Planetary
The great conjunction
A great conjunction is the meeting of the two slowest naked-eye planets, Jupiter and Saturn, in the same line of sight. It recurs every 7,253.45 days, about 19.86 years, the time Jupiter needs to lap the slower Saturn once around the Sun. The last fell in December 2020, when the two planets closed to about a tenth of a degree; the next comes in 2040.
This page is about the period itself: the 19.86-year beat, why each meeting lands about 117 degrees further around the zodiac, and why three of them nearly close a triangle that holds for two centuries before drifting on. For the full list of dated meetings, past and future, see the Jupiter-Saturn conjunctions page; to place this cycle beside its siblings, see the cycles index.
On this page
The next Jupiter-Saturn great conjunction is October 31, 2040, in Virgo. They last met in December 2020; great conjunctions recur every 7,253.45 days (19.86 years).
Each meeting falls about 117 degrees further west, so the pair works around the whole zodiac in roughly 800 years.
Where we are in the great conjunction right now
The next great conjunction of Jupiter and Saturn falls on October 31, 2040. With JavaScript on, this panel shows how far Jupiter has gained on Saturn since 2020 and counts down to the next meeting.
Computed live in your browser from the open-source Astronomy Engine; nothing is sent anywhere. See every cycle together on the cosmic clock.
The great conjunction at a glance
| Period | 7,253.45 days (19.86 years) |
|---|---|
| Bodies | Jupiter and Saturn |
| What it is | the synodic period: Jupiter laps the slower Saturn |
| Orbital relationship | 5:2 near-commensurability (not a resonance) |
| Shift each cycle | about 117 degrees west around the zodiac |
| Trigon | meetings cluster in one triangle of signs for about two centuries |
| Longitude return | about 800 years |
| Last conjunction | December 2020 |
| Next conjunction | 2040 |
Sources: U.S. Naval Observatory, Astronomical Applications.
The great conjunction in every unit
Broken into other units and into other cycles, the 7,253.45-day beat reads like this.
| In days | 7,253.45 days |
|---|---|
| In years | 19.859 tropical years (about 19 years 314 days) |
| In hours | about 174,083 hours |
| Jupiter orbits | 1.674 (7,253.45 d / 4,332.6 d) |
| Saturn orbits | 0.674 (7,253.45 d / 10,758.7 d) |
| 5:2 near-commensurability | 5 Jupiter orbits (59.31 yr) about 2 Saturn orbits (58.91 yr) |
| Shift per conjunction | about 117 degrees west; three nearly close a 360 degree triangle |
| Trigon return | about 800 years to the same longitude |
Jupiter's period is 11.862 years and Saturn's is 29.457 years (USNO; Meeus, Astronomical Algorithms). The orbit counts are means; real intervals vary by up to a few months because both orbits are elliptical and each planet speeds up near perihelion.
What the great conjunction is and how it arises
Jupiter orbits the Sun once every 11.862 years and Saturn once every 29.457 years. Because Jupiter is faster, it steadily gains on Saturn, and every so often it draws level, catching Saturn on the same side of the Sun so the two appear close together in our sky. The interval between one catch-up and the next is the synodic period, and for these two planets it works out to 19.86 years.
The meetings do not happen at the same place in the zodiac. Between one conjunction and the next, Saturn has crept about 243 degrees along its orbit, so the new meeting occurs roughly 117 degrees to the west of the last. Three conjunctions, spread over about 60 years, therefore trace a large triangle across the sky, nearly but not quite closing on themselves. The triangle drifts by a small amount each time, so for roughly two centuries the meetings stay within one group of signs, a pattern older astronomers called a trigon.
That slow drift is what carries the cycle across the whole zodiac. It takes about 800 years for the meetings to work all the way around and return near the same longitude. Underlying all of it is a near-commensurability: five Jupiter orbits take almost exactly as long as two Saturn orbits, a 5:2 ratio that is close to whole numbers but is not locked by gravity into a true resonance.
The math
The synodic period follows from the two orbital periods. The rate at which Jupiter gains a full lap on Saturn is the difference of their orbital rates: 1/T = 1/11.862 - 1/29.457 per year. That is 0.084303 minus 0.033948, or 0.050355 laps per year, so T = 19.86 years, which is 7,253.45 days.
The westward shift comes from where Saturn sits when the next meeting arrives. In one synodic period Saturn travels 19.86/29.457 of its orbit, about 0.674 of a turn, or roughly 243 degrees eastward. Measured the short way, that puts each conjunction about 117 degrees west of the one before. Three of them add up to about 351 degrees, nine degrees short of a full circle, which is why the triangle of meeting points slowly rotates rather than standing still.
Those are mean figures. Both orbits are ellipses, so the true gap between conjunctions swings by a few months either side of 19.86 years depending on where each planet is on its path. To see the actual dated meetings and how close the planets came each time, open the Jupiter-Saturn conjunctions page.
The next great conjunctions
| Date | Constellation | Zodiac longitude |
|---|---|---|
| Oct 31, 2040 | Virgo | Libra 17° |
| Apr 7, 2060 | Taurus | Gemini 0° |
| Mar 15, 2080 | Capricornus | Aquarius 11° |
| Sep 18, 2100 | Virgo | Libra 25° |
How the great conjunction relates to other cycles
The great conjunction belongs to a small family of cycles that draw slowly turning figures in the zodiac. The Venus pentagram is its close cousin: where Jupiter and Saturn sketch a rotating triangle, Venus and Earth sketch a five-pointed star, and both arise from ratios of orbital periods that fall near, but not exactly on, whole numbers. Both are near-commensurabilities, not resonances.
The longitudes these meetings are measured against are fixed by the sidereal year, the Sun's return to the same star. And the reason Jupiter and Saturn move so slowly in the first place is the subject of Kepler's three laws: the farther a planet orbits, the longer it takes, which is what makes their meetings so rare.
Frequently asked questions
How often do Jupiter and Saturn meet in a great conjunction?
On average every 7,253.45 days, about 19.86 years. That is the synodic period of the two planets, the time it takes faster Jupiter to gain a full lap on slower Saturn and draw level with it again. The real interval varies by a few months because both orbits are elliptical, but 19.86 years is the mean.
When was the last great conjunction, and when is the next?
The last great conjunction was in December 2020, when Jupiter and Saturn passed about a tenth of a degree apart, close enough to look almost like a single star. The next comes in 2040, one synodic period of about 19.86 years later. For the full list of past and future dates, see the Jupiter-Saturn conjunctions page.
Why do great conjunctions form a triangle in the zodiac?
Each conjunction falls about 117 degrees west of the one before, because that is where Saturn has moved to by the time Jupiter catches it again. Three meetings, spread over about 60 years, therefore land near the three corners of a triangle. The triangle drifts a little each cycle, so the meetings stay in one group of signs for roughly two centuries before moving on.
Is the Jupiter-Saturn 5:2 relationship a resonance?
No. Five Jupiter orbits take almost the same time as two Saturn orbits, a 5:2 ratio, but the match is only approximate and the planets are not held in step by their mutual gravity. That makes it a near-commensurability rather than a true orbital resonance. Real resonances, like Neptune and Pluto's 3:2, are actively maintained and keep the bodies from colliding.
How long until great conjunctions return to the same part of the sky?
About 800 years. Each meeting sits roughly 117 degrees from the last, and three of them fall about nine degrees short of a full circle, so the triangle of meeting points slowly rotates around the zodiac. It takes on the order of eight centuries for the meetings to work all the way around and return near the same longitude they started from.
When is the next great conjunction?
The next great conjunction of Jupiter and Saturn is October 31, 2040. They meet every 19.86 years; the previous one was in December 2020 and the one after next is around 2060.
Keep exploring
- Jupiter-Saturn conjunctions: every dated meeting, past and future
- All cycles by length: see it beside its siblings
- The Venus pentagram: another figure drawn in the zodiac
- The sidereal year: the frame these longitudes are measured against
- Kepler's three laws: why the outer planets move so slowly