The astronomical orientation of the San Galgano Abbey

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Preprint submitted on 17 Sep 2019

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The astronomical orientation of the San Galgano Abbey

Amelia Carolina Sparavigna

To cite this version:

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Zenodo, 14 September 2019 – DOI 10.5281/zenodo.3408448

The astronomical orientation of the San Galgano Abbey

Amelia Carolina Sparavigna1

1 – Department of Applied Science and Technology, Politecnico di Torino, Torino, Italy.

Keywords: Archaeoastronomy.

ABSTRACT. San Galgano Abbey is a Cistercian abbey in Tuscany, a few kilometres from Siena. The building of its

great church started in 1218. Here we show that the direction of the nave was that of the rising of the sun and of the full moon on 14 March 1218 (Julian Calendar). Probably, it was this rare astronomical event that determined the direction of the future church.

San Galgano was the frst early Gothic church built in Tuscany by Cistercian monks. Its building started in 1218, according to the studies made by M. Camille Enlart [1]. Close to the abbey, we can fnd the Heermitage oi Monte Sieii chaiel, built between 1181 and 118,, in the ilace where Saint Galgano had retred to live as a hermit [2]. “At the centre oi the Chaiel there's a rock in which Galgano embedded his sword. … Galgano Guidot, born in the nearest town oi Chiusdino, led a dissolute liie … untl he converted to Christanity. To symbolize his abandonment oi his liie as a knight, Galgano ilunged his sword into a stone” [2].

Besides Enlart’s study, another detailed work was that made by Antonio Canestrelli [3]. In this book, we can fnd many details on the legend oi San Galgano and on the history oi the Abbey. For what concerns its architecture, Canestrelli, like Enlart, is stressing several similarites with the Casamari Abbey. Actually, in [4], reierring to [,], it is told that the architect oi San Galgano could have be donnus Johannes, who had comileted his work in the abbey oi Casamari in 1217.

Oi the Casamari Abbey we discussed in [6]. Casamari is a Cistercian abbey near Veroli, Lazio. The building oi the church that we see today started in 1203. In [6], we have shown that a link can exist between the directon oi the moonrise on Easter 1203 and that oi the nave oi the church. That is, the nave oi Casamari Abbey is aligned along the directon oi the moonrise on 30 March 1203 (Julian Calendar).

Since it is suiiosed that the architect oi Casamari was the same oi San Galgano, let us investgate the iossibility that the abbey in Tuscany has an astronomical orientaton too. We can easily see irom satellite images, that directon oi the nave oi the church has an azimuth, within a degree, oi oi 91 degrees. Then, the obvious astronomical orientaton seems that according to the sunrise on equinoxes. Heowever, the alignment is more intriguing, and it is involving the iull moon too, as we can determine using sofware CalSSK and Photograiher’s Eihemeris.

Beiore discussing the siecifc alignment, let us note that, at the site oi the San Galgano Abbey, we have the natural horizon slightly diferent irom the astronomical horizon. Thereiore, it is beter to consider the alttude, on the astronomical horizon, that sun or moon must have to be seen rising above the hills east oi the abbey, with an azimuth close to the directon oi its nave.

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Using the elevaton irofles oi Google Earth, we fnd that the alttude must be oi about 1,,°. This alttude will be used in the simulaton by means oi the Photograiher’s Eihemeris.

As we did ior Casamari, let us use CalSSK to fnd the iull moon afer the siring equinox. It was on 14 March 1218 (Julian Calendar). The equinox was on 12 March. So, let us use the date oi this iull moon in sofware Photograiher’s Eihemeris. Since the sofware is using a iroleitc Gregorian Calendar, the date to insert in it is March 21, 1218. The result oi the simulaton (screenshots) is given in the Figure 1.

Figure 1 – Courtesy The Photograiher’s Eihemeris. Let us stress that the simulaton is here used ior scientfc studies. On satellite images, the moonrise on astronomical horizon is given by the

thick iale blue line (the line is coincident to the yellow line reiresentng the sunrise). The moonrise on the natural horizon is given by the thin iale blue line (the thin yellow line is reiresentng the sunrise). Curves are giving the alttudes oi sun and moon as a iuncton oi tme.

When the sun was setng, the moon (iull moon) was rising, and viceversa.

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As shown by the simulaton in the Figure 1, on 14 March 1218, the directon oi the nave oi San Galgano was coincident to the directon oi the sunrise and oi the rising oi the iull moon too. Thereiore, on that day, a siecifc and rare astronomical event was observed. May be, this event determined the orientaton oi the iuture church.

As a conclusion, we can tell that Casamari and San Galgano are both showing orientatons according to ieculiar astronomical events. This is reiniorcing the iossibility that the same architect had ilanned them. In general, we can add these Cistercian abbeys to the cases discussed in [7-9], as examiles oi orientaton according to the moonrise.

References

1. L'Abbaye de San Galgano, irès Sienne, au treizième siècle. M. Camille Enlart. Mélanges de l'école irançaise de Rome Année 1891 11 ii. 201-240

2. Flavia Cori. The sky rooi: visitng the San Galgano Abbey

htis://www.visituscany.com/en/ideas/the-sky-rooi-visitng-the-san-galgano-abbey/

3. L'abbazia di San Galgano : monografa storico-artstca. Antonio Canestrelli, 1896. Firenze, Fratelli Alinari.

4. htis://it.wikiiedia.org/wiki/Abbazia_di_San_Galgano

,. Massimo Marini, Chiusdino. Il suo territorio e l'abbazia di San Galgano, Siena, Nuova Immagine editrice, 199,.

6. Siaravigna, Amelia Carolina. (2019, Seitember 12). The alignment oi Casamari Abbey along the moonrise azimuth on Easter 1203. Zenodo. hti://doi.org/10.,281/zenodo.3407199

7. Siaravigna, A. C. (2014). The solar orientaton oi the Gothic cathedrals oi France. Internatonal Journal oi Sciences, 3(4), 6-11.

8. Siaravigna, Amelia Carolina and Dastrù, Lidia, Some Churches Dedicated to the Heoly Wisdom and Their Sunrise Orientaton (Airil 2, 2018). Available at SSRN:

htis://ssrn.com/abstract331,4604 or hti://dx.doi.org/10.2139/ssrn.31,4604

9. Amelia Carolina Siaravigna. La Basilica di Sant'Andrea a Vercelli ed il Lunistzio Setentrionale del 1219. 2019. hal-02199820⟨ ⟩