IANA timezone identifiers and chart reproducibility
Why America/Chicago carries more information than a fixed UTC offset for modern and historical chart calculations.
Calculation contract · released 2026-08-18
Definition
An IANA timezone identifier names a versioned sequence of civil-time rules, including historical offset changes and daylight-saving transitions.
Calculation procedure
Resolve the location to a zone identifier, apply the rules from a declared tzdb release at the requested local timestamp, and retain both the identifier and resulting offset.
Required inputs
- Location or explicit zone identifier
- Local civil timestamp
- Pinned IANA tzdb release
Maha convention
Maha treats the zone identifier and tzdb version as calculation inputs; an offset such as −06:00 is retained as an output of that resolution.
Uncertainty and edge cases
Historical local practice can be incompletely documented even when software returns an offset. Older dates therefore require source-quality review.
What this does not establish
A timezone identifier does not prove where an event occurred or which local clock was consulted.
Authoritative references
These sources establish the calculation vocabulary, data product, or transformation convention. They do not establish astrological interpretation.
- Time Zone Database
Internet Assigned Numbers Authority · 2026c
Versioned civil-time-zone identifiers, UTC offsets, daylight-saving transitions, and historical rules for representative locations.
Boundary: The database records civil-time practice and can contain historical uncertainty; it does not supply leap seconds or astronomical time scales.