What an orb is
An aspect is defined by an exact angular distance: the conjunction is 0°, the trine is 120°, the square is 90°. Planets are rarely at exactly these distances when a chart is cast. An orb is the allowance — the tolerance either side of exact within which an aspect is considered active.
If Mars is at 14° Aries and Saturn is at 21° Aries, they are 7° apart. The conjunction is 0°, so the orb is 7°. Whether this counts as a conjunction depends on the orb you apply. If you use 8° for Mars conjunctions, it qualifies. If you use 5°, it does not.
Orbs are not a fixed truth. They are a judgment call that every tradition and every working astrologer makes. What matters is applying them consistently and understanding what the choice implies.
Why orbs exist
Without orbs, every possible aspect would require planetary contact to within a fraction of a degree to count, which would make aspects extremely rare. With no orb limit at all, every planet would be in every possible aspect to every other planet at some crude level of approximation — the chart would have no hierarchy.
Orbs define the middle ground: some inexactness is still real contact; some distance is too far for the aspect to carry force. The range between a 1° trine and a 7° trine is real — both qualify, but they carry different weight.
Orb ranges in practice
Different traditions handle orbs differently, and being specific matters.
Modern Western practice typically applies orbs by aspect type. Common ranges:
- Conjunction (0°): 6°–8° for the Sun and Moon; 4°–6° for other planets
- Opposition (180°): 6°–8° for lights; 4°–6° for other planets
- Trine (120°): 6°–8° for lights; 4°–6° for others
- Square (90°): 6°–8° for lights; 4°–6° for others
- Sextile (60°): 3°–4° for lights; 2°–3° for others
The Sun and Moon receive wider orbs because they are the most powerful bodies. Modern practice generally gives the lights more latitude than the faster personal planets.
Traditional practice often uses the concept of moieties (from the Latin for "half"): each planet is assigned a sphere of influence (the "orb" in the older sense, now usually called moiety or half-orb), and two planets are in aspect when their combined moieties cover the angular distance between them. Typical moiety values: Sun = 7.5°, Moon = 6°, Venus and Mercury = 3.5°, Mars = 4°, Jupiter = 4.5°, Saturn = 4.5°. Two planets are in aspect when the sum of their half-moieties equals or exceeds the gap between them and the exact aspect. A Sun-Mars square, for example, uses 7.5 + 4 = 11.5° as the total allowed orb.
The moiety system produces variable orbs depending on which planets are involved, not just which aspect. Neither system is definitively correct — both are tools for assigning priority.
Minor aspects (semisquare at 45°, quincunx at 150°, semisextile at 30°) conventionally receive much tighter orbs — typically 1°–3° — because they carry less inherent force than the major five aspects and only earn consideration when they are very close.
The hierarchy of tightness
Orb creates a ranking among aspects. A 1° trine and a 7° trine both qualify as trines, but they are not equal testimony.
A 1° trine between Venus and Jupiter speaks with immediacy and specificity — two planets in near-exact ease. That contact shapes the chart clearly. A 7° trine between the same planets is background harmony, present but ambient. It does not disappear from the reading, but it does not lead it either.
When reading a chart, sort major aspects by orb before interpreting them. The tightest aspects are typically the most personally distinctive and most consistently active in the person's life. Looser aspects are real but secondary.
Applying and separating
Orb also enables one of the most useful interpretive distinctions in the chart: whether an aspect is applying or separating.
An aspect is applying when the faster-moving planet is still closing the distance toward exact — the two planets have not yet reached their closest point. The contact is in the process of forming. In traditional practice, applying aspects carry more interpretive weight, because the dynamic or event they describe is still incoming, still building, not yet resolved.
An aspect is separating when the faster planet has already passed the exact degree and is moving away. The contact is diminishing. The two planetary functions have already reached their peak of interaction; the moment of closest contact is behind them.
To determine this: identify the faster-moving planet (generally, Moon is fastest; Saturn, Jupiter, and the outer planets are slowest). Note whether the faster planet's current degree position is still approaching the exact aspect degree or has passed it.
A 2° applying square carries a sense of pressure still arriving. A 2° separating square reflects pressure already absorbed. The orb is the same; the direction changes the interpretive tone.
Applying orbs to interpretation
Start every aspect reading with the tightest aspects, applying first. These are the most forceful, most specific, and most time-sensitive contacts in the chart. Work outward to wider orbs as secondary testimony.
When an aspect is near the edge of your chosen orb — say, 7.5° in a system that uses 8° — treat it with proportionally less weight. It is present, but it is the quietest version of the contact. Do not give it the same prominence as a 2° aspect of the same type.
The orb is not a door that is either open or closed. It is a dimmer — the closer to exact, the brighter the aspect speaks.