What Is an Orb in Astrology? Exact Aspects and Allowed Deviation
How to measure deviation from 60°, 90°, 120° and 180° aspects without confusing the chosen tolerance with an astronomical fact.
The two numbers behind an aspect label
The target angle defines an aspect type; the orb is the allowed deviation from that angle under a chosen astrological rule. If two objects have a circular separation of 93°, they are 3° away from an exact square of 90°. A system permitting a square with an orb of at least 3° includes that pair; a system permitting only 2° does not.
An orb is a convention for categorizing aspects, not an instrumental measurement uncertainty in the telescope. The ecliptic longitude may be known very precisely while two interpreters choose different accepted orb limits. Consequently two websites can agree on the sky and still disagree on whether a loose aspect should be displayed.
Worked examples at sign boundaries
Suppose one point is at 358° and another at 88°. Their difference is 270°, so the smaller circular separation is 360° − 270° = 90°: an exact square. If the second point instead is 91°, the smaller separation is 93°, and the square's deviation is 3°. The location of the 0° zodiac boundary creates no special exception.
The same arithmetic works for sextiles, trines and oppositions. For a conjunction near the beginning of the zodiac, positions 359° and 2° are 3° apart rather than 357°. Always evaluate the shortest circular distance; taking an unadjusted subtraction can mislabel aspects near the 0°/360° wrap.
Compare tools by disclosing their rules
Before concluding that one program is wrong, check whether both use the same planets, ecliptic reference, aspect list and orb widths. Some traditions vary the orb by planet or by aspect type; others use one constant cutoff. A result should say which policy produced the classification, especially for near-boundary cases.
Use the Galaxiora horoscope section to explore the calculations it currently supports, and the connected aspects guide for the five major angles. This explanation does not imply that every historical aspect system or every birth-chart configuration is already certified in the product.
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Sources and methodology
References for checking the astronomical and calendrical facts in this guide. Traditional interpretations are not astronomical measurements.