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.