Triple conjunction

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