Reference-frame convention · sidereal longitude
Lahiri ayanāṁśa calculations
Lahiri ayanāṁśa is a coordinate conversion convention. Maha Celestial keeps the original tropical longitude and the applied offset so the sidereal result can be audited.
Published 2026-08-18
Calculation chain
Normalize(tropical ecliptic longitude − Lahiri ayanāṁśa) = Lahiri sidereal longitude.
What the ayanāṁśa does
The tropical zodiac is anchored to the moving equinox; a sidereal zodiac is anchored through a chosen stellar reference convention. Precession creates an angular separation between them. An ayanāṁśa supplies the offset used to transform a tropical ecliptic longitude into a sidereal longitude.
What a reproducible record retains
A result is incomplete if it says only “sidereal.” Maha retains the UTC instant, observer location where relevant, tropical longitude, named Lahiri method, numerical offset, normalized sidereal longitude, ephemeris and software version, and precision. Near a sign, nakṣatra, or tithi boundary, the report also marks sensitivity to uncertainty.
- The input instant and historical time-zone resolution
- The tropical longitude before conversion
- The named ayanāṁśa and its value
- The resulting sidereal longitude and boundary distance
- The calculation-library version and precision
Why two sidereal charts may disagree
“Sidereal” is not one universal setting. Different ayanāṁśas place the zero point differently, and small differences can change a placement near a boundary. Node choice, house system, topocentric versus geocentric position, and rounding can introduce further disagreements. A valid comparison must isolate each convention.
Interpretive boundary
Selecting Lahiri defines a coordinate frame. It does not prove that sidereal astrology is empirically valid or superior to another zodiac.