Sextile

The sextile is an aspect of sixty degrees, formed when two planets stand a sixth of the circle apart. It is one of the five major, or Ptolemaic, aspects, the ones classical astrology recognised as the strongest, and it is counted among the harmonious or soft aspects, gentler than the trine but of the same easy character. Sixty degrees links signs of compatible elements, fire with air or earth with water, so the planets involved cooperate readily. Traditionally the sextile is read as a relation of opportunity and ease that offers its benefit only if it is taken up, an open door rather than a gift delivered, and so it is held to require some effort to activate. Its permitted orb is usually reckoned smaller than that of the trine or square. These are the interpretive conventions of the astrological tradition for this angular relation between planets.

The five major aspects trace to Claudius Ptolemy's Tetrabiblos, compiled in Alexandria in the second century CE; Book I.13 actually names only four figures by exact degree, opposition, trine, quartile and sextile, treating the conjunction as no aspect at all, and the sextile is the mildest of the four. Hellenistic astrologers such as Vettius Valens, whose Anthology dates to around 175 CE, worked the aspects by whole sign and gave the relation a direction, holding that of two planets in aspect one overcomes the other along a fixed order running against the sequence of the signs, a nuance later Western practice mostly dropped once it settled on degree-based orbs. The roughly six-degree orb generally granted the sextile today is narrower than that usually allowed the trine or square, one more mark of its gentle standing among Ptolemy's five figures.

Sixty degrees is an exact figure, but almost nobody reads it exactly. The sextile is granted an orb, a tolerance either side of the exact angle, and the size of that tolerance is one of the places where astrological schools quietly disagree. Traditional practice assigned orbs to the planets rather than to the aspects, so a sextile from the Sun carried a wider working range than a sextile from Mercury, simply because the Sun was held to have a larger sphere of influence. Most modern practice reversed this and assigns the orb to the aspect instead, which produces a narrower and more uniform tolerance for the sextile than for the conjunction or the opposition. Neither convention is derived from anything measurable, and a chart read under one can show a sextile that the other does not.

There is a second and older distinction. In sign-based aspect doctrine, which governs Hellenistic and much traditional practice, two planets are in sextile when they occupy signs sixty degrees apart, whatever their exact degrees. A planet at the first degree of Aries and a planet at the twenty ninth degree of Gemini are in sextile by sign and nowhere near it by degree. Degree-based reading, which is what most contemporary software draws, would show no aspect at all. The sextile suffers more from this than the square or the trine because its reputation is already marginal.

That reputation is the third thing worth knowing. Ancient sources treat the sextile as the weaker relative of the trine, effective but requiring something from the person before it does anything. The distinction survives in the modern habit of calling it an aspect of opportunity rather than of gift.

The sextile belongs to the Hellenistic aspect doctrine codified by Ptolemy, its geometry deriving from the sixfold division of the circle, and its glyph is a six-rayed star or asterisk, the mark following the six equal arcs of the hexagon the aspect inscribes. Unlike the trine and square, the sextile's sign was given a dedicated place in the Unicode Standard rather than being left to a borrowed geometric character: it appears as SEXTILE at U+26B9 in the Miscellaneous Symbols block. The mark is attested together with the rest of the aspect set, conjunction, opposition, square and trine, in the medieval Byzantine codices that preserve Hellenistic Greek horoscopes, and it reached its familiar asterisk-like printed form as astronomical tables and ephemerides were standardised for type in the Renaissance, a later typographic fixing distinct from, and considerably later than, the ancient concept the mark records.

Among the five classical aspects, the sextile shares this purpose-built encoding only with conjunction and opposition; the trine and square instead reuse ordinary geometric shapes drawn from mathematics rather than astrology proper. The choice of a star-like mark rather than the plain hexagon the angle actually inscribes may owe something to the need to distinguish the sign clearly from the six-sided figure itself when both appeared in the same diagram, a practical concern of manuscript and, later, typeset diagram-making rather than a point of astrological doctrine.