Semisquare

latin: semiquadratus (Kepler nomenclature; not attested in classical Latin astronomical literature)

Definition

A minor aspect of 45 degrees between two planets — equivalent to half of a square (90°/2 = 45°) and to one-eighth of the zodiac circle (360°/8 = 45°). The semisquare belongs to the eighth-harmonic family alongside the square (90°) and sesquiquadrate (135°). Marks places it in the canonical aspect-strength hierarchy after the inconjunct.

In Tradition

Across the modern Western minor-aspect tradition (Holden on Kepler; Marks; Rudhyar on Marc Edmund Jones), the semisquare is read as one of the four Keplerian minor aspects (30°, 45°, 135°, 150°) adopted by most modern astrologers, and as a register of mild friction or small-scale dynamic tension. Rudhyar preserves Marc Edmund Jones's coefficient-of-inexactness scale in which the 45° semisquare boundary closes the 7-degree zone of angular-deviation analysis.

In Practice

Astrologers evaluate semisquares when tight — typically within a 2° orb. Marks places the semisquare in the canonical modern-Western aspect-strength hierarchy ('Consider the conjunction to be the strongest aspect, followed by the opposition, square, trine, sextile, inconjunct and semisquare') and treats it as a compensator for missing harder aspects: 'Semisquares, and to some extent, inconjuncts... may compensate for a lack of squares or oppositions.' Practitioners often examine semisquares in event-chart, accident-chart, and disaster-chart contexts where they appear with greater density. Rudhyar's preservation of Marc Edmund Jones's Pythagorean-Astrology coefficient-of-inexactness framework treats the 45° boundary as the closure-point of the 7-degree-zone scale: '52° is a semisquare also coefficient 7' in the formal angular-deviation analysis. Standard orb is typically 2°; close semisquares to luminaries are weighted more heavily.

Historical Origin

The 45° aspect is attributed to Johannes Kepler; it is not part of the Ptolemaic five and is not recognized in Ptolemy's Tetrabiblos. Holden documents Kepler's introduction of the additional minor aspects (30°, 45°, 135°, 150°) adopted by most modern astrologers. Marc Edmund Jones's unpublished Pythagorean-Astrology course preserved by Rudhyar in *The Astrology of Personality* uses 45° as the zone-boundary of the coefficient-of-inexactness 0-to-7 scale.

Etymology

Origin: Latin. Meaning: Semi-square = 'half-square,' from Latin semi- ('half') + quadratus ('square'). The aspect-name encodes its half-of-square (45° = 90°/2) eighth-harmonic structure..

Further Reading

  • Johannes Kepler, Harmonices Mundi
  • James H. Holden, A History of Horoscopic Astrology
  • Tracy Marks, The Art of Chart Interpretation
  • Dane Rudhyar, The Astrology of Personality