Jyotisha Library
Siddhanta · सिद्धान्त
The computational tradition: how planetary positions are actually derived.
Siddhanta is mathematical astronomy rather than interpretation. It defines the models, epochs and corrections used to derive planetary longitudes, and it is the layer where ayanamsha, sunrise reckoning and time-zone handling are decided. Astravya reports which settings it used on every calculation.
How it works in practice
- Compute mean positions from epoch constants, then apply corrections for true longitude.
- Apply the ayanamsha to convert tropical positions to the sidereal zodiac.
- Fix sunrise, day length and time-zone conventions before any Panchang reckoning.
Strengths
- Everything downstream depends on it; errors here corrupt every reading.
- Positions are checkable against modern ephemerides.
Cautions
- Classical constants drift from observed positions over long spans.
- Different ayanamsha choices shift signs and dashas; always state the setting.
How it differs from other schools
Treatises in this school
Glossary
- Ayanamshaअयनांश
- Offset between the tropical and sidereal zodiacs; Lahiri is Astravya's default.
- Mean longitude
- Uniform-motion position before corrections.
- True longitude
- Corrected position actually used in a chart.
- Ahargana
- Count of days from an epoch, used in classical computation.
- Ephemeris
- Table or engine giving planetary positions over time.
Published rules from the knowledge base
Reviewed and released entries recorded under this school, each with its source and rights basis.
No Siddhanta rules have been published yet. Entries appear here once a reviewer releases them.
Every summary on these pages is Astravya's own wording of a classical principle. Sanskrit verses are not reproduced unless the source wording is out of copyright or licensed, and each published rule records its chapter, verse and rights basis.