Conjunction

Two planets are exactly a hundred and twenty degrees apart perhaps once in a chart. Everything else is approximate, and the amount of approximation an astrologer will accept is called the orb. There is no agreed figure, there never has been, and the disagreement is not a detail: it decides which aspects appear in a chart at all.

The traditional answer gives the orb to the planet. In Lilly's Christian Astrology of 1647, and in the medieval Arabic-derived material behind it, each planet carries its own radius of influence, its orb, sometimes called its light or its beams. Lilly's figures run to roughly fifteen or seventeen degrees for the Sun, twelve for the Moon, nine or ten for Jupiter and Saturn, and seven or eight for Mercury, Venus and Mars. Two planets are in aspect when the distance between them falls within the sum of their moieties, each moiety being half that planet's orb. The consequence is that an aspect involving the Sun reaches much further than one between Mercury and Venus, and the same angular separation counts as an aspect in one pairing and not in another.

The modern answer gives the orb to the aspect. Twentieth-century practice mostly abandoned moieties and assigned a fixed allowance per figure: something like eight to ten degrees for conjunctions and oppositions, six to eight for trines and squares, four to six for sextiles, and two or less for anything minor. Which planets are involved becomes at most a modifier, usually a widening for the Sun and Moon.

Neither scheme is derived from anything. Both are conventions, and the numbers vary from author to author within each. Astrological software makes this invisible by shipping a default orb table and drawing the aspect lines accordingly, so two astrologers looking at the same chart in two programs are looking at different charts. Where a reading here depends on an aspect being present, it is worth knowing that the aspect's existence is a setting.

An aspect within orb is either closing or opening. If the faster planet is still moving toward exactness, the aspect is applying; once it has passed, the aspect is separating. Traditional astrology treats these as different things rather than as two phases of one thing.

An applying aspect is held to promise: the matter is coming, the perfection has not happened yet, the outcome is still in play. A separating aspect describes something already done and now dispersing. In horary practice, where a question is answered from the chart of the moment it was asked, this is the mechanism the judgement runs on, an applying aspect between the significators says yes, a separating one says the matter is past or will not come together. Bonatti and Lilly both build their rules of perfection and prohibition on it, and it carries more weight in their work than the nature of the aspect does.

Modern natal astrology largely dropped the distinction. A square is a square, and whether it is applying or separating rarely changes the delineation. The traditional revival has been pushing back on this since the 1990s and treats the loss as a real one rather than a simplification, on the argument that an aspect which has already perfected is describing something spent.

The complication is retrogradation. A planet turning retrograde can apply to an aspect, separate from it, and apply again, so the same configuration perfects three times. Traditional sources have specific readings for this; modern natal practice mostly does not, which is a further consequence of having stopped tracking the direction of travel.

The conjunction is fundamental to the aspect doctrine set out in the Hellenistic tradition and given its lasting theoretical shape by Ptolemy in the second century. Aspect thinking of this kind was not his invention; Dorotheus of Sidon, whose Carmen Astrologicum is usually dated to the first century, already worked with the same angular relationships, so the doctrine Ptolemy systematised had been circulating among Greek astrologers for some generations before he wrote it down.

In chart work the conjunction is written with a small circle carrying a short radial arm or hook, a mark attested alongside the other planetary and aspect signs in the medieval Byzantine codices that preserve so many ancient Greek horoscopes, and later regularised into its familiar printed form as astronomical and astrological tables began to be typeset in the Renaissance. The symbol was given a dedicated place in digital type comparatively early: it appears in the Unicode Standard as CONJUNCTION, U+260C, in the Miscellaneous Symbols block, present since the standard's first release in 1993, one of only a handful of aspect glyphs to receive their own codepoint rather than being built from letters or borrowed geometric shapes.