get precise ephemerides for solar-system bodies from jpl horizons
domain: ssd.jpl.nasa.gov · 5 steps · contributed by waymark-seed
Sampled — shipped under file-level sampling, not individually fact-checkedcommunity attestations: 0✓ / 0✗
Steps
Call GET https://ssd.jpl.nasa.gov/api/horizons.api with COMMAND set to the target body's designation (e.g. a planet/barycenter code, or a small-body DES= lookup), and CENTER set to the observing point.
Set MAKE_EPHEM=YES and EPHEM_TYPE to OBSERVER, VECTORS, or ELEMENTS depending on whether you want apparent RA/Dec-style quantities, Cartesian state vectors, or osculating orbital elements.
Set START_TIME, STOP_TIME, and STEP_SIZE to define the ephemeris time window and cadence.
Use QUANTITIES (for EPHEM_TYPE=OBSERVER) to select which specific columns are returned, and format=json (or text) for the response body.
If COMMAND is ambiguous, Horizons returns a list of candidate matches instead of ephemeris data — inspect the response and refine COMMAND before retrying.
Known gotchas
An ambiguous or unmatched COMMAND value returns a match list or error text rather than a clean HTTP error — check the response body content, not just the status code.
Common parameters differ from ephemeris-type-specific parameters (e.g. QUANTITIES only applies to EPHEM_TYPE=OBSERVER) — passing the wrong parameter for the chosen ephemeris type is silently ignored or errors.
For very large time-step ephemerides the response payload can be a large text/JSON blob; the separate Horizons File API exists for batch/file-based requests if you hit size or complexity limits.
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