A triple conjunction is an astronomical event when two planets or a planet and a star appear to meet each other three times during a brief period, either in opposition or at the time of inferior conjunction, if an inferior planet is involved. The visible movement of the planet or the planets in the sky appears therefore normally prograde at the first conjunction, retrograde at the second conjunction, and again prograde at the third conjunction.

The lining-up of three planets is a particular case of syzygy.

There are three possible cases of triple conjunctions.

Between Mercury and Venus

At nearly every superior conjunction of Venus (when Venus passes behind the Sun) there is a triple conjunction between Mercury and Venus. In most cases the second conjunction is not visible, because both planets have too small elongation from the Sun.

Triple conjunctions between Mercury and Venus are also possible when they are passing between Earth and the Sun at the same time. This event is much rarer, and also in this case the second conjunction is usually not observable.

Of inferior planets with superior planets or stars

If Mars is in conjunction with the Sun, there is often a triple conjunction between Mars and Mercury or between Mars and Venus. In the events in which Mercury is involved, the second conjunction is invisible because of small elongation from Sun; both other events are difficult to see because of the nearness to horizon and the relatively low brightness of Mars, which is there always near its greatest distance from Earth, barely visible.

For a Mars–Venus triple conjunction all three events can almost always be seen, but Mars is dim because of its great distance from the Earth.

Triple conjunctions between the inferior planets Mercury and Venus and the superior planets Jupiter, Saturn, Uranus, Neptune, dwarf planet Pluto or with stars take place when these objects are at the same time in conjunction to Sun while Mercury or Venus are at inferior conjunction. Frequently the second conjunction takes place when both bodies are too close to the Sun in order to be seen, while the other conjunctions are easily visible, especially if the other body is Jupiter, Saturn or a bright star.

With the dim planets Uranus, Neptune and dwarf planet Pluto the visibility of such an event is difficult, because of the low elongation from Sun.

Triple conjunctions of Mercury and Venus with the exterior planets Jupiter, Saturn, Uranus, Neptune, and dwarf planet Pluto happen relatively frequently (approximately once in 10 years).

Between two exterior planets

These are the most interesting triple conjunctions, because all three conjunctions can be seen very easily, because of the great elongation of the planets or stars involved.

Triple conjunctions between the bright exterior planets are very rare: the last triple conjunctions between Mars and Jupiter occurred in 1789–1790, in 1836–1837 and in 1979–1980. The next events of this kind will be again in 2123 and in 2169–2170.

The last triple conjunctions between Mars and Saturn took place in 1779, 1877 (only in right ascension) and in 1945–1946. The next triple conjunction between these planets will occur in 2148–2149, in 2185 and in 2187.

For both at triple conjunctions between Mars and Jupiter and for triple conjunctions between Mars and Saturn it is possible that two such events follow at an interval of only 2 years. This last happened for Mars and Jupiter in 927 and 929 and will be again in 2742 and 2744. It last happened for Mars and Saturn in 1742–1743 and 1744–1745 and will occur again in 2185 and 2187.

Conjunctions between Jupiter and Saturn—so-called great conjunctions, and are sometimes triple (seven times between AD 1200 and 2400). The three conjunctions occur several months apart, over a broad range of elongations from the sun. The most historically important triple conjunction was that one between Jupiter and Saturn in 7 BCE-5 BCE, which has been proposed as the explanation for the star of Bethlehem. Triple conjunctions between Jupiter and Saturn last took place in 1682–1683, 1821 (only in right ascension), 1940–1941 and 1981. It will not occur again until 2238–2239.

There are more frequent triple conjunctions of Jupiter with Uranus or Neptune. They are unspectacular, but offer a good possibility for amateur astronomers to find these dim planets. The last triple conjunction between Jupiter and Uranus was in 2010–2011 and the next will be in 2037–2038. The last between Jupiter and Neptune was in 2009 and the next will be in 2047–2048.

At each opposition, because of the visible loop movement of the planets, there are triple conjunctions between the planet and some stars. Triple conjunctions between planets and bright stars close to the zodiac are not so frequent (approximately 2 events in 10 years).

Of the planets Mars, Jupiter, Saturn, Uranus, and Neptune in right ascension between 1800 and 2100

Year Involved planets 1st Conjunction 2nd Conjunction 3rd Conjunction
1821 Uranus–Neptune March 17 May 7 December 2
1821 Jupiter–Saturn June 25 November 23 December 23
1836/37 Mars–Jupiter November 14, 1836 March 5, 1837 March 23, 1837
1843 Jupiter–Neptune April 9 September 15 November 5
1845 Mars–Neptune June 18 September 2 October 3
1846 Saturn–Neptune March 31 September 14 December 3
1851/52 Saturn–Uranus July 15, 1851 October 4, 1851 March 4, 1852
1877 Mars–Saturn July 27 August 26 November 4
1888 Mars–Uranus January 9 May 5 June 7
1896/97 Mars–Neptune September 24, 1896 December 12, 1896 February 19, 1897
1896/97 Saturn–Uranus December 28, 1896 June 19, 1897 August 26, 1897
1907 Mars–Uranus May 2 July 19 August 24
1919/20 Jupiter–Neptune September 23, 1919 March 13, 1920 April 20, 1920
1927/28 Jupiter–Uranus July 9, 1927 August 19, 1927 January 23, 1928
1932/33 Mars–Neptune December 5, 1932 March 11, 1933 May 16, 1933
1940/41 Jupiter–Saturn August 15, 1940 October 12, 1940 February 20, 1941
1943/44 Mars–Uranus September 9, 1943 December 26, 1943 January 20, 1944
1945/46 Mars–Saturn October 26, 1945 January 22, 1946 March 19, 1946
1952/53 Saturn–Neptune November 18, 1952 May 31, 1953 July 11, 1953
1954/55 Jupiter–Uranus October 8, 1954 January 6, 1955 May 10, 1955
1964/65 Mars–Uranus December 5, 1964 April 3, 1965 May 6, 1965
1968/69 Jupiter–Uranus December 9, 1968 March 15, 1969 July 18, 1969
1971 Jupiter–Neptune February 2 May 20 September 18
1979/80 Mars–Jupiter December 13, 1979 March 2, 1980 May 4, 1980
1981 Jupiter–Saturn January 14 February 19 July 30
1983 Jupiter–Uranus February 17 May 16 September 24
1988 Saturn–Uranus February 13 June 27 October 18
1989 Saturn–Neptune March 3 June 24 November 12
1993 Uranus–Neptune January 26 September 17 September 28
2009 Jupiter–Neptune May 25 July 13 December 20
2010/11 Jupiter–Uranus June 6, 2010 September 22, 2010 January 2, 2011
2025/26 Saturn–Neptune June 29, 2025 August 6, 2025 February 16, 2026
2037/38 Jupiter–Uranus September 8, 2037 February 19, 2038 March 30, 2038
2041/42 Mars–Uranus November 2, 2041 March 16, 2042 March 18, 2042
2047/48 Jupiter–Neptune July 24, 2047 November 15, 2047 February 26, 2048
2063 Mars–Uranus February 23 May 27 July 17
2066 Jupiter–Uranus January 19 June 27 August 18
2071/72 Mars–Neptune October 8, 2071 February 5, 2072 February 29, 2072
2079 Saturn–Uranus February 28 August 29 October 23
2085/86 Jupiter–Neptune October 30, 2085 January 13, 2086 June 8, 2086
2088/89 Mars–Neptune December 14, 2088 January 4, 2089 May 13, 2089
2093 Jupiter–Uranus May 16 October 27 November 30

Of the planets Mars, Jupiter, Saturn, Uranus, and Neptune in ecliptic longitude between 1800 and 2100

Year Involved planets 1st Conjunction 2nd Conjunction 3rd Conjunction
1821 Uranus–Neptune March 22 May 3 December 3
1836/37 Mars–Jupiter November 15, 1836 February 28, 1837 March 29, 1837
1843 Jupiter–Neptune April 9 September 12 November 8
1845 Mars–Neptune June 21 August 22 October 8
1846 Saturn–Neptune April 4 September 5 December 11
1888 Mars–Uranus January 11 May 4 June 5
1896/97 Mars–Neptune September 24, 1896 December 13, 1896 February 18, 1897
1897 Saturn–Uranus January 6 June 1 September 9
1907 Mars–Uranus May 2 July 17 August 26
1919/20 Jupiter–Neptune September 24, 1919 March 8, 1920 April 24, 1920
1927/28 Jupiter–Uranus July 15, 1927 August 11, 1927 January 25, 1928
1932/33 Mars–Neptune December 6, 1932 March 7, 1933 May 17, 1933
1940/41 Jupiter–Saturn August 8, 1940 October 20, 1940 February 15, 1941
1943/44 Mars–Uranus September 9, 1943 December 30, 1943 January 16, 1944
1945/46 Mars–Saturn October 27, 1945 January 20, 1946 March 20, 1946
1952/53 Saturn–Neptune November 21, 1952 May 17, 1953 July 22, 1953
1954/55 Jupiter–Uranus October 7, 1954 January 7, 1955 May 10, 1955
1964/65 Mars–Uranus December 6, 1964 March 29, 1965 May 8, 1965
1968/69 Jupiter–Uranus December 11, 1968 March 11, 1969 July 20, 1969
1971 Jupiter–Neptune February 1 May 22 September 16
1979/80 Mars–Jupiter December 16, 1979 February 27, 1980 May 5, 1980
1980/81 Jupiter–Saturn December 31, 1980 March 4, 1981 July 24, 1981
1983 Jupiter–Uranus February 18 May 14 September 25
1988 Saturn–Uranus February 13 June 26 October 18
1989 Saturn–Neptune March 3 June 24 November 13
1993 Uranus–Neptune February 2 August 19 October 25
2009 Jupiter–Neptune May 27 July 10 December 21
2010/11 Jupiter–Uranus June 8, 2010 September 19, 2010 January 4, 2011
2037/38 Jupiter–Uranus September 8, 2037 February 19, 2038 March 30, 2038
2041/42 Mars–Uranus November 2, 2041 March 5, 2042 March 28, 2042
2047/48 Jupiter–Neptune July 22, 2047 November 16, 2047 February 24, 2048
2063 Mars–Uranus February 24 May 28 July 15
2066 Jupiter–Uranus January 20 June 24 August 21
2071/72 Mars–Neptune October 8, 2071 February 2, 2072 March 3, 2072
2079 Saturn–Uranus February 26 August 31 October 21
2085/86 Jupiter–Neptune November 1, 2085 January 10, 2086 June 10, 2086
2093 Jupiter–Uranus May 17 October 21 December 5

Note that conjunctions in right ascension and ecliptic longitude need not take place on the same date. It is possible that there is a triple conjunction in right ascension, but not in ecliptic longitude and vice versa.

Some triple conjunctions between 2100 and 3000

Year Involved Planets
2123 Mars–Jupiter
2148 Mars–Saturn
2170 Mars–Jupiter
2185 Mars–Saturn
2187 Mars–Saturn
2221 Mars–Saturn
2239 Jupiter–Saturn
2279 Jupiter–Saturn
2313 Mars–Jupiter
2319 Mars–Saturn
2388 Mars–Saturn
2456 Mars–Jupiter
2599 Mars–Jupiter
2626–27 Mars–Saturn
2629 Mars–Saturn
2655/56 Jupiter–Saturn
2663 Mars–Saturn
2699–2700 Mars–Jupiter, Mars–Neptune and Jupiter–Neptune.
2742 Mars–Jupiter
2744 Mars–Jupiter
2761 Mars–Saturn
2791 Mars–Jupiter
2794/95 Jupiter–Saturn
2829/30 Mars–Saturn
2842/43 Mars–Jupiter
2866 Mars–Saturn

See also

References

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