Autumnal Equinox

Definition

One of two annual moments when the ecliptic crosses the celestial equator and the lengths of day and night are equal. In tropical Western astrology it is fixed at 0° Libra; the Sun ingressing this point marks the seasonal turn to autumn in the northern hemisphere and to spring in the southern hemisphere. As a structural feature of the sky it is the descending intersection-point of the ecliptic and equator, paired with the ascending vernal-equinox point at 0° Aries.

In Tradition

Across the Babylonian, Hellenistic, and Arabic-mediated Western traditions the autumnal equinox is treated as a foundational cardinal-date of the schematic year — the autumn-anchor of the four cardinal solar moments (vernal equinox, summer solstice, autumnal equinox, winter solstice) that organise calendar, seasonal-prediction, and ingress doctrines. Hunger & Pingree document the equinox as one of the very few solar phenomena the Late Babylonian Astronomical Diaries record systematically; Carmen Astrologicum defines the equinoctial-degrees doctrine — 0° Aries and 0° Libra — at which day and night are equal.

In Practice

Astrologers use the autumnal equinox in three ways. First, as the Sun's ingress into Libra: the moment is cast as an ingress chart in mundane practice for forecasting the autumn quarter. Second, as a cardinal cross-quarter timing-anchor for ingress-based predictive systems, paired with the other three cardinal solar moments. Third, as a degree-class anchor: in the Dorothean Arabic tradition the equinoctial degrees (0° Aries and 0° Libra) themselves carry a 'balanced day-and-night' signification — Dorotheus Book II Ch. 2.13 reads the Moon at one of these degrees in a stake as a sterility-signal, the rule depending on the structural symmetry of the equinoctial moment. Modern Western practice typically focuses on the ingress-chart use; horary and electional work check the Sun's distance from the equinoxes and solstices when assessing seasonal context.

Historical Origin

The earliest systematic attestation is the Mesopotamian schematic-year tradition. MUL.APIN II i 14-15 fixes the autumnal equinox in Month VII at the Sun's rising 'within the Scales in the East,' with the equinoctial 3:3 day-night watch-ratio. The 19-year Uruk solstice-equinox scheme records the autumn-equinox date across each year of the cycle from -330 onward. The Hellenistic-Arabic doctrine inherits the equinoctial-degree convention through Dorotheus and ʿUmar al-Tabarī, preserving the Greek ἰσημερινά as Arabic darajāt iʿtidāl al-layl wa-al-nahār.

Etymology

Origin: Latin. Meaning: Equal-night of autumn.

Further Reading

• Hermann Hunger & John Steele, MUL.APIN
• Hermann Hunger & David Pingree, Astral Sciences in Mesopotamia
• Dorotheus of Sidon, Carmen Astrologicum