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On the orientation of historic Christian churches of Fuerteventura: conciliating tradition, winds and topography

T0 review · 3 major / 3 minor · reviewed 2026-08-15 · deepseek-v4-flash

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Pith's one-line read The measured axes of 48 Fuerteventura churches concentrate in two groups: one aimed slightly north of east, tied to Easter sunrise, and one near declination −14° that the paper leaves open to four readings.

desk verdict Solid survey data, over-interpreted peaks: the Fuerteventura orientation table is the contribution; the two declination groups and Easter test don't survive their own statistics. read the letter →

arxiv 2505.18161 v1 pith:DNCPM2MG submitted 2025-05-11 physics.hist-ph astro-ph.IMphysics.soc-ph

Maria Florencia Muratore , Alejandro Gangui , Maitane Urrutia-Aparicio , Carmelo Cabrera , Juan Antonio Belmonte This is my paper · ORCID
classification physics.hist-phastro-ph.IMphysics.soc-ph
keywords archaeoastronomychurchorientationadorientemFuerteventuraCanaryIslandsEastersunriseSiriusdeclinationcurvigram
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

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

The reading

The paper measures the altar orientations of 48 colonial-era churches on Fuerteventura and asks whether builders followed the Christian rule that the apse face the rising Sun. It finds that about 70% of the sample, and 91% of pre-20th-century buildings, lie within the solar arc, so the tradition was largely respected. The declination distribution shows two prominent concentrations: a peak near +5°, slightly north of due east, which the authors link to sunrise on Easter Sunday near the construction date, and a peak near −14° concentrated in central-island churches, for which they weigh four non-exclusive explanations: Easter sunset, the local All Souls' vigil "Los Finaos", the 105° azimuth of central valleys, and the star Sirius, known locally as the Gañanera. None of the four is conclusive, and the paper also notes that many canonical churches add a south-facing side door, reconciling tradition with the island's strong trade winds.

What carries the argument

The analysis is carried by the declination curvigram: each measured azimuth and horizon height is converted into a solar declination δ using standard positional-astronomy formulae, then smoothed with an Epanechnikov kernel whose bandwidth is twice the mean measurement error of 0.7°. The resulting density is normalized by the mean of 100 random subsamples drawn from a uniform azimuth distribution over a flat horizon at a mean island latitude of 28.5°N, and peaks rising above three standard deviations are treated as potentially significant. The same conversion from declination to calendar dates lets the authors match the +5° peak to Easter Sundays near construction years and the −14° peak to dates such as 2 November, while a Kolmogorov-Smirnov test against random distributions is used to frame what the normalized peaks can and cannot establish.

What would settle it

Recompute the curvigram using actual horizon profiles and local latitude for every church, then re-run the 3σ significance test; if the +5° and −14° peaks no longer exceed the threshold, the two-group structure is an artifact of the flat-horizon normalization.

Watch

Extended reading notes

Core claim

On the paper's own terms, the discovery is that most measured churches, 34 of 48, keep their main axes within the solar range, and the sample's declination curvigram, normalized against a uniform azimuth distribution, shows two peaks above the 3σ threshold: a principal maximum at δ ≈ +5° and a secondary maximum at δ ≈ −14°. The +5° peak is interpreted as Easter sunrise orientation, because for a dozen churches with declinations in the +5±5° range there is an Easter Sunday in the years around construction whose solar declination matches. The −14° peak is treated as anomalous; the authors explicitly reject patron-saint dates, magnetic compass use, and wind avoidance as explanations, then present Los Finaos, local valley topography, Easter sunset, and Sirius as candidate causes, with the stellar reading called speculative and supported only by circumstantial ethnographic and iconographic evidence.

Load-bearing premise

The reality of the two orientation groups depends on a null model that assumes a flat horizon, a single island-wide latitude, and a smoothing width of twice the mean error—and the paper's own Kolmogorov-Smirnov tests, a standard goodness-of-fit check, cannot reject that the whole sample is random.

Editorial extensions

If this is right

  • If the Easter-sunrise reading of the +5° peak is correct, Fuerteventura's builders followed a movable feast rather than the fixed equinoctial east, matching a practice found in the Castilian regions that supplied the colonizers.
  • If the −14° group is real, it marks a local orientation custom with no parallel in the previously surveyed Canary Islands; the paper's four candidate explanations all remain open.
  • The finding that pre-20th-century churches are 91% within the solar range, while most exceptions are modern or private chapels, implies the liturgical tradition remained normative on the island until recent times.
  • The south-facing side-door pattern gives a concrete architectural mechanism for reconciling canonical eastward orientation with the prevailing trade winds, distinct from Lanzarote's whole-building rotation.
  • Completing the survey on Gran Canaria would test whether these patterns are specific to Fuerteventura or common to the archipelago's colonial churches.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • A sharper test of the −14° group than the paper performs would separate the four hypotheses by horizon: churches on flat, open ground cannot be explained by valley topography, so any of them that still fall near −14° would point to Los Finaos, Easter sunset, or Sirius rather than terrain.
  • If the Easter-peak interpretation is right, the orientation scatter should correlate with the year of construction: the +5° peak would be tighter where parish archives fix the building date and wider where dates are uncertain, which could be checked against the church account books the paper cites.
  • Applying the same measurement protocol on Gran Canaria would be a natural out-of-sample test: if the two-group pattern is a real island tradition it should appear there too, while if it is local topography it should track that island's different valley systems.
  • The star and rosette plaques on the Agua de Bueyes barbican could motivate a focused ethnographic survey of Gañanera observation practices in the central island before the Sirius alignment is taken beyond speculation.
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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Referee Report

3 major / 3 minor

Summary. The paper presents field measurements of the orientations of 48 historic churches and chapels on Fuerteventura, listing for each building the azimuth, horizon height, and computed solar declination with uncertainties. The descriptive claim is that the great majority of pre-20th-century constructions (91%) fall within the solar range, and that wind avoidance is accommodated through south-facing lateral doors rather than through non-canonical orientations. The paper further claims that the declination distribution contains two notable groups: a peak near delta = +5 degrees, interpreted as orientation to the sunrise on Easter Sundays near the construction date, and a peak near delta = -14 degrees, concentrated in central-island churches and attributed speculatively to Los Finaos, valley topography, sunset orientations, or Sirius (the Gañanera). The stated statistical basis for the two-group claim is the normalized curvigram in Figure 8 with a 3-sigma threshold, despite the paper's own Kolmogorov-Smirnov tests failing to reject random null distributions.

Significance. If the two-group interpretation were established, the paper would make a useful contribution to Canarian archaeoastronomy, connecting colonial church orientations with Iberian Easter-orientation traditions and with local ethnographic stellar lore. The descriptive dataset itself is valuable: the measurements are carefully documented, with corrected magnetic azimuths, horizon-height estimates, error propagation, a full table, maps, and comparisons with previous studies on Lanzarote and La Gomera. The paper also offers a sensible practical explanation, the south-facing lateral door, for reconciling canonical orientation with prevailing winds. However, the identification of the two declination groups is the load-bearing claim of the abstract, and it is not currently supported by the statistical tests presented in the manuscript.

major comments (3)
  1. [Data sample and methods; Results, Fig. 8] The paper's own formal tests contradict the claim that the two declination groups are statistically established. In the methods section the authors state that the Kolmogorov-Smirnov tests 'indicated that we cannot discard the null hypothesis with confidence' for both the uniform and the solar distributions, and they acknowledge that the maxima 'might have the same relative frequency when compared to an individual random distribution.' Despite this, the Results section and the abstract treat the +5 and -14 degree peaks as a statistically revealed two-group structure, with the 3-sigma threshold in Fig. 8 as the criterion. That threshold is not an independent test: it is obtained by normalizing the empirical curvigram against 100 random samples drawn from a uniform azimuth distribution with a flat horizon and a single mean latitude of 28.5 degrees N, and with the kernel bandwidth fixed to twice the mean error. A uniform-in-azimuth null is inappropriate for detecting an excess of easterly orientations, because any concentration inside the narrow solar arc will tend to look significant against it. The claim should either be re-derived with a null that respects the expected easterly distribution and the actual horizon and latitude of each church, or explicitly relabeled as a descriptive rather than statistically significant pattern.
  2. [Table 2 and Discussion (Easter test)] The test for Easter orientation is circular in effect. Churches are selected for Table 2 precisely because their declination lies in the range +5 +/- 5 degrees, and then Easter Sundays are located in a range of years near the often poorly constrained construction date whose solar declination matches that value. Because Easter Sunday moves across a roughly month-long interval and construction dates carry large uncertainties, such a match is almost guaranteed; the authors themselves concede that 'given a church value of declination, it is not difficult to find a Sun's declination close to it but occurring during Easter Sunday in a small range of years around the date of construction.' This does not discriminate Easter sunrise from an equinoctial orientation or from any date within the same season. The interpretation would need a control, for example the same matching exercise with non-Easter dates or with a null distribution of movable feasts, together with a propagation of construction-date uncertainty.
  3. [Discussion (-14 degree peak); churches 29-33] The -14 degree peak is not robust against the topographical explanation that the authors themselves offer. Churches 29, 30, 31, and 33 are described as located in valleys that descend toward the sea near 105 degrees in azimuth with very low or negative horizon heights; this geometry alone produces declinations near -14 degrees even without any shared calendrical or stellar intention. Because these same churches are the main contributors to the peak, the 'second group' may be an artifact of valley orientation rather than a separate cultural tradition. The Sirius hypothesis does not resolve this: the 17th-century declination of Sirius (-16.3 degrees) differs from -14 degrees by more than the stated uncertainties, and the one church discussed under that hypothesis (no. 8, Agua de Bueyes) has its altar direction at delta about +19 degrees, so its narthex direction is being used in the opposite sense; that church is not itself part of the -14 degree peak. A quantitative test comparing the valley-church orientations with the distribution of local valley axes would be needed before treating the -14 degree concentration as a distinct group.
minor comments (3)
  1. [Data sample and methods] The test name is misspelled as 'Kolmogorov-Smirnoff'; it should be 'Kolmogorov-Smirnov'.
  2. [Historic churches of Fuerteventura] The text says San Isidro Labrador was built in 1714, while Table 1 lists 1713; please reconcile these dates.
  3. [Results, Fig. 8] The sentence describing the normalized curvigram as 'including geographical location and local topography' is misleading: the normalization uses a flat horizon and a single mean latitude, and only the measured horizon heights of individual churches enter the declination computation. Please rephrase to avoid implying that the null model includes local topography.

Circularity Check

1 steps flagged · score 6.0 of 10

Easter-orientation interpretation is circular: the +5°±5° declination selection already coincides with the range of Easter sunrise declinations, so the Table 2 match is guaranteed by construction.

  1. fitted input called prediction [Discussion, Table 2 and preceding text (p. 18)]
    "To test this hypothesis, we consider all churches with declination values some five degrees on both sides of the δ = +5º peak and check the possible Easter dates matching their declination (see Table 2). ... From Table 2 we can verify that given a church value of declination, it is not difficult to find a Sun’s declination close to it but occurring during Easter Sunday in a small range of years around the date of construction."

    The churches in Table 2 are selected by the condition δ ≈ +5°±5°. Easter Sunday is constrained by ecclesiastical computus to 22 March–25 April; over the Gregorian cycle its solar declination at the island's latitude sweeps the same interval (roughly 0° to +13°). Hence the subsequent 'discovery' that each selected church has an Easter-Sunday solar declination matching its measured declination in some nearby year is a direct consequence of the selection cut plus the variable date of Easter, not an independent confirmation. The test cannot fail for a church in the selected window, so the Easter interpretation is supported by construction rather than by evidence. The paper's own admission that the match is 'not difficult to find' confirms the lack of discriminative power.

full rationale

The paper's descriptive core is self-contained: the claim that 70% of the sample, and 91% of pre-20th-century churches, fall within the solar range is supported directly by the measured azimuths and is not circular. The -14° peak discussion is also not circular in the technical sense: the authors explicitly list topography and Los Finaos as alternative explanations and state that none of the four hypotheses is conclusive. The circularity is localized to the Easter-orientation proposal: the test set is defined by a declination window that already encompasses the declinations attainable by Easter Sundays, and the variable date of Easter makes a match essentially unavoidable. This makes the 'prediction' of Easter orientations a restatement of the sample-selection criterion. The Kolmogorov-Smirnov and 3σ-significance concerns are real statistical fragility but are not definitional circularity, so they do not enter the score beyond the partial circularity already identified.

Assumptions & free parameters 3 free parameters · 3 assumptions · 0 invented entities

No new physical or astronomical entities are postulated. The Gañanera is the local name for Sirius, documented in prior ethnographic work (Belmonte and Sanz de Lara 2020).

free parameters (3)
  • Easter declination selection window = +5 +/-5 degrees
    Churches with declination within this range were selected to test the Easter hypothesis; the window is centered on the observed principal maximum of the curvigram, so it is chosen after seeing the data.
  • Kernel bandwidth = 1.4 degrees (twice the mean error)
    The KDE bandwidth is set to twice the mean declination uncertainty (0.7 degrees); this choice affects the width and significance of peaks in Figure 8.
  • Mean latitude for null distributions = 28.5 degrees N
    The uniform and solar null distributions are generated at the latitude of Puerto del Rosario; using other latitudes or actual horizon profiles would change the expected distributions and the 3 sigma threshold.
assumptions (3)
  • domain assumption The current measured axis of each building (from back to altar) corresponds to the original liturgical orientation, despite later reforms and enlargements.
    Several churches were rebuilt or enlarged (asterisked dates in Table 1); if later work changed the axis, the computed declination would not represent the founding orientation.
  • domain assumption Flat-horizon, single-latitude null distributions are adequate for assessing significance on Fuerteventura.
    The paper uses a flat horizon at 28.5 degrees N for the random and solar distributions and argues local relief is minor; however some horizon heights reach 38.5 degrees, so this may not hold for all sites.
  • domain assumption The construction dates used in Table 1 (first mention or last major reform) are accurate enough to associate an orientation with a calendar feast.
    Matching orientations to Easter or Los Finaos requires knowing when each church was built; many dates are approximate (for example, c. 1750) and some are uncertain.

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Cite this review

Pith. "Pith review of On the orientation of historic Christian churches of Fuerteventura: conciliating tradition, winds and topography." pith.science (2026). https://pith.science/paper/DNCPM2MG

@misc{pith2026250518161,
  author       = {Pith},
  title        = {Pith review of: On the orientation of historic Christian churches of Fuerteventura: conciliating tradition, winds and topography},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/DNCPM2MG}},
  note         = {Machine review of arXiv:2505.18161}
}
read the original abstract

We present the results of an analysis of the precise spatial orientation of colonial Christian churches located in the Canary Island of Fuerteventura (Spain). Our sample consists of 48 churches, most built during the period between the Castilian conquest led by the Norman Jean de B\'ethencourt in the 15th century and the end of the 19th century. We examine whether the standard tradition was followed regarding the orientation of the apses of historic churches eastwards. While most of the religious constructions in the sample have their main axes oriented within the solar range, the statistical analysis also reveals the presence of two different groups of churches with different possible interpretations. For the first group, mainly composed of churches located in the central part of the island, an anomalous tendency to orientate them towards a declination of c. -14 degrees is detected. We provide some possible explanations for this, which include the date of a traditional Canarian celebration, an eventual imprint of topography, and the possibility of sunset orientations. Also, this particular value of declination is close to -16.3 degrees, the declination of Sirius during the 17th century. Therefore, we provide ethnographic data that might support an eventually controversial 'bright star' orientation. For the second group, meanwhile, we find a pattern of orientation where the apse of the churches points slightly to the north of due east. We propose this might signal constructions that were oriented to the rising Sun on dates close to Easter, one of the most important festivities of Christianity.

Figures

Figures reproduced from arXiv: 2505.18161 by the authors.

Figure 2
Figure 2. FIGURE 2 [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗
Figure 3
Figure 3. FIGURE 3 [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗
Figure 4
Figure 4. shows the geographical location of all the churches and chapels measured (marked with dark circles, numbers according to [PITH_FULL_IMAGE:figures/full_fig_p005_4.png] view at source ↗
Figures from the paper (5 more)
Figure 5
Figure 5. Figure 5: FIGURE 5 [PITH_FULL_IMAGE:figures/full_fig_p006_5.png]
Figure 6
Figure 6. Figure 6: FIGURE 6 [PITH_FULL_IMAGE:figures/full_fig_p010_6.png]
Figure 7
Figure 7. Figure 7: FIGURE 7 [PITH_FULL_IMAGE:figures/full_fig_p013_7.png]
Figure 8
Figure 8. Figure 8: FIGURE 8 [PITH_FULL_IMAGE:figures/full_fig_p014_8.png]
Figure 9
Figure 9. Figure 9: FIGURE 9 [PITH_FULL_IMAGE:figures/full_fig_p017_9.png]

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Reference graph

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