Orb

The fuller picture

Start with what an orb is a property of, because this is where the short definition misleads. Modern astrology usually gives an orb to the aspect — a trine gets so many degrees, a sextile fewer. The traditional scheme gives it to the planet: each body carries its own orb of light, brighter bodies casting wider ones, and the moiety is half of that. Two planets are in aspect when their distance from exactness is less than the sum of their two moieties. On the table our engine implements, the Sun has a moiety of 8°30′ and Jupiter 4°30′, so a Sun–Jupiter trine is admitted out to 13°, while Mercury and Mars at 3°30′ each are admitted only to 7°. Same aspect, an allowance nearly twice as wide, decided entirely by which planets are involved.

A moiety and an orb are therefore not the same number, and mixing them up halves or doubles everything downstream. The moiety is the half; the working allowance for a pair is the sum.

The rival scheme is one fixed figure per aspect type, and it's perfectly respectable. iHorary carries both. Planetary moieties are the default, and a practitioner-approved fixed table is the alternative — 8° for a conjunction or opposition, 7° for a trine, 6° for a square, 5° for a sextile — chosen as a whole rather than layered on top of the moieties as a second filter. Which system produced a given chart is recorded with that chart, alongside the house system and the term table, so a reading can be audited later rather than re-derived from a guess.

Now the part this page has to be careful about, because it isn't settled and we shouldn't pretend otherwise. The modern practitioner whose doctrine most of this glossary follows states no orb rule anywhere in his book, and his worked charts pull in both directions at once. One of them rests its entire judgment and its only timing on a trine at 12°06′ and a translation at 11°34′, both wider than the moiety sums for those pairs — take those two aspects away and the chart has no perfection, no timing and no answer. Another opens its whole delineation on a sextile at 4°19′, which is comfortably inside our own moiety table and which our chart service doesn't report at all. So one layer of our own stack is looser than the tradition and another is tighter, and the orb question is ruled case by case rather than by one blanket policy. If you want a single number for a single aspect, nobody in this material will give you one.

Three things get run together and are worth separating. An aspect is in orb when the planets are close enough to count. An aspect perfects when they're joined in degree and minute. An aspect is exact when they share degree, minute and second. And partile is a fourth thing that isn't an orb window at all: it means the two planets share the same degree number in their respective signs. Mars at 15°02′ Aries and Saturn at 16°00′ Cancer are within a degree and not partile; Mars at 15°58′ and Saturn at 15°02′ are both. Our own code uses a one-degree window where it says partile, which is a different test from the degree match and one we've recorded rather than quietly kept.

The last thing to know is that the orb does a second job. It's not only an admission test, it's the quantity read for timing: the degrees of distance between the significators give the number of units, and the sign and house give the unit. That makes the orb the single most load-bearing number on the chart, which is why the disagreements above matter more than they look. And there's one calculation where orbs are deliberately left out altogether — whether a planet is void of course, which asks whether the aspect completes before the planet leaves its sign, not whether the two are close now.