Ayanamshas

The sidereal parameter (on position, house, and chart endpoints) and the system parameter (on the ayanamsha endpoint) accept an ayanamsha by name or by Swiss Ephemeris number.

An ayanamsha defines the offset between the tropical and sidereal zodiacs. The most commonly used system is Lahiri (the Indian government standard).

Available systems

Every name here is accepted by a request and returned in the system field of an ayanamsha response, so a value you read can be sent straight back. Names are case-insensitive, and hyphens and underscores are interchangeable. The numbers are Swiss Ephemeris numbers, 0 to 46. Systems marked ★ are anchored to a fixed star rather than to a precession model.

This table is generated from the same catalogue the API parses with, and it is the enum in the OpenAPI document. GET /v1/ayanamsha?system=all returns exactly these entries.

Star-anchored systems

Twelve systems (★ above) fix the zodiac to a star rather than to a precession model: True Citra puts Spica at 0° Libra, True Revati puts ζ Piscium at 29°50′ Pisces, the galactic-centre family puts Sagittarius A* at a chosen longitude, and so on. They need the star's apparent position at the moment in question, so their value varies slightly with the ephemeris used, by a few millionths of a degree. The engine refused them before swephrs v0.20.0 (and, before that, returned tropical positions silently); they compute now, and the test suite holds every one of them to the Swiss Ephemeris's own value.

Renamed systems

Six systems were catalogued under misattributed names. The corrected names are canonical and come back in system; the old spellings still parse.

Example

# By name
?sidereal=lahiri

# By Swiss Ephemeris number
?sidereal=1

# A star-anchored system
?sidereal=true_citra

# Every system at once (ayanamsha endpoint)
/v1/ayanamsha?datetime=2024-03-20T12:00:00Z&system=all