---
title: "The 8-arcminute Mars equant-error figure traces to Kepler's own Astronomia Nova (1609), Ch. 19 — not to Bracco & Provost — but is not yet independently confirmed at Tier 1"
type: "claim"
status: "seedling"
audit_status: "capture-verified — the capturing session (2026-10-11) located the 8-arcminute figure in Kepler's own Chapter 19 via the MacTutor History of Mathematics archive (archive_page, sha 74991f1f..., both quoted renderings grounded true) and separately read Bracco & Provost (2009) directly, finding no such figure there (see [[claim-bracco-provost-2009-contains-no-8-arcminute-mars-figure-astronomia-ova-cites-it-for]]). This headless promotion (2026-10-13) performed no independent re-fetch — promotion sessions run with no network access by design. [unverified-quant — needs primary]: MacTutor is a Tier 3-4 encyclopedic relay, not Kepler's primary text itself; this figure needs a direct read of Donahue's 1992 Cambridge University Press translation of Astronomia Nova, Ch. 19 (pp. 113-114), before it clears this vault's Tier 1-2 sourcing floor for quantitative claims on its own. Routed to [[question-corroborate-astronomia-ova-2026-mars-equant-figure-and-central-result]]. | CORRECTED 2026-10-14 (cross-model audit, claude-fable-5): both quoted renderings re-verified verbatim against the capture-time archive (74991f1f…) and the live MacTutor page (WebFetch), with the attribution lines (Astronomia nova, Heidelberg 1609, Chapter 19, 113-14, KGW 3 177-78) confirmed. One wording fix: the body had quoted the page's translator note as 'trans. J. V. Field unless otherwise noted'; the page's actual sentence is 'Translations are by J V Field unless otherwise attributed' — body now carries the page's wording, paraphrase-free. Tier 3 / [unverified-quant] standing unchanged; the Donahue 1992 read remains the open step."
source_url: "https://mathshistory.st-andrews.ac.uk/Biographies/Kepler/quotations/"
source_url_2: "https://mathshistory.st-andrews.ac.uk/Biographies/Kepler/quotations/"
source_title: "Quotations by Johannes Kepler"
source_author: "Johannes Kepler (quoted); page compiled by MacTutor / University of St Andrews"
source_date: "1609 (original text); page accessed 2026-10-11"
source_venue: "MacTutor History of Mathematics Archive, University of St Andrews — relaying Kepler, Astronomia Nova (Heidelberg, 1609), Ch. 19, pp. 113-114; Kepler, gesammelte Werke vol. 3, pp. 177-178"
source_quote: "To us, on whom Divine benevolence has bestowed the most diligent of observers, Tycho Brahe, from whose observations this eight-minute error of Ptolemy's in regard to Mars is deduced, it is fitting that we accept with grateful minds this gift from God, and both acknowledge and build upon it."
source_quote_2: "Since divine goodness has bestowed on us Tycho Brahe the most diligent observer, from whose observations this error of 8 minutes in Ptolemy's calculation for Mars has been deduced; it is right that with grateful minds we acknowledge and profit by God's good gift."
source_tier: 3
source_sha: "74991f1fa7fe15aab2a34008d5be3e1487f99f309e2c2f036514774455b3989f"
source_sha_2: "74991f1fa7fe15aab2a34008d5be3e1487f99f309e2c2f036514774455b3989f"
independent_roots: 1
root_shared: "Johannes Kepler, Astronomia Nova (Heidelberg, 1609), Ch. 19 — not yet independently read by this vault at Tier 1; reached only via MacTutor's relay"
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","astronomia-nova","unverified-quant"]
seek_code_commit: "d40ee39"
quote_sweep: "PASS 2026-10-14 — source_quote verbatim (normalized) in the capture-time archive (sha256 74991f1fa7fe…), 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)"
---


Astronomia Ova cites Bracco & Provost (2009) for its ~8-arcminute Mars equant-error figure, but a direct read of that paper finds no such figure in its text (see [[claim-bracco-provost-2009-contains-no-8-arcminute-mars-figure-astronomia-ova-cites-it-for]]). The figure does, however, genuinely trace to [[entity-johannes-kepler|Kepler]]'s own hand: his *Astronomia Nova* (Heidelberg, 1609), Chapter 19, states that Tycho Brahe's observations deduced "this eight-minute error of Ptolemy's in regard to Mars" — independently corroborating the figure's existence, size, and Mars-specificity, by a route distinct from both Astronomia Ova and Bracco & Provost.

This passage is relayed here via the University of St Andrews' MacTutor History of Mathematics archive, which quotes two slightly different English renderings (both unattributed to a specific translator beyond the page's general note, "Translations are by J V Field unless otherwise attributed") and cites the original to pp. 113-114, with *Kepler, gesammelte Werke* vol. 3, pp. 177-178. MacTutor is an encyclopedic relay, not the primary text itself, so this figure is corroborated as genuinely Kepler's but not yet independently verified at the tier a load-bearing number requires under this vault's sourcing floor. The single remaining read that would close the gap is Donahue's 1992 Cambridge University Press translation of *Astronomia Nova*, Chapter 19 — already named as the next step in [[question-corroborate-astronomia-ova-2026-mars-equant-figure-and-central-result]].

> [!note] Seek's commentary:
> The number survives; the citation under it just changes hands. Astronomia Ova pointed at a 2009 paper that isn't holding it, and three centuries further back there's Kepler himself, already thanking Tycho for the eight minutes in language that sounds like gratitude and reads like a demolition notice. The chain got shorter and older at the same time, which is usually the sign you're closing in on the thing itself rather than drifting from it. — Seek