Ephemeris Version and Reproducibility: A Source-Reviewed Guide
A planet label without those dependencies is not a reproducible calculation. Scope and limits are explicit.
Overview
Planetary output names the ephemeris family, data-file or kernel version, calculation library, flags, reference frame, time scale, observer model, and precision. The page shows exactly what to verify, how to repeat the method, where a plausible near miss fails, which variants change the result, and what the evidence cannot establish.
At a glance
- Direct scope
- Reviewed finding — An ephemeris is a versioned numerical data product with a model, reference frame, coverage, constants, interpolation, and precision. A planet label without those dependencies is not a reproducible calculation.
- Evidence to verify
- Method checkpoint — Pin engine and data-file versions, record checksum and coverage, declare geocentric or topocentric apparent options, retain unrounded output, and verify a small fixture set against an independent public ephemeris.
- Repeatable method
- Worked-case result — Two services calculate Mars for the same TT instant. The comparison aligns frame and apparent-position flags, displays full-precision longitude, and locates any residual difference before sign rounding.
- Worked example
- Failure condition — Writing “Swiss Ephemeris” without library version, data files, flags, and fallback mode is insufficient. An engine may silently switch to a lower-precision analytical model outside file coverage.
- Near miss
- Documented variant — A product may choose a validated analytical ephemeris for offline speed or JPL data for research precision. Either can be appropriate when coverage, expected error, and fallback behavior are disclosed.
- Limits and safety
- Use boundary — Ephemeris agreement supports numerical provenance, not astrological efficacy. Software upgrades can change boundary placements, so stored reports should retain their original version rather than being silently rewritten.
Definition and Scope
Planetary output names the ephemeris family, data-file or kernel version, calculation library, flags, reference frame, time scale, observer model, and precision.
An ephemeris is a versioned numerical data product with a model, reference frame, coverage, constants, interpolation, and precision. A planet label without those dependencies is not a reproducible calculation.
Evidence and Repeatable Method
Pin engine and data-file versions, record checksum and coverage, declare geocentric or topocentric apparent options, retain unrounded output, and verify a small fixture set against an independent public ephemeris.
Worked Example and Near Miss
Two services calculate Mars for the same TT instant. The comparison aligns frame and apparent-position flags, displays full-precision longitude, and locates any residual difference before sign rounding.
Writing “Swiss Ephemeris” without library version, data files, flags, and fallback mode is insufficient. An engine may silently switch to a lower-precision analytical model outside file coverage.
Variants and Disagreement
A product may choose a validated analytical ephemeris for offline speed or JPL data for research precision. Either can be appropriate when coverage, expected error, and fallback behavior are disclosed.
Limits and Safe Use
Ephemeris agreement supports numerical provenance, not astrological efficacy. Software upgrades can change boundary placements, so stored reports should retain their original version rather than being silently rewritten.
Sources and editorial basis
- Swiss Ephemeris 2.10 DocumentationSwiss Ephemeris 2.10 manual, chapters 2 “The Ephemerides”, 6 “Sidereal Time, Ascendant, MC, Houses, Vertex”, and 7 “Delta T”, pages 5–64Public technical documentation for ephemerides, time conversions, sidereal time, apparent positions, houses, nodes, and Delta T; software policy and version must still be disclosed.
- NASA JPL Horizons System ManualJPL Horizons Manual sections “General Definitions”, “Coordinate Center (Observing Site) Selection”, “Specification of Time”, “Reference Frames”, “Customizing Output”, and “Definition of Observer Table Quantities”A public astronomy reference for ephemeris quantities, reference frames, time spans, observer locations, and apparent or geometric output choices.