Orb
How close an aspect needs to be to count - the margin of influence.
An orb is the degree of allowance given when determining if an aspect is active. For example, a conjunction (0°) might be considered valid within an 8° orb, so planets at 2° and 9° of the same sign would still be conjunct. Tighter orbs (smaller numbers) indicate stronger aspects. Different astrologers use different orb standards.
Example
Sun at 15° Aries and Moon at 20° Aries are 5° apart - within most conjunction orbs, making this a valid Sun-Moon conjunction.
Cultural Context
Orb standards vary widely. Traditional astrologers often gave larger orbs to Sun and Moon (8-12°) and smaller orbs to other planets. Modern astrologers typically use tighter orbs (5-8° for conjunctions, 3-6° for other aspects). There's no universal standard — different schools and software use different defaults.
Famous Example
Whether two planets are 'in aspect' can depend entirely on orb choice. A Sun at 1° Leo and Saturn at 10° Scorpio would be a square with a 9° orb — valid for some astrologers, too wide for others. This is why interpretations can vary between readings.
Did You Know?
Applying aspects (planets moving toward exact) are traditionally considered stronger than separating aspects (planets moving apart). A Sun-Moon conjunction with Moon at 15° and Sun at 17° (Moon applying to Sun) is often read as more powerful than the reverse.