← Encyclopedia of Astrology · lesson 108/235
Orb
An orb is the distance, in degrees, between an aspect's exact angle and the angle two planets actually make. A trine is exactly 120°; if the Moon and Venus are 116° apart, they make a trine with an orb of 4°. The orb is also the allowance — the widest margin within which an aspect is still counted. deVore defines it as the arc between the point where a wide aspect is first deemed strong enough to operate and the point where it is exact.
Planets are rarely exactly in aspect, so every astrologer has to decide where an aspect begins. The answer has never been settled, and the different traditions are worth knowing.
How traditions set it
- By planet. William Lilly gave each planet its own orb — roughly 17° for the Sun, 12½° for the Moon, 12° for Jupiter, 10° for Saturn, 8° for Venus, 7½° for Mars and 7° for Mercury — and two planets were in aspect when within half of each orb added together (their "moieties"). Saturn and the Sun: 5° + 8½° = 13½°.
- By aspect. Many modern astrologers instead give each aspect a range: 8–10° for conjunctions and oppositions, 6–8° for trines and squares, 4–6° for sextiles, 1–3° for minor aspects, often widened when the Sun or Moon is involved. Stephen Arroyo, for instance, allows about 8–9° for the major aspects when the lights are involved and less otherwise.
- By use. Transits, progressions and directions are usually read with much tighter orbs than a birth chart — often 1–2°, because there the question is when.
How it is set here
In the charts here every body carries an allowance: 8° for the Sun and Moon, 7° for the Ascendant and Midheaven, 6° for the other planets and the lunar nodes, 2.5° for asteroids and minor points. A pair uses the tighter of its two allowances. The minor aspects are then capped further: 2° for the semi-square and sesquiquadrate, 1.5° for the quintile and biquintile. Parallels and contraparallels of declination use 1°. In a transit reading the list of contacts shows, by default, those within 3° at their peak; the threshold can be changed.
Strength
Beside each aspect you may see its strength: how tight the aspect is against its own allowance, from 1 when exact to 0 at the very edge. A 3° trine between the Sun and Moon (allowance 8°) is stronger than a 3° trine between Mercury and Chiron (allowance 2.5°, so 3° would not count at all). Strength is shown for information only; nothing is chosen by it. The ease and tension chart weighs each contact in a similar spirit, counting it more the closer it comes to exact.
Why it matters
The tighter the orb, the more clearly an aspect tends to show — most astrologers agree on that, whatever their tradition. A wide aspect is still there; it simply speaks more softly, and it is worth reading alongside whether it is applying or separating.