Hellenistic astrology

Hellenistic astrology is the form of astrology that took shape in Egypt and the Greek world from about the second century BCE. It combined Babylonian planetary omens, Egyptian decans and the Greek habit of building philosophical systems. Its landmark works are the Anthologiae of Vettius Valens, the Tetrabiblos of Ptolemy, the Carmen Astrologicum of Dorotheus and the Mathesis of Firmicus Maternus.

The tradition was carried into Arabic, then Latin, and became the basis of European astrology. Most of the early Greek sources were not studied in the West for centuries. Translation projects from the 1990s on, such as Project Hindsight, brought them back into circulation and started the present revival.

Alexandria, roughly 2nd century BCE–5th century CE: Babylonian omen-lore met Egyptian decans and Greek philosophy, and astrology became a systematic technē. Ptolemy's Tetrabiblos gave it natural philosophy; Vettius Valens' Anthology preserved hundreds of worked case charts; Dorotheus codified electional practice.

Much of this was lost to Europe for a millennium — until the 1990s "Project Hindsight" translations recovered the original techniques, igniting today's revival. Modern astrologers rediscovered that their tradition had teeth.

The Hellenistic chart uses the tropical zodiac and the whole-sign house system. The first house is the entire sign that is rising. Planets are judged by their sign, their house and their relation to each other by sign-based aspect.

A central concept is sect, the division of planets and charts into day and night. A day chart, with the Sun above the horizon, favours Jupiter, Saturn and the Sun. A night chart favours the Moon, Venus and Mars. A planet that is of the same sect as the chart is said to behave well.

The system of lots places calculated points derived from three bodies. The Lot of Fortune is measured by the distance from the Sun to the Moon, projected from the Ascendant. Timing techniques include annual profections, where each year of life activates the next house in turn, and zodiacal releasing, which divides life into periods using the lots.

The tradition is a reconstruction in part. Many details, especially of timing techniques, are recovered from fragments, and modern practitioners disagree about how to apply them. What is presented today is a modern interpretation of ancient evidence.

Its zodiac is tropical, so the signs are measured from the equinox. A Hellenistic reading and a Jyotisha reading of the same birth use different positions and should not be mixed.