arxiv: 2604.24503 · v1 · submitted 2026-04-27 · 🌌 astro-ph.SR · physics.hist-ph· physics.space-ph

Recognition: unknown

Analyses on Wassenius' Report for Total Solar Eclipse in 1733: Quantifications of the Solar Radius and the Earliest Reported Prominences

Hisashi Hayakawa , Mitsuru S\^oma , Noortje Peek , Jean-Pierre Rozelot , Stanislav Gun\'ar , Alexei Pevtsov

Authors on Pith no claims yet

Pith reviewed 2026-05-08 01:31 UTC · model grok-4.3

classification 🌌 astro-ph.SR physics.hist-phphysics.space-ph

keywords solar radiussolar prominencestotal solar eclipse1733solar minimumhistorical astronomypolar prominences

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The pith

A 1733 eclipse report yields a solar radius of 696250 km and places the earliest reported prominences at high latitudes during solar minimum.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper translates and reanalyzes Wassenius' original account of the total solar eclipse visible in Sweden in 1733. It converts his timing notes and descriptions of features into quantitative measurements, producing a solar radius value in both absolute and angular units. The derived radius is slightly larger than the modern standard but matches a measurement from the 1715 eclipse. The account also includes descriptions of three prominences whose positions are calculated at high heliographic latitudes, which the authors use to classify the year as a solar minimum and link the features to possible polar rush activity.

Core claim

From Wassenius' descriptions of the 1733 total solar eclipse, the solar radius is quantified as 696250 +/- 170 km (absolute) and 959.99 +/- 0.24 arcseconds (apparent), which differs from the modern helioseismic value of 695780 +/- 160 km but agrees with the 1715 record. Three prominences are located at heliographic latitudes of +23.5 +/- 22.5 degrees, +66.5 +/- 22.5 degrees, and -68.5 +/- 22.5 degrees, appearing at latitudes higher than expected from the sunspot butterfly diagram for that period and thereby confirming 1733 as a solar minimum; at least two are classified as quiescent prominences, implying the presence of a polarity inversion line in the polar regions.

What carries the argument

Conversion of the observer's qualitative timing of eclipse contacts and positional descriptions of prominences into precise angular sizes of the solar disk and heliographic latitude coordinates.

If this is right

The Sun's radius in 1733 was approximately 470 km larger than the current standard value.
Solar prominences formed at high latitudes during the 1733 solar minimum, unlike the typical sunspot distribution.
If the high-latitude prominences are polar rush features, the solar minimum date must be shifted to before May 1733.
At least two of the prominences qualify as quiescent, indicating polarity inversion lines existed in the polar regions in early 1733.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

Historical eclipse reports may allow tracking of possible slow changes in solar radius over centuries.
The re-dating of the minimum could adjust reconstructions of solar activity levels in the early 18th century.
Such analyses demonstrate how single eyewitness accounts can be turned into testable data on solar cycle behavior.

Load-bearing premise

Wassenius' qualitative descriptions of timing, duration, and prominence locations can be converted into precise angular measurements without large systematic errors from his instruments or personal perception.

What would settle it

An independent modern eclipse observation or helioseismic measurement that yields a solar radius near 695780 km, or a reconstruction showing that high-latitude prominences do not occur at solar minimum.

Figures

Figures reproduced from arXiv: 2604.24503 by Alexei Pevtsov, Hisashi Hayakawa, Jean-Pierre Rozelot, Mitsuru S\^oma, Noortje Peek, Stanislav Gun\'ar.

**Figure 1.** Figure 1: Wassenius’ sketches of the eclipsed Sun and prominences on 1733 May 13, as reproduced view at source ↗

**Figure 2.** Figure 2: Lunar-limb profiles in comparison with different solar-limb profiles, setting R☉ = 696080 km (left) and R☉ = 696420 km (right), where the solar photosphere touches the bottom of the deepest lunar valleys. The position angles are measured from the direction of celestial north. The lunar topography data are derived from KAGUYA Mission (Araki et al., 2009), following the method of Sôma et al. (2012). The luna… view at source ↗

**Figure 3.** Figure 3: Eclipse-based R☉ measurements in comparison with the modern standard R☉ (959.34″; Takata and Gough, 2024), where our R☉ constrain is indicated by the red bar and the R☉ constrains of the previous studies by blue bars (Kubo, 1993; Kilcik et al., 2009; Lamy et al., 2015; Quaglia et al., 2021). During this TSE, the Moon was ≈ 357778 km away from the observational site according to calculations performed using… view at source ↗

**Figure 4.** Figure 4: Heliographic coordinate of the eclipsed Sun at the maximum of the TSE in 1733, as seen view at source ↗

**Figure 5.** Figure 5: Our measurement for the heliographic latitudes of Wassenius’ prominences (bars in light blue), in comparison with the contemporaneous sunspot position datasets (Arlt, 2008, 2018; Hayakawa et al., 2022) and the International Sunspot Number V2 (ISN V2: Clette et al., 2023). We need to be cautious on the reliability of the International Sunspot Number V2 before 1749, as the recent studies suggested substantia… view at source ↗

read the original abstract

Total solar eclipses (TSEs) offer a unique opportunity to observe the solar atmosphere, detect limb phenomena, and accurately measure the solar radius. Following the TSE in 1733, Wassenius first reported the existence of prominences to the scientific community. Wassenius' original manuscript is held in the Royal Academy Archives of Sweden; this study translates his report and documents the associated source materials and local eclipse visibility. The solar radius (R_Sun) during the TSE in 1733 are 696250 +/- 170 km and 959.99 +/- 0.24" in the absolute and apparent scales, respectively. This result contrasts with the modern standard (helioseismic) R_Sun of 695780 +/- 160 km and 959.34 +/- 0.22"; however, it is consistent with the solar radius recorded in 1715. The observed prominences are located at +23.5 +/- 22.5{\deg}, +66.5 +/- 22.5{\deg}, and -68.5 +/- 22.5{\deg} in the heliographic latitude. The appearance of prominences at such high latitudes contrasts with the sunspot butterfly diagram for 1725-1750, confirming 1733 as a solar minimum. These high-latitude prominences can potentially be attributed to the so-called 'polar rush' prominences that appear a few years after a solar minimum. If they are categorised as 'polar rush' prominences, the solar minimum must be re-dated to before 1733 May. Furthermore, the latitudes of at least two of the prominences reported by Wassenius enable their classification as quiescent prominences, suggesting the presence of a polarity inversion line in the polar regions in early 1733.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Desk Editor's Note private letter to a colleague

This paper extracts new radius and prominence latitude numbers from Wassenius' 1733 eclipse report with explicit error bars, but the large uncertainties keep the high-latitude and solar-minimum claims only suggestive.

read the letter

The core contribution is a fresh reduction of the original Wassenius manuscript into a solar radius of 696250 +/- 170 km and prominence latitudes around +23.5, +66.5, and -68.5 degrees, each with +/-22.5 degree errors. The authors translate the narrative timing and descriptions into angular quantities using eclipse geometry, compare the radius to the 1715 value and modern helioseismic standard, and link the high-latitude prominences to possible polar-rush behavior and a possible earlier solar minimum date. They also classify at least two as quiescent based on latitude. This is genuine new data extraction from a primary source that prior literature had not quantified this way, and the error propagation is shown explicitly rather than hidden. The work sits on solid historical grounding and cites the relevant eclipse studies without circularity. The radius offset from modern values falls near the edge of the combined uncertainties, and the latitude errors span both mid- and high-latitude ranges, so the claimed contrast with the 1725-1750 butterfly diagram is not decisive. The conversion from qualitative description to precise angles assumes Wassenius' personal timing and perception introduced no large systematic offsets beyond the stated bars; that assumption is reasonable for a first pass but would benefit from more sensitivity tests on instrument limits and observer bias. The paper is aimed at researchers reconstructing solar-cycle behavior and radius variations over centuries. Anyone working on historical solar data or long-term activity proxies will find the new numbers useful as an additional data point. It deserves peer review because the methods are transparent, the source is primary, and the community can judge whether the error bars support the interpretive steps. I would send it out rather than desk-reject.

Referee Report

3 major / 2 minor

Summary. The manuscript translates Wassenius' 1733 total solar eclipse report from the original Swedish manuscript and derives quantitative values for the solar radius and the heliographic latitudes of three reported prominences. It obtains R_Sun = 696250 ± 170 km (absolute) and 959.99 ± 0.24 arcsec (apparent), slightly larger than the modern helioseismic values, and places the prominences at +23.5 ± 22.5°, +66.5 ± 22.5°, and -68.5 ± 22.5°. These latitudes are interpreted as high-latitude activity confirming a solar minimum in 1733, with possible attribution to polar-rush prominences that would require re-dating the minimum to before May 1733.

Significance. If the conversions from narrative descriptions to angular quantities prove robust, the work supplies one of the earliest quantified prominence observations and a historical eclipse-based solar-radius measurement. Explicit error bars on both radius and latitudes are a clear strength, enabling direct statistical comparison with modern data and with the 1715 eclipse radius. The polar-rush hypothesis offers a testable link to solar-cycle dynamics.

major comments (3)

[Prominence latitude derivation] Prominence latitude section: the reported ±22.5° uncertainties imply that the +23.5° feature spans +1° to +46°. This range overlaps both mid- and high-latitude regimes and therefore does not unambiguously support the claim that the observations 'contrast with the sunspot butterfly diagram' or confirm 1733 as a solar minimum.
[Solar radius quantification] Solar radius quantification: the 470 km offset from the modern value (696250 ±170 km vs. 695780 ±160 km) lies near the edge of the combined 1-σ interval (~230 km). The manuscript does not demonstrate that all systematic contributions from timing accuracy, instrument resolution, and eclipse geometry have been folded into the quoted ±170 km; an unrecognized offset in any single timing datum could move the result inside or outside the modern value.
[Methods] Methods for angular conversion: the translation of Wassenius' qualitative timing and position descriptions into sub-arcminute and 22.5°-precision quantities assumes negligible perceptual and instrumental bias. No sensitivity table or Monte-Carlo propagation of plausible timing errors (e.g., ±1 min) is provided, leaving the central claims dependent on unquantified interpretive steps.

minor comments (2)

[Abstract] Abstract: 'The solar radius (R_Sun) during the TSE in 1733 are 696250' contains a subject-verb agreement error; 'is' is required.
[Figures/Tables] Figure or table captions should explicitly list the sources of the quoted uncertainties (timing, geometry, perception) so readers can assess their completeness without returning to the text.

Simulated Author's Rebuttal

3 responses · 0 unresolved

We thank the referee for the thoughtful and detailed report. The comments highlight important points regarding the robustness of our quantitative derivations and the strength of our interpretive claims. We have revised the manuscript to address each major comment, adding clarifications, sensitivity analyses, and moderated language where appropriate. Our responses are given point by point below.

read point-by-point responses

Referee: [Prominence latitude derivation] Prominence latitude section: the reported ±22.5° uncertainties imply that the +23.5° feature spans +1° to +46°. This range overlaps both mid- and high-latitude regimes and therefore does not unambiguously support the claim that the observations 'contrast with the sunspot butterfly diagram' or confirm 1733 as a solar minimum.

Authors: We agree that the ±22.5° uncertainty on the +23.5° prominence permits values as low as +1°, which overlaps the mid-latitude regime and weakens a strict high-latitude classification for that feature alone. The other two prominences remain unambiguously high-latitude. In the revised manuscript we have updated the relevant section to state that at least two prominences are at high latitudes, which remains consistent with solar-minimum conditions, while noting the ambiguity for the third. The claim of contrast with the butterfly diagram has been softened to 'is consistent with' rather than 'confirms,' and a short paragraph discussing possible interpretations has been added. revision: partial
Referee: [Solar radius quantification] Solar radius quantification: the 470 km offset from the modern value (696250 ±170 km vs. 695780 ±160 km) lies near the edge of the combined 1-σ interval (~230 km). The manuscript does not demonstrate that all systematic contributions from timing accuracy, instrument resolution, and eclipse geometry have been folded into the quoted ±170 km; an unrecognized offset in any single timing datum could move the result inside or outside the modern value.

Authors: The ±170 km uncertainty was obtained by propagating the timing and geometric measurement errors reported by Wassenius. We acknowledge that the manuscript did not explicitly demonstrate inclusion of all possible systematics such as instrument resolution or observer bias. In the revision we have added an expanded error-budget subsection that includes a Monte-Carlo exploration of ±1 min timing offsets and plausible variations in eclipse geometry. The results show that the derived radius stays within ~2σ of the modern value and remains consistent with the 1715 eclipse measurement. We have also inserted a caveat paragraph noting that unrecognized systematics could shift the result. revision: yes
Referee: [Methods] Methods for angular conversion: the translation of Wassenius' qualitative timing and position descriptions into sub-arcminute and 22.5°-precision quantities assumes negligible perceptual and instrumental bias. No sensitivity table or Monte-Carlo propagation of plausible timing errors (e.g., ±1 min) is provided, leaving the central claims dependent on unquantified interpretive steps.

Authors: We accept that the original methods section lacked a quantitative sensitivity study of the interpretive steps. The revised manuscript now contains a dedicated sensitivity table that varies the adopted timings by ±30 s to ±2 min and recomputes both the solar radius and prominence latitudes. A brief Monte-Carlo summary is also provided, confirming that the central values and quoted uncertainties are stable under these perturbations. These additions are placed in a new subsection of the Methods. revision: yes

Circularity Check

0 steps flagged

No significant circularity; central derivations are from historical text and eclipse geometry

full rationale

The paper translates Wassenius' 1733 report, applies standard eclipse geometry and timing data to compute R_Sun (absolute and apparent) and heliographic latitudes of prominences. These steps start from the observer's qualitative descriptions and known local circumstances rather than from fitted parameters or prior results by the same authors. Modern helioseismic R_Sun appears only in post-hoc comparison, not as an input or constraint. No self-definitional loops, renamed predictions, or load-bearing self-citations are present in the derivation chain.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central results rest on the assumption that the observer's narrative can be mapped to angular positions via standard eclipse geometry; no new physical entities are introduced.

axioms (1)

standard math Standard spherical geometry and eclipse projection formulas apply to convert observed timings and positions into heliographic coordinates.
Invoked when deriving latitudes and radius from the manuscript descriptions.

pith-pipeline@v0.9.0 · 5680 in / 1137 out tokens · 36507 ms · 2026-05-08T01:31:10.238385+00:00 · methodology

discussion (0)

Reference graph

Works this paper leans on

23 extracted references · 15 canonical work pages

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Figure 1: Wassenius’ sketches of the eclipsed Sun and prominences on 1733 May 13, as reproduced from MS Wassenius (f

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