Sunrise-based day boundary
Why a Pañcāṅga weekday and daylight fraction may differ from the UTC or midnight-to-midnight civil calendar.
Calculation contract · released 2026-08-18
Definition
In Maha’s implemented Pañcāṅga convention, vāra runs from local sunrise to the next sunrise, and daylight subdivisions require an actual sunrise and sunset.
Calculation procedure
Search observer-specific rise/set events around the instant, anchor the current vāra to the opening sunrise, and return null for daylight fractions when the events do not exist.
Required inputs
- Instant
- Observer latitude, longitude, and elevation
- Solar rise/set model
- Refraction and limb convention
Maha convention
Maha uses Astronomy Engine rise/set searches; when no sunrise is found it labels a UTC-weekday fallback as unreliable and leaves Rāhu Kāla undefined.
Uncertainty and edge cases
Refraction, elevation, and terrain can shift observed sunrise, while polar seasons can remove the event altogether.
What this does not establish
A computed day segment is not evidence that events begun within it succeed.
Authoritative references
These sources establish the calculation vocabulary, data product, or transformation convention. They do not establish astrological interpretation.
- Astronomy Engine
Don Cross (cosinekitty) · 2.1.19
Locally computed Sun and Moon positions derived from the VSOP87 and JPL-derived lunar theories, together with rise and set times, at the accuracy stated in the library documentation.
Boundary: Positions are computed in process rather than fetched from an authority, so a fact citing this source carries a digest over the computed values and not over a provider response body. Its accuracy is adequate for calendrical work and is not a substitute for a Horizons query where sub-arcsecond agreement matters.
- WGS 84 geographic 2D coordinate reference system
EPSG Geodetic Parameter Registry · EPSG:4326 (revision 2022-11-29)
The WGS 84 latitude and longitude coordinate reference system and axis/unit definitions used for terrestrial observer locations.
Boundary: EPSG:4326 is horizontal; elevation must separately name its value, unit, reference, and uncertainty.