History & development
Western sidereal astrology is a modern Western tradition associated with zodiac calibrations such as Fagan–Bradley. Its defining computational decision is where the twelve equal signs begin relative to a stellar reference. It should not be collapsed into Indian astrology simply because both can use sidereal coordinates.
Mythology & symbolic world
The familiar twelve sign images remain available, but their coordinates are referred to a different origin. The astronomical constellations occupy unequal areas of sky; twelve equal sidereal signs are a symbolic grid rather than those boundaries.
Provenance: where the rules come from
Record the named ayanamsha, date, precession treatment and ephemeris. Swiss Ephemeris documents many calibrations and cautions that a conventionally 'fixed' zodiac is not perfectly inertial over long periods.
How it is calculated
Choices that change the result: Fagan–Bradley and other ayanamshas; equal signs are not IAU constellations.
Inspect your calculated data →Uses & use cases
- Compare the same birth chart under tropical and Fagan–Bradley coordinates.
- Study how reference-frame choices affect sign labels and return times.
Interpretation methods
Controlled comparison
Change only the zodiac calibration first. Keep bodies and aspect tolerances constant, then compare interpretations from identified tropical and sidereal authors.
Subtracting the same angular offset from two longitudes preserves their mutual separation. A changed sign does not mean their aspect disappeared.
Explore these reading approaches
Concepts in this tradition
Follow a term for its definition, word origin, evidence and connected ideas.
Disagreements & limits
Sources & evidence
Practitioner sources describe their own systems. Historical and astronomical sources support different kinds of claims. Reading exercises are editorial teaching examples.
- Swiss Ephemeris: sidereal astrology and ayanamshas ↗first-party technical documentation