Reference · Astronomy
What is an orb in astrology?
Kevin Blaxton — software builder; astrology student for 40+ years · figures computed by the OrbHeaven engine
Published · Last revised
An orb is how far an aspect is from exact. Two planets are almost never at precisely an aspect’s exact angle, so an aspect is counted when it falls within an allowed distance of exact, called the orb. The distance from exact is calculated; how wide an orb to allow is an astrological convention.
What is an orb?
Two parts, kept separate. The offset is the exact, measurable gap between the real separation of two planets and the aspect’s exact angle — if a square is 90° and two planets are 94° apart, the offset is 4°. The orb is the allowance: the largest offset still counted as that aspect. Within the orb, the aspect is recognised; beyond it, it is not.
The offset is arithmetic (the degrees don’t lie); the orb is a chosen tolerance laid on top of it.
OrbHeaven’s orbs, and the dial
OrbHeaven’s birth charts allow a set orb per aspect, with a degree more when the Sun or Moon is involved. Transits to your chart use tighter orbs, so the dates describe what is genuinely close. The dial below classifies any separation against these same engine values — set the angle, toggle a luminary, and watch an aspect fall in or out of orb.
- Conjunction (0°) & opposition (180°)
- 8° in a birth chart (9° with the Sun or Moon); 3° for a transit.
- Square (90°) & trine (120°)
- 7° in a birth chart (8° with a luminary); 3° for a transit.
- Sextile (60°)
- 5° in a birth chart (6° with a luminary); 2° for a transit.
- Quincunx (150°)
- 2.5° in a birth chart (3.5° with a luminary); 1.5° for a transit — the tightest, and the most disputed aspect.
Aspect dial
Set the angle · see the aspect- Result
- square — within orb (7° allowed)
Try: set 92° — a square, within its 7° orb; nudge to 98° and it falls out. Tick the luminary box to widen every orb by 1°. Classified live by OrbHeaven’s engine (ASPECT_ANGLES + NATAL_ORBS).
An orb is a convention, not a measurement
There is no independently established, scientific orb. Nothing in astronomy says an aspect “switches on” at 7° and off at 8°; the allowance is a choice within astrological practice, and a reasonable one varies by astrologer, by purpose, and by tradition. Tighter aspects are usually given more weight — itself a convention, not a measured fact.
Where this is disputed
Different astrologers and different software will count an aspect another leaves out, purely because they chose a wider or narrower orb. OrbHeaven states its values so the arithmetic is reproducible; it does not claim they are the correct ones, only the ones it uses.
A short history: orbs of planets, not aspects
Older practice did not give an orb to each aspect at all. In the traditional “moiety” system each planet carried its own orb — a bright planet like the Sun a wide one, a faint one a narrower one — and the orb allowed between two planets was half the sum of their two orbs. The modern habit of a fixed orb per aspect, which OrbHeaven uses, is a later simplification.
Both are conventions; neither is more astronomically “true”. OrbHeaven uses per-aspect orbs because they are transparent and easy to state, and says so.
Common misconceptions
- Is the orb a property of the planets or the sky?
- No. The separation between planets is real and measured; the orb — how much of a gap still counts — is a chosen tolerance from astrological practice, not a natural threshold.
- Why does one app show an aspect another doesn’t?
- Almost always because they use different orbs. The separation is the same; one allowance is wider than the other.
- Why do the Sun and Moon get a wider orb?
- It is a traditional convention — the luminaries are treated as more prominent — not a measured effect. OrbHeaven adds 1° when the Sun or Moon is involved.
References & further reading
- [1] Ptolemy, Tetrabiblos (c. 150 CE) — the classical treatment of the aspects orbs derive from.
- [2] Holden, J. H., A History of Horoscopic Astrology (2nd ed.) — orbs and the traditional moiety system.
- [3] Meeus, J., Astronomical Algorithms, 2nd ed. (Willmann-Bell, 1998) — angular separation, from which the offset is computed.
Suggested citation
Blaxton, K. (2026). What is an orb in astrology. OrbHeaven Reference. https://orbheaven.com/reference/orbsRevision history
- First build. Reuses the engine-backed aspect dial (ASPECT_ANGLES + NATAL_ORBS + the luminary rule) as the interactive orb demonstration; the orb table matches the engine. States plainly that orbs are a convention of practice, not a scientific threshold, and gives the traditional moiety history. No photo. Links Aspects and Degrees.
Related glossary entries
About a minute. Birth time optional, and no account until after you have seen it.
More in the reference library
What is an aspect in astrology? The angles, the orbs, and the geometry
An aspect is the angle between two points in a chart. This is the geometry — the six angles astrologers use, what an orb is, and where the set comes from — with an interactive dial that classifies any separation using OrbHeaven’s engine.
What do the degrees in a birth chart mean?
Every position in a chart is an angle. This explains the 360° circle, the twelve 30° signs, how a sign-and-degree equals an absolute ecliptic longitude, and how degrees drive aspects — keeping the arithmetic separate from interpretation.
Why do planets seem to move backwards? Apparent retrograde motion
Planets never reverse. Retrograde motion is an illusion of perspective as Earth overtakes them — explained with orbital geometry, a worked example from our engine, and the history from Ptolemy to Kepler.