First Point of Aries (Babylonian-Stratum)

Definition

The First Point of Aries is the zero-point of zodiacal longitude — the spot from which a planet's degrees are counted around the full 360° of the ecliptic, the Sun's yearly path. In the Hellenistic tropical convention it is the spring equinox, where the Sun crosses the celestial equator heading north. In the Babylonian sidereal convention the zero-point was instead pinned to a fixed place against the Aries constellation — 10° Aries in System A, 8° Aries in System B — with no awareness that the equinox slowly drifts.

In Tradition

Read at the Babylonian stratum, Rochberg shows the Babylonian first-point was anchored to the stars, not the equinox: System A set it at 10° Aries, System B at 8° Aries, and those anchors held steady throughout — evidence that precession, the equinox's slow drift, went undetected. The Hellenistic Greek tropical convention, from Hipparchus (2nd century BCE) and Ptolemy (2nd century CE), moved the zero-point onto the shifting spring equinox; medieval Arabic and Renaissance Western practice kept that as the modern chart's default "0° Aries."

In Practice

For a historian, or for anyone weighing the sidereal-versus-tropical question, the Babylonian-stratum reading makes one thing clear: the modern split between the two zodiacs traces straight back to the Babylonian and Greek conventions for fixing the zero-point. The Babylonian sidereal first-point sits at a fixed place in the sky — originally near particular stars in the Aries constellation — and the modern Lahiri ayanamsha tracks that same convention with a chosen offset. The Hellenistic tropical first-point, by contrast, drifts westward against the constellations at about 1° every 72 years. In the present epoch, the tropical 0° Aries actually falls within the constellation Pisces — roughly 24° away from the Babylonian sidereal anchor. That gap is what keeps the tropical-sidereal split alive in working astrology today.

Historical Origin

The Babylonian sidereal first-point at 10° Aries (System A) and 8° Aries (System B) is documented in late-Babylonian astronomical procedure texts of the 5th century BCE onward (Rochberg, Heavenly Writing 2004, Ch. 3). The earliest direct horoscope evidence is BM 33186 (410 BCE; Rochberg, Babylonian Horoscopes 1998). The Greek tropical convention is credited to Hipparchus (2nd century BCE) and codified by Ptolemy in Almagest III (2nd century CE).

Further Reading

  • Francesca Rochberg, The Heavenly Writing: Divination, Horoscopy, and Astronomy in Mesopotamian Culture
  • Otto Neugebauer, A History of Ancient Mathematical Astronomy