# Validation Snapshot

Reference run: 2026-07-22, topocentric station A68. The calculation and JPL
Horizons used the same frozen JPL SBDB orbit solution for each object. Where
SBDB supplied a complete fitted/covariance element epoch, propagation starts at
that epoch instead of a convenient top-level osculating epoch.

| Case | Orbit type | Maximum sky difference |
|---|---|---:|
| 433 Eros | ordinary elliptic | below report resolution (0.0000 arcsec) |
| C/2023 A3 | near-parabolic/hyperbolic with A1/A2/A3 | 0.0082 arcsec |
| 2P/Encke | comet with A1/A2/A3 | 0.0031 arcsec |
| 2I/Borisov | interstellar, e=3.356 with A1/A2/A3 | 0.0287 arcsec |
| 99942 Apophis, 2029 encounter | extreme topocentric motion | 0.0822 arcsec |
| 367943 Duende, 2013 encounter | extreme topocentric motion | 0.0670 arcsec |

The complete machine-readable report is included as
`validation/horizons-n16-validation-20260722.json`.

Interpretation:

- All six frozen extreme cases remain below one arcsecond.
- The current official Horizons N16 snapshot improves Apophis from 0.2961 to
  0.0822 arcsec and Duende from 0.1891 to 0.0670 arcsec compared with the
  explicit no-asteroid mode.
- Duende improved from 4.5209 to 0.1891 arcsec by propagating the original JPL
  fit/covariance epoch forward across the encounter instead of propagating a
  post-encounter top-level epoch backward.
- These numbers validate this frozen test set. They are not a promise that a
  different or newer orbit solution will produce the same apparent position.
- MPC legacy ephemeris pages are a separate orbit/source comparison and are
  not used as proof of the numerical integrator.
- The N16 runtime snapshot used for this validation differed from its original
  official Horizons SPKs by at most 7.240 m in the sampled interpolation check.
- The public package does not redistribute that precomputed snapshot. The
  supplied generator lets each user create and verify equivalent local data.
