Computing Solar Eclipses — Research

Validation and error budget

workingupdated 2026-09-30validationerror-budgetsolar-radiusdelta-tpath-edge
  • Near-limit observations provide sensitive radius tests. The cited 0.37 arcsecond change shortens a central-line duration by 1.8 s and the Vale duration by 19.3 s. Published campaigns also include central-line observations 1 2.
  • The cited modern flash-spectrum and light-curve fits infer radii around 959.95 to 960.01 arcseconds. Earlier timing-based results also include lower values. Limb, detector and reduction models affect these estimates 2 1 3 4.
  • The cleanest 2024 edge test observed 13.7 s of totality where six public products predicted 12.9 s to 65 s. Only a true-limb model with the larger radius came within a second 5.
  • Limb omission, terrain omission and radius choices reach kilometres in cited edge cases. These shifts are not independent standard uncertainties. Remaining terms depend on the adopted corrections, geometry and measurement model 1 6.
  • A five-level test protocol can be assembled from published cases, from the 1961 Explanatory Supplement worked examples through the 2001 Lusaka limb corrections to the Vale, Stephenville and bead-timing records 7 8 4.

What this topic covers

This topic asks how far eclipse predictions have actually been shown to be right. It collects the published comparisons of timed contacts and Baily's bead events against predictions, sets the major public predictors side by side and names the input behind each disagreement, and assigns seconds of contact time and metres of path edge to every term in the error of a modern prediction. It ends with reference cases and tolerances a new implementation can be tested against.

Notes in this topic:

  • Observed versus predicted: the IOTA and IOTA/ES edge campaigns from 1973, the 2017 Vale and Thermopolis results, the 2023 Cape Range results and the 2024 Stephenville experiment, with the measured offsets.
  • Predictor disagreements: the inputs the NASA SVS, Espenak, Jubier, Irwin, USNO, timeanddate, Occult, Stellarium and Photo Ephemeris products state, and how far their edges and durations differ.
  • Error budget and validation protocol: the sourced per-term budget, the record of ΔT model validation, and the five-level test protocol with tolerances.

What this topic changes for the pipeline

The solar radius stops being a constant and becomes a configuration item with a stated uncertainty and two documented modes. Every product carries a per-run error estimate and draws its path limits as a band rather than a line. The five-level protocol becomes an automated test suite, with each reference case's constants pinned beside its tolerance.

References

  1. 1peer-reviewed Quaglia, Irwin, Emmanouilidis & Pessi (2021), Estimation of the Eclipse Solar Radius by Flash Spectrum Video Analysis, ApJS 256:36 Full PDF read (var/downloads/quaglia2021_flash_spectrum_ApJS.txt). Flash-spectrum video from a site a few hundred metres inside the 2017 southern limit near Vale, Oregon. S = 959.95 +/- 0.05 arcsec. Gives sensitivity of duration and limit distance to solar radius, and compares Irwin's model with Occult and Solar Eclipse Maestro.
  2. 2peer-reviewed Lamy, Prado, Floyd et al. (2015), A Novel Technique for Measuring the Solar Radius from Eclipse Light Curves, Solar Physics 290, 2617 Abstract page read. 17 photometer determinations over 2010, 2012, 2013, 2015 with Kaguya limb data. Average 959.99 +/- 0.06 arcsec at 540 nm.
  3. 3trade Guhl (2023), Baily's Beads Observation during the Hybrid Solar Eclipse 2023 April 20, Journal for Occultation Astronomy 2023-4, pp. 12-15 Full PDF read (var/downloads/JOA2023_4.txt). Northern limit of the total segment, Cape Range, Western Australia. Sixteen bead timings, mean correction +0.38 arcsec, result 960.01 +/- 0.12 arcsec.
  4. 4trade Guhl & Tegtmeier (2018), Baily's Beads Observations during the Total Solar Eclipse 2017 August 21, Journal for Occultation Astronomy 2018-3, pp. 19-21 Original PDF and paper extraction checked 2026-09-30. Southern video is overexposed and unreliable; no universal signed timing correction is given. Northern result 959.66 arcseconds. Original PDF SHA256 2ea6655d62dce0155e18a643d4fa2963d4935bb70a8e184008c65e071b57dbe9.
  5. 5trade Besselian Elements team, Experimentally Testing Eclipse Maps Accuracy (2024) Read via WebFetch summary. Stephenville, Texas, 2024 April 8. Observed totality 13.7 s (C2 18:39:06.6, C3 18:39:20.3 UTC) versus six predictions from 12.9 s (Irwin) to 65 s (timeanddate). Authors' own experiment, so trade grade.
  6. 6primary Espenak, Total Solar Eclipse of 2024 Apr 08, NASA GSFC interactive Google map page Full HTML read via curl (var/downloads/gsfc_SE2024Apr08Tgoogle.html). VSOP87/ELP2000-85 ephemerides, Delta T = 70.6 s, no limb profile, limits may shift 1 to 3 km, durations 1 to 3 s, greatest-duration point 10 to 20 km.
  7. 7peer-reviewed HMNAO and USNO (1961), Explanatory Supplement to the Astronomical Ephemeris, section 9 examples Local scan text read (var/downloads/es1961_djvu.txt). Worked examples 9.2 to 9.9 for the eclipse of 1961 February 15, usable as hand-checkable reference cases.
  8. 8primary Espenak & Anderson (2001), Total Solar Eclipse of 2001 June 21, NASA TP-2001-209484 Local text read (var/downloads/TP209484_2001.txt). DE200/LE200, Watts corrections of 0.4 arcsec, graze-zone accuracy +/- 0.3 arcsec, advice to stay 1 km inside the interior limit, Elev Fact terrain factor, consumer GPS +/- 100 m, worked Lusaka limb-correction example.

In this section

Observed versus predictedPublished comparisons of predicted and observed eclipse contacts and Baily's beads, including timed path-edge experiments in 2017 and 2024.workingPredictor disagreementsCompare solar eclipse predictors and the input choices behind differences in path limits and contact times for the 2017 and 2024 eclipses.workingError budget and validation protocolA validation protocol for eclipse calculation software, with reference cases, separate numerical and physical checks, and error-budget inputs.working