← Encyclopedia of Astrology · lesson 112/235
Exact aspect
An aspect is exact when two planets stand at precisely its angle: 0° apart for a conjunction, 120° for a trine, 90° for a square. Its orb is then zero. As Michael Erlewine puts it, at that moment there are no orbs — the aspect is simply there, at full strength. Before it, the aspect is applying; after it, separating.
Partile and platic
Traditional astrology has two useful words here. An aspect is partile when the two planets are in the same degree of their signs — the Sun at 14°10' Aries and Mars at 14°50' Leo are in partile trine, though 40 minutes of arc apart. Any looser aspect within orb is platic. William Lilly treats partile aspects as markedly stronger, and the distinction is still a handy way to spot the tightest contacts at a glance.
Perfection
In horary and electional astrology, the moment an applying aspect becomes exact is its perfection: the point at which the matter it signifies is said to come about. Lilly's judgements turn on whether an aspect between the significators will perfect, how many degrees it has to travel to do so — which suggests the timing — and whether anything prevents it on the way.
A worked example
At a full moon with the Sun at 15°20' Taurus and the Moon at 15°20' Scorpio, the two lights are in exact opposition. An hour earlier the Moon, moving about half a degree an hour, was some 30' short, and the opposition was applying; an hour later it is 30' past and separating. A transit of Jupiter to a natal Venus works in the same way, only over days or weeks rather than hours.
How readings use it
The exact moment is usually when an aspect is most clearly felt — though not always the moment events happen; with slow planets the whole window around exactness tends to matter. The lists of period transits here give each contact's peak — when it is exact or, if it never quite perfects, when it comes closest — and its orb at that moment. In a birth chart, aspects within about a degree are the ones most astrologers lean on first; where this entry shows the contacts in your own chart, anything within 1° is counted as exact. In the charts here an exact aspect has a strength of 1.