Orb
The orb is the margin of degrees tolerated around an exact aspect for it to count as active. A perfect trine spans one hundred and twenty degrees; with a six-degree orb it stays valid between one hundred and fourteen and one hundred and twenty-six degrees. The smaller the gap to the exact angle, the stronger the aspect is held to be. The orb allowed varies with the planets involved and the astrological school.
A margin, not a border
An aspect does not switch on abruptly to within one degree. The orb says how far you accept it to stay alive. The Sun and the Moon, being luminous, receive wider orbs; minor aspects, tighter margins. It is a matter of dosage, and each astrologer gradually refines their own from looking at many charts.
The tighter, the more vivid
In your chart, look at which aspects are the tightest: those are often the ones felt the most. A square at half a degree weighs more than a trine at five degrees. The orb gives you a quiet hierarchy, a way of knowing which tensions and which gifts speak loudest in your map.
Sources
- , Horoscope Symbols (1981)
- , Aspects in Astrology (1989)