great·est e·lon·ga·tion
/ˈɡreɪ.tɪst iːˌlɒŋˈɡeɪ.ʃən/
The maximum angular distance that Mercury or Venus can achieve from the Sun, measured along the ecliptic. Because these planets orbit closer to the Sun than Earth does, they are never seen far from it in the sky.
During the Medieval period, greatest elongation (Latin elongatio maxima) became a standard astronomical and astrological term derived from Arabic and Latin translations of classical works such as Ptolemy’s Almagest and Tetrabiblos. It marks the point at which Mercury or Venus appears farthest from the Sun, determining their visibility as morning stars (eastern elongation) or evening stars (western elongation). Astrologers used these positions to assess a planet’s strength, brightness, and sect condition. For example, a planet at greatest elongation and visible above the horizon was considered free from the Sun’s beams and therefore more capable of expressing its nature clearly. The concept bridged astronomical observation and astrological interpretation, providing a key indicator of planetary potency and phase in the Medieval cosmological model.