The margin of deviation or inexactness allowed for an aspect to remain valid. For example, for two planets to be in opposition they do not have to be separated by exactly 180 degrees: the aspect is still valid if the angle is 175 degrees or 185 degrees. A platic aspect is one which has a wide orb but is still considered significant enough to include in a horoscope interpretation.
The concept of orbs comes from the idea that planets cast a certain amount of light or a halo into the sky; such that another planet that is a few degrees away from an exact or partile aspect will still be under its influence. A planet will cast an orb on either side of it. In modern astrology, an orb of 10 degrees for the sun would capture an aspect within a 20-degree arc. A half-arc, cast either to the left or the right of a planet, is a moeity, and if a traditional astrologer cites an orb of 15 degrees for the sun, she would probably use the moity of 7.5 degrees in determining its aspects.
Determining the size of the orb used is a matter of interpretation: Psychological Astrology tends to use larger orbs, whereas Horary Astrology tends to work with tighter ones. The orb in a separating aspect in horary astrology would often not be considered in a judgment, because it symbolizes a matter that is "over and finished", regardless of how narrow the orb is. Astrologers use different rules to determine how wide an orb to use, so one’s own experience is probably the best guide.
In general, modern astrologers allow larger orbs for the sun and moon, of perhaps 10-12 degrees on either side; with narrower orbs for the other planets, perhaps 5-7 degrees. The type of aspect also plays a role in deciding the size of its orb: larger orbs are used for the major aspects such as the conjunction and opposition, whereas smaller orbs are used for the minor aspects (generally 1 to 3 degrees).
Some astrologers will ignore an aspect if the planets are out-of-sign or dissociate even though the orb may be very close. For example, the moon at 29 degrees Aries and the sun at 2 degrees Scorpio are opposed with only a 3-degree orb, well within their normal range; but because the signs are not opposite one another in the horoscope, traditional and horary astrologers would probably discount it.
Guidelines for Major Aspects:
|Orbs of the major aspects|
- Aspects (Astrodienst: Brief Introduction to Astrology)
- The Classical Origin & Traditional Use of Aspects (several classical orb tables Deborah Houlding 1995/ 2004)
- Table to show Orbs for Aspectual Contact (Houlding)
- Moiety (Glossary of Terms; Skyscript/ Houlding)
- Considerations about Orb (Noel Tyl 1999)
- Aspects, Orbs & Perfection. From William Lilly's Christian Astrology (1st ed. 1647, including Lilly's table of orbs; Warnock 2002)
Sources and References
- Table from the German psychological astrologer Ernst Ott, Karlsruhe