The Great Conjunctions
Each line joins one meeting of Jupiter and Saturn to the next, from March 1226 to December 2020, on a zodiac wheel. Three meetings in a row make a triangle, and each triangle sits a little further round than the last. The colour of each line is the element of the sign the meeting fell in, so you can watch the triangle move from air to water to fire to earth and back to air.
| Average gap | 19.86 years |
|---|---|
| Each step around the zodiac | About 243°, or 117° back |
| One turn through the elements | About 795 years |
| Present air era began | 21 Dec 2020, 0° Aquarius |
What you are looking at
Jupiter and Saturn, the two slowest planets the eye can see, line up in the sky about every twenty years. Each dot is one of those meetings, placed at its exact degree of the tropical zodiac, with 0 degrees Aries on the left and the signs running counterclockwise as on a birth chart. Each line runs from one meeting to the next.
A meeting falls about two thirds of the way round the zodiac from the one before, so three meetings land roughly a third of the circle apart, nearly always in signs of one element: fire, earth, air or water. The fourth meeting lands a little past the first corner, so the triangle creeps slowly forward through the signs, from fire to earth to air to water, in the order of the zodiac. The lines leave an empty circle in the middle about half the width of the wheel.
At the defaults the picture starts at the meeting of 12 March 1226, at 2 degrees Aquarius, and ends at the one of 21 December 2020, at 0 degrees Aquarius: 40 steps later the meeting is back within about 2.5 degrees of where it began. In between the triangle settles into water from 1425, fire from 1663 and earth from 1842, with a few meetings slipping back and forth at each changeover. Astrologers call these changes the great mutations, and the tradition reads the 2020 meeting as the start of an air era, after a first air meeting in Libra in 1980 and 1981.
The math
Jupiter goes round the Sun in 11.86 years and Saturn in 29.46, so Jupiter catches up with Saturn every 19.86 years on average. In that time Saturn has moved about 243 degrees further along, which is the same as 117 degrees backwards, a third of a circle minus a few degrees. Three steps come back to about 9 degrees past the start, so the corners of the triangle walk slowly forward through the zodiac.
Five orbits of Jupiter take 59.3 years and two of Saturn take 58.9, which is why the pattern so nearly closes. A full turn through all four elements took about 795 years from the air meeting of 1226 to the air meeting of 2020, so each element holds the triangle for about 200 years on average: here 199 years in air, 239 in water, 178 in fire and 179 in earth, longer or shorter depending on where the two planets are on their oval orbits. Within a settled era the triangle keeps to one element for seven to nine meetings in a row.
The gaps themselves vary from about 18.8 to 20.6 years for the same reason. In 1595 Johannes Kepler drew this figure and noticed that the empty circle in the middle is about half the size of the outer one, close to the ratio of Jupiter's orbit to Saturn's (about 0.55). That hunch grew into his first book, the Mysterium Cosmographicum of 1596.
How it is computed
Every meeting is found from real positions (the astronomy-engine library, VSOP87 theory, agreeing with the Swiss Ephemeris to well under an arcminute). First the cheap search: the moments Jupiter and Saturn share a heliocentric longitude, one every 19.86 years. Then, around each one, the moments their apparent positions seen from the Earth match, in the tropical zodiac of that date, refined to about a minute. The frame of date matters here: over 800 years the equinoxes shift by about 11 degrees, which is the difference between one sign and the next.
Some meetings are triple. When the two planets meet near opposition to the Sun they are both looping backwards, and Jupiter passes Saturn three times in under a year. Between 1226 and 2020 that happened five times: in 1306, 1425, 1682 and 1683, 1940 and 1941, and 1980 and 1981. The rule here: passes less than 400 days apart count as one conjunction, placed at the middle pass. So the 1980 and 1981 triple, with passes on 31 December 1980, 4 March 1981 and 24 July 1981, is drawn once, at 4 March 1981, and marked with a ring. The 2020 meeting at 0 degrees Aquarius on 21 December matches the published date. Dates before 1582 are given in the Gregorian calendar extended backwards, as astronomy software counts them, so the meeting of 12 March 1226 fell on 5 March in the Julian calendar used at the time.
Questions
What is a great conjunction?
A meeting of Jupiter and Saturn in the sky, when the two share the same zodiac longitude. It happens about every 20 years. The most recent was on 21 December 2020 at 0 degrees Aquarius, when the two planets were about a tenth of a degree apart and looked almost like one bright star in the evening twilight.
Why do the meetings make a triangle?
Each meeting falls about 243 degrees round the zodiac from the one before, roughly two thirds of a circle. Three of those steps come back almost to the start, so the meetings sit near the corners of a triangle, about 120 degrees apart, usually in signs of the same element.
What is a triple conjunction?
When the meeting happens near the time Jupiter and Saturn are opposite the Sun, both are in retrograde, so Jupiter passes Saturn, falls back past it, and passes it again: three meetings within a year. Here a triple counts as one conjunction, drawn at its middle pass and marked with a ring.
What does the air era mean in astrology?
Astrologers group the conjunctions by the element of their sign and read a change of element, a great mutation, as the turn of a long era. The tradition links the earth era from 1842 with material and industrial growth, and reads the air era that began with the 2020 meeting in Aquarius as one of ideas, networks and communication. That is the tradition's reading, not something the sky can confirm.