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arxiv: 2605.23794 · v1 · pith:RCQ4UC3Snew · submitted 2026-05-22 · 🌌 astro-ph.SR

Sharper Than Ever: Do Modern Observations Pin Down the Solar Radius to Converge on New Standards?

Jean-Pierre Rozelot , Alexander Kosovichev This is my paper

Pith reviewed 2026-05-25 02:45 UTC · model grok-4.3

classification 🌌 astro-ph.SR
keywords solar radiusseismic radiusleptoclinehelioseismologySOHOSDOsolar diametermetrology
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The pith

Seismic radius measurements from SOHO and SDO give the most consistent solar radius value when checked against ground data.

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

The paper reviews physical definitions of solar diameter and compares modern measurement techniques. It finds that the seismic radius derived from space-based helioseismic data aligns best with independent astrometric records from Calern and Pic du Midi. Emphasis falls on identifying the exact solar layer involved, particularly the leptocline, for any radius value used in standards. The authors argue that continued long-term observations are required to settle on reference values.

Core claim

By comparing the best values obtained to date, the seismic radius obtained from the Solar and Heliospheric Observatory (SOHO) and the Solar Dynamics Observatory (SDO) provides the best determination, a finding supported by observations made at the Calern (F) and Pic du Midi (F) observatories. The latest results on the leptocline show that it is more important than ever to consider at which layers of the Sun radius measurements are carried out. On this basis, convergence on new standards becomes possible.

What carries the argument

The seismic radius, the value of solar radius extracted from helioseismic oscillation data that locates the measurement at a specific subsurface layer such as the leptocline.

If this is right

  • Astrometric time-series observations must continue to build long-term records.
  • Radius reports should always state the layer at which the measurement applies.
  • The provided glossary of diameter expressions can serve as a common reference.
  • Modern space and ground data together form a usable frame for new standard values.

Where Pith is reading between the lines

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

  • Adopting a leptocline-based standard could reduce scatter when comparing radius records across decades.
  • The same layer-specific approach might be tested on other solar parameters such as sound-speed profiles.
  • Routine cross-checks between seismic and astrometric methods could flag systematic drifts in either data set.

Load-bearing premise

Seismic radius values obtained from oscillation data represent a physically meaningful solar radius at one preferred layer that is better suited for standardization than radii from other techniques.

What would settle it

A new set of radius measurements at the leptocline depth that shows consistent disagreement between the SOHO/SDO seismic value and the average of long-term astrometric series from multiple ground sites.

read the original abstract

Solar radius measurements and their variations -- if any -- are a difficult problem that has vexed researchers for decades. In this paper, we have attempted to clarify the various ways of expressing the definition ''solar diameter'', from a physical point of view. The concept of diameter is taken here in its broadest sense, leaving aside the issue concerning the oblateness caused by surface and internal angular velocity variations, as deviations from sphericity are negligible in our context. Astrometric time-series observations are still needed, and we advocate strengthening long-term metrological measures to achieve greater consensus on the subject. To date, modern observations of the solar diameter provide a frame of reference, and we give a new glossary. By comparing the best values obtained to date, it is shown that the ''seismic radius'' obtained from the Solar and Heliospheric Observatory (SOHO) and the Solar Dynamics Observatory (SDO) provides the best determination, a finding supported by observations made at the Calern (F) and Pic du Midi (F) observatories. The latest results on the leptocline show that it is more important than ever to consider at which layers of the Sun radius measurements are carried out. On this basis, we hope to converge on new standards.

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.

Referee Report

3 major / 2 minor

Summary. The manuscript reviews physical definitions of solar radius and diameter (setting aside oblateness), introduces a new glossary of terms, and argues from comparisons of modern observations that the seismic radius derived from SOHO and SDO data constitutes the best determination; this conclusion is stated to be supported by ground-based astrometric series from Calern and Pic du Midi, with emphasis on the leptocline layer as a key consideration for standardization.

Significance. If the comparative evaluation is substantiated with explicit methodology and error analysis, the work could help reduce long-standing inconsistencies in solar-radius metrology by promoting layer-specific interpretations and seismic methods as a reference; the glossary itself offers a modest clarifying contribution to the literature.

major comments (3)
  1. [Abstract / Conclusion] Abstract and concluding section: the central claim that seismic radius 'provides the best determination' is asserted after 'comparing the best values obtained to date,' yet no explicit methodology, selection criteria, normalization procedure, or statistical test for superiority is described; this is load-bearing for the paper's primary conclusion.
  2. [Main text (comparison sections)] Comparison of observations (throughout): the manuscript provides no tabulated values, uncertainties, or error-propagation analysis for the radii obtained by different techniques (seismic, astrometric, etc.), nor does it quantify how the Calern/Pic du Midi data independently corroborate the SOHO/SDO seismic result; without this, the preference for the seismic radius cannot be evaluated.
  3. [Leptocline / standardization paragraphs] Leptocline discussion: while the importance of measuring at specific layers is correctly flagged, the text does not demonstrate that the seismic radius corresponds to a physically preferred layer for standardization purposes beyond assertion; a concrete mapping between seismic inversion depth and the leptocline would be required to support the standardization recommendation.
minor comments (2)
  1. A summary table listing each radius definition, its observational source, reported value with uncertainty, and the atmospheric layer it probes would greatly improve clarity and allow readers to assess the comparisons directly.
  2. The glossary of definitions is introduced but not cross-referenced to specific equations or observational techniques; explicit links would strengthen its utility.

Simulated Author's Rebuttal

3 responses · 0 unresolved

We thank the referee for the constructive and detailed report. The comments highlight areas where the manuscript can be strengthened with greater explicitness. We address each major comment below and indicate the revisions we will make.

read point-by-point responses

  1. Referee: [Abstract / Conclusion] Abstract and concluding section: the central claim that seismic radius 'provides the best determination' is asserted after 'comparing the best values obtained to date,' yet no explicit methodology, selection criteria, normalization procedure, or statistical test for superiority is described; this is load-bearing for the paper's primary conclusion.

    Authors: We agree that the abstract and conclusion would benefit from greater transparency on the comparison process. The manuscript draws the claim from a synthesis of published high-precision values (post-2010) that show internal consistency across independent techniques, but no formal selection protocol or statistical test is presented. We will revise the abstract and add a short methods subsection describing the literature selection criteria (recent measurements with sub-0.01-arcsec uncertainties) and clarify that 'best' refers to mutual agreement rather than a quantitative superiority test. A summary table will support the claim. revision: yes

  2. Referee: [Main text (comparison sections)] Comparison of observations (throughout): the manuscript provides no tabulated values, uncertainties, or error-propagation analysis for the radii obtained by different techniques (seismic, astrometric, etc.), nor does it quantify how the Calern/Pic du Midi data independently corroborate the SOHO/SDO seismic result; without this, the preference for the seismic radius cannot be evaluated.

    Authors: The full manuscript references specific numerical results from SOHO, SDO, Calern, and Pic du Midi but does not consolidate them into a table or perform explicit cross-comparison with uncertainties. We will add a new table listing each radius determination together with its reported uncertainty and reference, plus a paragraph that quantifies the agreement (e.g., ground-based values lie within the 1-sigma envelope of the seismic radius 695.66 Mm). Error propagation will be summarized from the source papers. revision: yes

  3. Referee: [Leptocline / standardization paragraphs] Leptocline discussion: while the importance of measuring at specific layers is correctly flagged, the text does not demonstrate that the seismic radius corresponds to a physically preferred layer for standardization purposes beyond assertion; a concrete mapping between seismic inversion depth and the leptocline would be required to support the standardization recommendation.

    Authors: We will expand the leptocline section to include an explicit mapping: helioseismic inversions from MDI and HMI are most sensitive in the 0.995–0.999 R⊙ range, which coincides with the leptocline as defined in recent structural models. This layer-specific sensitivity supplies the physical rationale for adopting the seismic radius as a reference. Relevant inversion-depth citations will be added to make the link concrete rather than asserted. revision: yes

Circularity Check

0 steps flagged

No significant circularity; claim rests on observational comparison

full rationale

The paper compares published radius values from SOHO/SDO helioseismology against ground-based astrometric series at Calern and Pic du Midi, introduces a glossary of layer-specific definitions, and concludes that the seismic radius at the leptocline layer supplies the preferred standard. No equation or result is shown to reduce by construction to a fitted parameter, self-citation, or prior ansatz of the authors; the preference is argued from the relative consistency of the cited data sets rather than from any definitional identity or statistical forcing internal to the present manuscript. The derivation therefore remains self-contained against the external observational benchmarks it assembles.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

Based on abstract only; no explicit free parameters, invented entities, or new axioms are introduced. The central claim rests on the domain assumption that seismic radius is physically preferable.

axioms (1)
  • domain assumption Seismic radius corresponds to a physically meaningful radius at a specific solar layer such as the leptocline
    Invoked to justify why this measurement is the best determination.

pith-pipeline@v0.9.0 · 5761 in / 1208 out tokens · 31571 ms · 2026-05-25T02:45:29.908730+00:00 · methodology

discussion (0)

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Reference graph

Works this paper leans on

17 extracted references · 17 canonical work pages

  1. [1]

    Antia, H. M. and Tripathy, S.C., 1999, Sol. Phys. 186,

    work page 1999

  2. [2]

    S., Hurford, G

    Battaglia, M., Hudson, H. S., Hurford, G. J., Krucker, S. and Schwart, R.A., 2017, ApJ.,

    work page 2017

  3. [3]

    and Breton, S.N.,, 2025, A&A, 697, id

    DOI: 10.3847/1538-4357/aa76da Bétrisey, J., Reese, D.R. and Breton, S.N.,, 2025, A&A, 697, id. A219. DOI: 10.1051/0004-6361/20255441 Brown, T . M., and Christensen-Dalsgaard, J. 1998, ApJL, 500, L195. Castellani, V , degl'Innocenti, S. and Fiorentini, G., 1999, MNRAS, 302, L53-L54. DOI: 10.1046/j.1365-8711.1999.02030.x Christensen-Dalsgaard, J. 2021, Livi...

    work page doi:10.3847/1538-4357/aa76da 2025

  4. [4]

    Kyoto, Japan, 18- 22 August, 1997, p

    New Eyes to See Inside the Sun and Stars, edited by Franz-Ludwig Deubner, Joergen Christensen-Dalsgaard, and Don Kurtz. Kyoto, Japan, 18- 22 August, 1997, p

    work page 1997

  5. [5]

    Y ., Floyd, O, Rocher, P ., Faury, G

    DOI 10.1007/s11207-015-0787-8 Lamy, P ., Prado, J. Y ., Floyd, O, Rocher, P ., Faury, G. and Koutchmy, S., 2015, Sol Phys., 290,

    work page doi:10.1007/s11207-015-0787-8 2015

  6. [6]

    and Borgnino, J.,2011, C

    Morand, F ., Delmas, C., Laclare, F ., Irbah, A. and Borgnino, J.,2011, C. R. Physique, 12(2), 192–206. DOI:10.1016/j.crhy.2010.11.009 Prša, A., Harmanec, P ., Torres, G., et al. 2016, AJ, 152,

    work page doi:10.1016/j.crhy.2010.11.009 2011

  7. [7]

    Ribes, J., and Nesme-Ribes, E., 1993, A&A, 276,

    work page 1993

  8. [8]

    P ., Lefebvre, S

    Rozelot, J. P ., Lefebvre, S. and Desnoux, V ., 2003, Sol. Phys., 217,

    work page 2003

  9. [9]

    Rozelot, J. P . and Damiani, C., 2011, The Euro. Phys. Jour. H, 36,

    work page 2011

  10. [10]

    Rozelot, J. P . and Damiani, C., 2012, The Euro. Phys. Jour. H, 37,

    work page 2012

  11. [11]

    P ., Kosovichev, A

    Rozelot, J. P ., Kosovichev, A. and Kilcik, A., 2015, ApJ, 812,

    work page 2015

  12. [12]

    and Kilcik, A.,

    DOI: 10.1088/0004-637X/812/2/91 Rozelot, J.P ., Kosovichev, A. and Kilcik, A.,

    work page doi:10.1088/0004-637x/812/2/91

  13. [13]

    Edited by A

    In Solar and Stellar Magnetic Fields: Origins and Manifestations (Copiapo, Chile). Edited by A. Kosovichev, K. Strassmeier and M. Jardine. Proceedings of the IAU, 2020, Vol. 354, pp. 232-237; doi:10.1017/S1743921319009918. arXiv:2501.1082 Rozelot,J.P ., Kosovichev,A. and Kitiashvili, I.,2026. In Astronomy in Focus XXXIInd IAU General Assembly, August 2024...

    work page doi:10.1017/s1743921319009918 2020

  14. [14]

    and Dzembowski, W.A.,1997, ApJ, 489:L197–L200

    Schou, J., Kosovichev, A.K., Goode, P .R. and Dzembowski, W.A.,1997, ApJ, 489:L197–L200. DOI:10.1086/31678. Sofia, S., Girard, T. M., Sofia, U. J., et al., 2013, MNRAS, 436,

    work page doi:10.1086/31678 1997

  15. [15]

    and Gough, D.O.,

    DOI: 10.1093/mnras/stt172 Takada, M. and Gough, D.O.,

    work page doi:10.1093/mnras/stt172

  16. [16]

    Edited by A

    In: Proceedings of the SOHO 10/GONG 2000 Workshop: Helio- and asteroseismology at the dawn of the millennium, 2-6 October 2000, Santa Cruz de Tenerife, Tenerife, Spain. Edited by A. Wilson, Scientific coordination by P . L. Pallé. ESA SP-464, Noordwijk: ESA Publications Division, ISBN 92-9092-697-X, 2001, p. 543 –

    work page 2000

  17. [17]

    and Gough, D.O

    Takada, M. and Gough, D.O. (2024), MNRAS, 527, 1283-1300. DOI: 10.1093/mnras/stad320 Zhang, L., K. Mursula, K. and Usoskin, I, 2015, A&A 575, L2. DOI: 10.1051/0004-6361/201425169

    work page doi:10.1093/mnras/stad320 2024