Angle and History

The biquintile derives, like the quintile, from the fivefold division of the circle at the centre of Kepler's harmonic scheme, published in the Harmonices Mundi of 1619, where the two aspects appear together as products of the same reasoning, that the pentagon's constructibility with compass and straightedge, and its correspondence to a consonant musical interval, made a hundred and forty-four degrees as legitimate an aspect angle as any of the four Ptolemy had already recognised. It has no settled glyph in the way the sextile or the sesqui-quadrate do; it is written with the letters BQ, or with a mark derived from the quintile sign, and it was not among the aspects given a dedicated codepoint when astrological symbols were added to the Unicode Standard, so its appearance still varies between astrology programs and publishers rather than following one fixed convention.

The pentagon and pentagram that the fivefold family carries with it have made the quintile and biquintile a natural pairing in harmonic astrology ever since Kepler first proposed them, and the two aspects are still generally discussed together in modern textbooks rather than treated as separate topics, much as the semi-square and sesqui-quadrate are usually presented as one eightfold pair rather than two unrelated angles.