to be visible. || |
|-
| | 11 December 1166 ||303.3°|| 2.1 || Evening, hard to see. || |
|-
| | 4 March 1226 ||313.8°|| 2.1 || Morning || |
|-
| | 25 August 1563 ||125.3°|| 6.8 || Morning || |
|-
| | 16 July 1623 ||131.9°|| 5.2 || Evening, hard to see (especially from Northern Hemisphere). || |
|-
| | 21 December 2020 ||300.3°|| 6.1 || Evening, hard to see from high northern latitudes, not visible in Antarctic (poor angle, [[midnight sun|summer sun]]). || 303+ degree [[heliocentric]] longitude close to the ideal 317 degree [[orbital plane|orbit plane]] intersection longitude for closeness ([[J2000]])
|-
| | 15 March 2080 ||310.8°|| 6.0 || Morning, hard to see from mid and high northern latitudes|| |
|-
| | 24 August 2417 ||119.6°|| 5.4 || Morning, not easy to impossible to see from parts of the Southern Hemisphere [[midnight sun|and Arctic]]. || |
|-
| | 6 July 2477 ||126.2°|| 6.3 || Evening, easier to see in the Southern Hemisphere. || |
|-
| | 25 December 2874 ||297.1°|| 2.3 || Evening, [[midnight sun|summer sun]] hinders viewing in Antarctica. || |
|-
| | 19 March 2934 ||307.6°|| 9.3 || Morning || |
|-
| | 8 March 4523 ||287.8°|| 1.0 || Morning, not easy to see from high northern latitudes and the South Pole area due to a low height above the horizon and/or [[midnight sun]] or "midnight twilight". || The closest conjunction in almost 14,400 years.<ref name="auto3" />

|}

{{Bar chart|float=left
| title = Events closer than 9.95 arcmin AD&nbsp;1–3000, sorted by direction
| data_max = 8
| label_type = Longitude (from Earth)
| data_type = Number of conjunctions
| label1 = 119 to 138 degrees | data1 = 6
| label2 = 297 to 321 degrees | data2 = 8
| label3 = Other | data3 = 0
}}
{{clear}}

=== 7&nbsp;BC ===
[[File:Sky Jerusalem South-7BC-11-12.gif|thumb|A simulated view of the great conjunction of 7&nbsp;BC as viewed from [[Jerusalem]] on the evening of 12 November.|upright=1.4]]
When studying the great conjunction of 1603, [[Johannes Kepler]] thought that the [[Star of Bethlehem]] might have been the occurrence of a great conjunction. He calculated that a triple conjunction of Jupiter and Saturn occurred in 7&nbsp;BC (−6 using [[astronomical year numbering]]);<ref>{{Cite journal |title=Kepler and the Star of Bethlehem
|last=Burke-Gaffney |first=W.
|journal=[[Journal of the Royal Astronomical Society of Canada]] |year=1937 |volume=31 |page=417 |bibcode=1937JRASC..31..417B |url=http://adsabs.harvard.edu/full/1937JRASC..31..417B |access-date=2020-05-27}}</ref><ref>{{Cite book |first=Michael R. |last=Molnar |title=The Star of Bethlehem: The Legacy of the Magi |publisher=[[Rutgers University Press]] |year=1999}}</ref>

=== 1563 ===
The astronomers from the [[Cracow Academy]] ([[Jan Muscenius]], Stanisław Jakobejusz, Nicolaus Schadeck, Petrus Probosczowicze, and others) observed the great conjunction of 1563 to compare [[Alfonsine tables]] (based on a [[geocentric model]]) with the [[Prutenic Tables]] (based on [[Copernican heliocentrism]]). In the [[Prutenic Tables]] the astronomers found Jupiter and Saturn so close to each other that Jupiter covered Saturn<ref name=":0">{{Cite book|last=Kesten|first=Hermann|title=Copernicus and his World|publisher=New York: Roy Publishers|year=1945|pages=320}}</ref> (actual angular separation was 6.8 minutes on 25 August 1563<ref name="auto3" />). The Alfonsine tables suggested that the conjunction should be observed on another day but on the day indicated by the Alfonsine tables the angular separation was a full 141 minutes. The Cracow professors suggested following the more accurate Copernican predictions and between 1578 and 1580 Copernican heliocentrism was lectured on three times by Valentin Fontani.<ref name=":0" />

This conjunction was also observed by [[Tycho Brahe]], who noticed that the Copernican and Ptolemaic tables used to predict the conjunction were inaccurate. This led him to realise that progress in astronomy required systematic, rigorous observation, night after night, using the most accurate instruments obtainable.<ref>{{cite book |last=Håkansson |first=Håkan |title=Att låta själen flyga mellan himlens tinnar |trans-title=Letting the soul fly among the turrets of the sky |publisher=Atlantis |page=45 |location=Stockholm |year=2006 |isbn=978-9173531047}}</ref>

=== 2020 ===

<!-- Do not change capitalization in image name unless you also change it on Wikimedia Commons and every place on Wikipedia where the image is shown (including non-English versions like Hindi Wikipedia) -->

[[File:Jupiter saturn separation 2020 Dec.png|thumb|Separation of Jupiter and Saturn around the time of the 2020 great conjunction]]

The great conjunction of 2020 was the closest since 1623<ref name="auto1" /><ref name="auto3" /> and eighth closest of the first three millennia AD, with a minimum separation between the two planets of 6.1 [[Minute and second of arc|arcminutes]].<ref name="auto3" /> This great conjunction was also the most easily visible close conjunction since 1226 (as the previous close conjunctions in 1563 and 1623 were closer to the Sun and therefore more difficult to see).<ref name="witness">{{cite web|url=https://www.wcia.com/news/witness-the-great-conjunction-of-jupiter-and-saturn-on-december-21st/|title=Witness the Great Conjunction of Jupiter and Saturn on December 21st|author=Jacob Dickey|publisher=WCIA|date=6 December 2020|access-date=20 December 2020}}</ref> It occurred seven weeks after the heliocentric conjunction, when Jupiter and Saturn shared the same heliocentric longitude.<ref>{{Cite web|last=Hunt|first=Jeffrey L.|date=2020-09-11|title=2020, November 2: Jupiter – Saturn Heliocentric Conjunction|url=https://whenthecurveslineup.com/2020/09/11/2020-november-2-jupiter-saturn-heliocentric-conjunction/|access-date=2020-10-29|website=When the Curves Line Up|language=en}}</ref>

The closest separation occurred on 21 December at 18:20 UTC,<ref name="auto2" /> when Jupiter was 0.1° south of Saturn and 30° east of the Sun. This meant both planets appeared together in the field of view of most small- and medium-sized telescopes (though they were distinguishable from each other without optical aid).<ref>{{Cite web |date=2019-12-11 |title=2020: December 21: The Great Conjunction of Jupiter and Saturn |url=https://whenthecurveslineup.com/2019/12/11/2020-december-21-the-great-conjunction-of-jupiter-and-saturn/ |access-date=2020-08-11 |website=When the Curves Line Up |language=en}}</ref> During the closest approach, both planets appeared to be a binary object to the naked eye.<ref name="witness" /> From mid-northern latitudes, the planets were visible one hour after sunset at less than 15° in altitude above the southwestern horizon in the constellation of [[Capricornus]].<ref>{{Cite web |last=Hunt |first=Jeffrey L. |date=2019-12-11 |title=2020: December 21: The Great Conjunction of Jupiter and Saturn |url=https://whenthecurveslineup.com/2019/12/11/2020-december-21-the-great-conjunction-of-jupiter-and-saturn/ |access-date=2020-08-27 |website=When the Curves Line Up |language=en}}</ref><ref>{{Cite web |title=5 upcoming conjunctions visible in the night sky, and how to see them |url=https://www.skyatnightmagazine.com/advice/skills/conjunctions-in-night-sky-how-see/ |access-date=2020-08-17}}</ref>

The conjunction attracted considerable media attention, with news sources calling it the "Christmas Star" due to the proximity of the date of the conjunction to [[Christmas]], and for a great conjunction being one of the [[Star of Bethlehem#Planetary conjunction|hypothesized explanations]] for the biblical [[Star of Bethlehem]].<ref>{{Cite news|url=https://www.theguardian.com/science/2020/dec/14/starwatch-christmas-star-closest-great-conjunction-400-years-jupiter-saturn|title=Starwatch: 'Christmas star' is the closest great conjunction in almost 400 years|first=Stuart|last=Clark|newspaper=The Guardian |date=14 December 2020|via=www.theguardian.com}}</ref>

==== Gallery ====
<gallery mode="packed" heights="150px">

File:Grosse.Konjunktion.P1080051.jpg|Photograph taken two days before closest approach with a separation of approximately 15 arcminutes.
File:Great Conjunction image photographed on December 19, 2020.jpg|Great conjunction photographed on December 19, 2020, with a {{convert|14|in|mm|order=flip|abbr=on}} SCT telescope and color CCD.
File:2020 Great Conjunction simulation by NASA, labeled, 2020-12-21 2215UTC.jpg|Simulated best-case scenario view through a telescope.
File:Saturn—Jupiter—Conjunction.jpg|Photograph of the great conjunction of 2020 taken two days before closest approach with the four [[Galilean moons]] visible around Jupiter. ([[Titan (moon)|Titan]] can also be seen to the right of Saturn.)
File:KoniunkcjaJS.gif|December 21, 2020, Jupiter and Saturn, 130mm Bresser Messier
File:Grande congiunzione Giove Saturno 22 dicembre 2020ok.jpg|Photograph depicting the great conjunction, taken from Syracuse, Italy.
File:Great conjunction.jpg|Photograph of Jupiter and Saturn with the [[Moon]] on 16 December 2020
</gallery>

=== 7541 ===
As well as being a triple conjunction, the great conjunction of 7541 is expected to feature two [[occultation]]s: one partial on 16 February, and one total on 17 June.<ref name="auto2" /> Superimposition requires a separation of less than approximately 0.4 arcminutes. This will be the first occultation between the two planets since 6857 BC, and the only instance of two occultations within the same year in maybe a million years.<ref>{{cite web|url=http://www.solexorb.it/SolexOld/Jusatocc.txt|title=Was an occultation of Saturn by Jupiter ever seen, or will it ever be seen from Earth?|first=Aldo|last=Vitagliano|website=solexorb.it|author-link=Solex (software)|year=2011|archive-url=https://web.archive.org/web/20160722191042/http://www.solexorb.it/SolexOld/Jusatocc.txt|archive-date=22 July 2016|url-status=live}}</ref><ref name="auto3" />

== See also ==
*[[Positional astronomy]]

==Notes==
{{notelist}} 

== References ==
{{Reflist}}

== External links ==
{{commons category multi|Conjunctions of Jupiter - Saturn|Jupiter Saturn conjunction in December 2020}}
* [https://www.geogebra.org/m/dXk8gaNt Orbital Motion Simulation of Jupiter and Saturn] at [[GeoGebra]]
* [https://sparky.rice.edu/public-night/jupsat.html The December 21, 2020 Conjunction of Jupiter and Saturn]
* [https://www.imcce.fr/news/conjonction-exceptionnelle-jupiter-saturne The exceptional conjunction of Jupiter and Saturn on December 21, 2020!] {{in lang|Fr|En}}
* [http://www.astropixels.com/blog/2020/12/great-conjunctions/ Great Conjunctions] {{Webarchive|url=https://web.archive.org/web/20201206211258/http://www.astropixels.com/blog/2020/12/great-conjunctions/ |date=6 December 2020 }}

{{Portal bar|Astronomy|Stars|Spaceflight|Outer space|Solar System}}
{{DEFAULTSORT:Great Conjunction}}
[[Category:Astrometry]]
[[Category:Astrological aspects]]
[[Category:Conjunctions (astronomy and astrology)]]
[[Category:Jupiter]]
[[Category:Saturn]]