Meridian

Definition

The great circle on the celestial sphere that passes through the observer's zenith, the celestial poles, and the nadir. It runs due north–south and is perpendicular to the celestial equator. Where the ecliptic crosses the meridian above the observer (in the northern hemisphere, due south) is the Midheaven; where it crosses below is the Imum Coeli. The meridian does not move with the observer through the day — it stays fixed relative to the place — but it does move with the observer between places.

In Tradition

Across Hellenistic and modern Western tradition, the meridian is paired with the horizon as the two great circles whose intersections with the ecliptic produce the four angles of the chart. Where the horizon supplies the Ascendant–Descendant axis, the meridian supplies the MC–IC axis; together they form the structural skeleton of quadrant-based house systems.

In Practice

Astrologers locate the meridian through the Midheaven (the point of the ecliptic culminating at the upper meridian) and the Imum Coeli (the lower meridian). Planets near the upper meridian are at upper culmination — most visible, most public — and acquire the topical force of the 10th-house cusp. Planets near the lower meridian are at lower culmination — most private, most rooted — and acquire the 4th-house topical force. The MC is also the reference for primary directions, solar arcs, and astrocartography MC-lines; the meridian itself defines the local sidereal time used to compute Placidus, Koch, Regiomontanus, and Campanus cusps.

Historical Origin

Babylonian astronomy used the ziqpu stars (kakkabū ša ziqpi, 'stars that stand upright') as meridian reference markers — Tablet I iv of MUL.APIN lists fourteen canonical ziqpu constellations whose meridian transits timed the night's observations. The Greek tradition codifies the horizon–meridian framework as the basis of horoscopic astrology by Ptolemy's time. Crane reconstructs the meridian as a foundational coordinate reference inherited from the earliest mathematical astronomy.

Etymology

Origin: Latin. Meaning: Of midday.

Further Reading

• Joseph Crane, Astrological Roots: The Hellenistic Legacy
• Hermann Hunger & John Steele, MUL.APIN
• Claudius Ptolemy, Almagest