Orb

The margin of allowable variance from an exact aspect angle within which two planets are still considered to be in aspect, typically a few degrees.

An orb is the allowed deviation from the exact angular distance of an aspect. Two planets do not have to be exactly 120 degrees apart for the trine to count — most astrologers treat anything within 6 to 8 degrees of exact as a working trine. The orb is what makes aspect detection practical, because exact aspects are momentary and rare.

The width of the orb depends on the aspect, the planets, and the context. The major aspects (conjunction, opposition, trine, square) get wider orbs than the minor aspects (semi-square, sesquiquadrate, quintile). The luminaries (Sun and Moon) get wider orbs than the inner planets, and the inner planets get wider orbs than the outer planets — although the convention is not uniform across schools.

For transit work, orbs are usually tighter than for natal interpretation. A transit is a moving event, and the felt intensity peaks within a degree or two of exact. ZODIA's transit detection uses planet-specific orbs: 2 degrees for the Moon, 4 degrees for Mercury and Venus, 5 degrees for the Sun, 6 degrees for Mars, and 8 degrees for Jupiter and Saturn. These choices are tuned to surface the activations most users actually feel.

A planet inside the orb of an aspect is said to be "in aspect" or "in orb". A planet outside the orb is said to be "out of orb" or "not in aspect". As planets move, they move into orb, reach exact, and move out of orb — this whole approach-and-separation arc is one of the central rhythms of transit timing.