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 planetPluto 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.