Opposition
Opposition: an aspect comparing two positions through a separation of 180° in ecliptic longitude. This is an angular relationship viewed from Earth, not the physical distance between the bodies.
How it is defined
The exact angle and the allowed tolerance, called the orb, are different quantities. Set the criterion before interpreting. A separation in longitude does not mean the bodies touch or align in all three dimensions.
How to read it
In astrological language this is associated with polarity and a search for balance. Its nuance depends on the positions and question, without automatically guaranteeing a favourable or unfavourable outcome.
A concrete example
Geometric example: positions at 10° and 190° have a separation of 180°. In a disagreement, distinguish two apparently incompatible needs and look for a concrete way to negotiate between them.
Explore further
When comparing charts, check the orb and system used. This website’s birth chart provides Sun, Moon and ascendant; this entry explains aspects without adding them to that tool’s results.