Western astrology

A technical discipline assembled in Hellenistic Egypt from Babylonian omens, Egyptian decans and Greek mathematics — and reinvented as psychology in the twentieth century.

What it is

The system of celestial interpretation built on a chart of the sky as seen from a particular place at a particular moment — most often the moment of a birth.

Its components:

The planets — traditionally seven (sun, moon, Mercury, Venus, Mars, Jupiter, Saturn), with Uranus, Neptune and Pluto added after their discoveries. Each carries a set of significations.
The signs — the twelve divisions of the zodiac, modifying how a planet expresses itself.
The houses — twelve divisions of the local sky relative to the horizon at the moment in question, governing the area of life involved. Several incompatible house systems exist, which is a live internal dispute.
The aspects — the angular relationships between planets: conjunction, opposition, trine, square, sextile.

A reading is the synthesis of these into a judgement. The technical work is considerable, which is why the popular reduction to sun signs bears so little resemblance to it.

Where it came from

Three streams converge in Hellenistic Egypt in roughly the second to first centuries BCE.

Babylonian celestial omens are the oldest, with a documentary record stretching back well over a millennium — the omen series Enūma Anu Enlil records celestial events and their consequences, originally for the king and the state rather than for individuals.

Egyptian decans contributed a thirty-six-fold division of the sky used for timekeeping.

Greek mathematics and philosophy supplied the geometry to compute positions and the cosmological framework in which influence could make sense.

What emerged was something genuinely new: horoscopic astrology, the chart cast for an individual's birth. That innovation — from omens about kingdoms to a reading of a private life — is the beginning of the tradition still practised.

Ptolemy systematised it in the Tetrabiblos in the second century CE, presenting astrology as a natural science on a par with medicine: fallible, difficult, but legitimate.

The tradition passed to the Islamic world, where it was extended substantially by figures including Abū Maʿshar, and returned to Europe through twelfth-century translations. It flourished through the medieval and early modern periods — court astrologers, medical astrology, and in England the enormously successful practice of William Lilly — and then lost its standing, for the reasons in the astrology–astronomy split.

The modern revival is more recent than most people assume. Astrology returned through the Theosophical movement in the late nineteenth century, largely via Alan Leo, who simplified the technique and shifted its emphasis toward character rather than event prediction — partly for accessibility and partly because he was prosecuted for fortune-telling and had reason to reposition what he was doing. The twentieth century completed the turn: Dane Rudhyar's humanistic astrology, and later Liz Greene's psychological astrology, recast the chart as a map of the psyche rather than a forecast of events, importing Jung wholesale.

How it is practised

A chart is calculated for a date, exact time and place. The astrologer assesses planetary positions by sign and house, the aspect pattern, the ascendant and midheaven, and dignities — whether a planet is in a sign where it is traditionally strong or weak. Timing techniques — transits, progressions, returns — extend the reading forward.

Traditional practice is oriented to concrete judgement; modern psychological practice is oriented to self-understanding. These are different enough that practitioners of each sometimes struggle to recognise the other as the same discipline.

What we can and cannot say

We can say the tradition is technically substantial and historically continuous, with a literature spanning two thousand years and internal disagreements — house systems, tropical versus sidereal, traditional versus modern method — argued with real rigour.

We can say the empirical results are negative, as set out in the evidence, and that no mechanism has been proposed that survives contact with physics. The forces the planets exert on a newborn are vanishingly small; the obstetrician's gravitational influence exceeds Mars's by a wide margin.

We can say the modern psychological turn changed what is being claimed. A chart offered as a mirror for reflection is doing something a chart offered as a forecast is not, and the evidence against the second does not straightforwardly apply to the first — though nor does the first inherit the authority of a two-thousand-year tradition that was mostly making the second kind of claim.

We cannot say what people get from it, and it is clearly not nothing. Millions of people find a chart a useful frame for thinking about themselves, and the discipline of sitting with a description of your own tendencies — including the unflattering ones — is not obviously worthless because the source is arbitrary. Whether that requires the planets is the question the tradition has never had to answer.

What it is

Where it came from

How it is practised

What we can and cannot say

Further reading