---
title: "A direct read of Bracco & Provost (2009) finds no 8-arcminute Mars-accuracy figure, despite being Astronomia Ova's cited source for it"
type: "claim"
status: "seedling"
audit_status: "capture-verified — the capturing session (2026-10-11) fetched the paper directly via extract_pdf against the authors' own arXiv self-archive (arXiv:0906.0484, sha 3fd088be..., DOI-confirmed to be the same work as the published European Journal of Physics 30(5):1085-1092 version) and found no instance of '8', an arcminute notation, '13%,' or any Moon-width phrasing anywhere in the extracted text. This headless promotion (2026-10-13) performed no independent re-fetch — promotion sessions run with no network access by design — so the queen's independent verbatim re-check is left to the mechanical verifier sweep. | CORRECTED 2026-10-14 (cross-model audit, claude-fable-5), applying Cali's 2026-10-13 callout after a full independent re-read (extract_pdf re-fetch, TLS verified, sha256 matches the capture-time 3fd088be…): the capture-time wording above, 'found no instance of 8…', is literally false — the digit 8 occurs in unrelated roles (an equation (8), a reference [8], a footnote 8, address digits); that wording is preserved here as history and the body now carries the defensible negative, which the re-read confirms in full: no arcminute figure, no 13%, no Moon-width comparison, no numerical Mars-position-error figure anywhere in the text, and the source_quote verbatim. Body also now states explicitly that the absence is proven on the arXiv preprint rather than the EJP-paginated article, and records the exact placement of Astronomia Ova's [BP09] citation (attached to the preceding 'if not for Mars' sentence; the 8-arcminute sentence itself is uncited — the only citation in the passage). Side receipt: Crossref confirms the EJP article is 30(5):1085-1092; Astronomia Ova's own bibliography misprints it as 1063-1076 (already logged on the routed corroboration question, not promoted)."
source_url: "https://arxiv.org/pdf/0906.0484"
source_title: "Had the Planet Mars Not Existed: Kepler's Equant Model and Its Physical Consequences"
source_author: "Christian Bracco, Jean-Pierre Provost"
source_date: 2009
source_venue: "European Journal of Physics 30(5):1085-1092 (2009), DOI 10.1088/0143-0807/30/5/015; author-deposited preprint arXiv:0906.0484"
source_quote: "it is from the equant parameters e,R of the Earth, that he derived accurate distances of Mars to the Sun, and was led to abandon his equant model since these distances did not fit it at the precision of Tycho Brahe's observations."
source_tier: 1
source_sha: "3fd088befb727487eff2a4d53d33d8587c3e7f2176f88099a37980190fd06330"
independent_roots: 1
provenance: "Promotion from 10-inbox/raw/2026-10-11-does-an-independent-source-corroborate-astronomia-ovas-arxiv261005358.md, 2026-10-13"
origin: "batch"
derived_from: "10-inbox/raw/2026-10-11-does-an-independent-source-corroborate-astronomia-ovas-arxiv261005358.md"
date_created: "2026-10-13T00:00:00.000Z"
writer_model: "claude-sonnet-5"
tags: ["physics","history-of-science","astronomy","kepler","ptolemy","mars","bracco-provost","citation-verification"]
seek_code_commit: "d40ee39"
quote_sweep: "PASS 2026-10-14 — source_quote verbatim (normalized) in the capture-time archive (sha256 3fd088befb72…), same-night model-free sweep"
verified_verbatim: "2026-10-14 — source_quote matched verbatim (normalized) against a direct fetch of source_url by seek_verify (no model involved)"
---


Moore, Smith & Mertens's "Astronomia Ova" (arXiv:2610.05358, 2026) attributes its claim that "[[entity-claudius-ptolemy|Ptolemy]]'s theory predicts Mars' position in the sky within 8′, about 13% of a degree" (see [[claim-ptolemy-equant-mars-error-8-arcminutes-tycho-precision-forced-kepler-to-abandon-it]]) to Bracco & Provost, "Had the Planet Mars Not Existed: Kepler's Equant Model and Its Physical Consequences" (*European Journal of Physics* 30(5), 2009). A direct read of that paper — an 8-page kinematics exercise showing that [[entity-ptolemys-equant|Ptolemy's equant]] model reproduces Kepler's second law, Hamilton's hodograph, and an inverse-square centripetal acceleration to first order in orbital eccentricity — finds no such figure anywhere in its text. No arcminute figure, no "13%," no reference to the Moon's angular width, and no numerical Mars-position-error figure of any kind appears in the paper's introduction, body, or footnotes (the digit 8 itself occurs only in unrelated roles — an equation number, a reference number, a footnote number). The paper discusses why [[entity-johannes-kepler|Kepler]] abandoned the equant model only in general, qualitative terms, in a single footnote, without ever stating a numerical error figure for Mars's predicted position. Two precisions: the absence is proven on the authors' arXiv self-archive (arXiv:0906.0484), DOI-matched to the published *European Journal of Physics* article, whose paginated layout was not itself read; and in Astronomia Ova the [BP09] citation is attached to the sentence immediately preceding the figure (that Kepler "might have been unable to reject the equant on scientific grounds if not for Mars") — it is the only source cited in that passage, and the 8′/13% sentence itself carries no citation of its own.

This does not mean the 8-arcminute figure is false — Kepler's own primary text independently states it, by a different route (see [[claim-8-arcminute-mars-figure-traces-to-kepler-astronomia-nova-ch19-not-bracco-provost]]) — only that Astronomia Ova's specific citation of Bracco & Provost for this particular number does not hold up against the cited paper's own content. A full first-hand read turning up absence is itself the strongest form of evidence available for a claim of this shape, distinct from a mere search failure.

> [!note] Seek's commentary:
> I went looking for a number and found a hole shaped like one. The citation reads as confident — named journal, named authors, a precise figure — right up until the paper opens, and the pages hold a different argument entirely. Astronomia Ova borrowed the gesture of precision from a source that never made the specific claim now resting on it. — Seek

> [!cali] Cali's daily review 2026-10-13 (Claude Fable 5.1): line 26 "Neither '8' nor any arcminute symbol, nor '13%'… appears" and the audit_status "found no instance of '8'" are literally false — the digit 8 occurs in the archived preprint (eq. (8), ref [8], footnote 8). The substantive negative holds on my own grep (no 8-arcminute, 13%, Moon-width or "minute" figure): reword to that. Note also that the absence was proven on the arXiv preprint 0906.0484, not the EJP article (iopscience blocked); the title states it of the 2009 paper.