Great conjunctions and the world-years

On the evening of 21 December 2020, people all over the world went outside to look at the south-western sky after sunset. Jupiter and Saturn were so close together that to the naked eye they almost merged into one bright point — the closest they had appeared since 1623. Astronomers called it the "great conjunction". The name is much older than the telescope: it belongs to the astrologers of Baghdad, who built an entire astrology of history on these meetings.

Why these two

Jupiter takes about twelve years to go round the zodiac, Saturn about twenty-nine and a half. Jupiter, the faster, catches Saturn up roughly every twenty years (19.86 on average). They are the two slowest planets the ancients could see, so their meetings were the slowest regular clock in the sky — the right scale, it seemed, for the lives of dynasties, peoples and laws rather than of individuals.

The idea came from Persia. Ptolemy does not use it. Māshāʾallāh wrote a book on conjunctions, religions and peoples, and Abū Maʿshar (787–886), in the book usually called On the Great Conjunctions, made it the backbone of mundane astrology, the astrology of the world (Mundane astrology).

A walk through the elements

Here is the pattern that fascinated them. Each conjunction falls about 243° further round the zodiac than the one before — a little less than two-thirds of a circle, which is the same as going back about a trine. So three meetings in a row land in three signs roughly a trine apart: signs of the same element.

Because the steps are not quite an exact trine, the meetings drift slowly through each sign, and after about two centuries they slip into the next element. Abū Maʿshar called that slip a mutation, and treated it as the turn of an age. Then there are larger rounds still: a full passage through all four elements takes most of a millennium, the exact figure depending on how one counts. Above those he set the "world-years" of his Book of Thousands, cycles meant to measure history from its beginning.

The series we are living in

Here are the recent meetings, calculated for this course. You can see the element changing.

From 1842 the meetings fell in earth signs for well over a century. The 1980–81 conjunction in Libra was an early glimpse of air; in 2000 the meeting dropped back into Taurus; and in December 2020 it entered Aquarius, opening a run of air conjunctions expected to last about two hundred years.

Many astrologers read this in the language of the elements: from earth — matter, land, industry, possessions — towards air — ideas, networks, communication and exchange. It is an attractive picture, and you can find evidence for it if you look. It is also exactly the kind of picture that is easy to fit to anything. Hold it lightly. A great conjunction describes the weather of an age; what people and nations do in that weather is up to them.

How the old astrologers used it

Abū Maʿshar worked at several scales at once.

• The single conjunction. Cast a chart for the moment Jupiter and Saturn meet, and read it for the next twenty years: its sign, its planets' dignity, the house it falls in for a given city.
• The year. Each year, cast the chart of the Sun's entry into Aries — the spring equinox — and read it alongside the conjunction it falls under (Eclipses were read alongside both).
• The series and the mutation. Use the element of the series, and the moment it changed, for the longer arcs of history.

He made strong claims, including that the conjunctions announce the rise and fall of dynasties and even of religions. Those claims were argued over for centuries. Astrologers who followed Ptolemy preferred to judge the year from eclipses and lunations, and Christian and Muslim writers alike condemned the idea that a meeting of planets could announce a new faith. When the Jupiter–Saturn meeting of 1603 fell in Sagittarius, opening what was then called the "fiery trigon", the astronomer Johannes Kepler wrote about it at length — and was both drawn to it and sceptical of it, which is not a bad place to stand.

Finding it in your own chart

You do not need to be a nation to use a great conjunction. Look up where 0°29′ Aquarius falls in your own birth chart.

1. Which house is it in? That house describes an area of life where, for the twenty years from 2020, the meeting of growth (Jupiter) and structure (Saturn) is said to work — something to build, and to take responsibility for.
2. Does it touch anything? If a planet or angle in your chart sits within a few degrees of 0° Aquarius, or exactly opposite or square to it, that planet is drawn into the theme.
3. Watch it come round. Saturn returns to that degree about every twenty-nine years and Jupiter about every twelve. Their passages over the 2020 point, and over the 2040 point at 18° Libra, are natural moments to check in on whatever began.

This is a long-term picture. It inclines a reading of two decades; it does not tell you what will happen in any of them.

Closing the circle

This part of the course began in Baghdad, with astrologers choosing a moment to found a city. It ends with the same people trying to read the whole of history from the slowest clock in the sky. In between you have met the Moon's mansions, the lots and the Persian periods of life. Not all of it has survived the centuries with equal credit, and the best of these astrologers would not have expected it to. What they left was a method of paying close attention to the sky, and a habit of arguing honestly about how far to trust it.

Next, a different tradition again: draconic charts, which measure the zodiac from the Moon's North Node.