Astronomical orientation and light phenomena in the Accademia
Fig. 12 - The series of see-through rooms along the longitudinal and Solstitial axis of the Accademia (elaboration from Winnefeld 1895)

As we will see further on, some scholars already conjectured about an astronomical meaning for Roccabruna; nobody ever thought about an astronomical orientation of the Accademia, which is our significant discovery.

As we said, the Accademia had a series of see-through rooms, aligned along a main longitudinal axis, oriented from north-west to south-east (see plan figure 12). This axis coincides with the ideal line joining the point where the Sun is rising at dawn during the days of Winter Solstice (at south east) and the point where the Sun sets on Summer Solstice (at north-west).

The series of ‘see through’ rooms was designed so that a man standing at the center of any of its axial doors, during the days of Winter Solstice can still see the light entering at dawn from the window of room AC89, then passing through the doors of the Zooteca AC88, of the Temple of Apollo AC78 and of the two courts AC60 and AC41 that were preceding it on the north.

On the other hand, during the says of Summer Solstice, an observer standing in room AC89 can see the Sun set on the opposite side, with its rays passing through the series of axial doors, in reversed order.

Fulcrum of these light phenomena is the Temple of Apollo, the most monumental hall of the complex (figure 13).

Its name - Temple of Apollo or Tempio delle Muse et di Apolline - was created in the XVI century by Pirro Ligorio, the first who studied and excavated Villa Adriana on a large scale1. The name originates from the number 10 of the niches for statues on its upper floor: nine Muses plus Apollo makes ten. The name is still in use, like the imaginative ‘Zooteca’, which was created by Ligorio for the nearby garden with porch.


Fig. 13 - The Temple of Apollo in its present state: the lower floor with panels and columns and the upper floor with windows alternating with niches (photo Marina De Franceschini)

The Temple of Apollo is circular, with a diameter of 13,85 meters (about 46 roman feet2). Its lower floor is subdivided in twenty panels (thirteen are still standing) which still have fragments of plaster with traces of fresco: white panels with a red frame were alternating with red panels framed by a white border. The small columns of the lower floor supported an architrave made of bricks, on top of which is a masonry ‘drum’ and the upper floor (see further on figure 15).

Also the upper floor was divided in twenty sectors: ten windows were alternating with ten niches. Seven windows and six niches are still standing, and in the niches there probably were statues; their ceilings still show fragments of black fresco with a white border.

As far as the roofing of the Temple of Apollo is concerned, antiquarian scholars always thought it was a dome. Francesco di Giorgio Martini, author of the most ancient sketch of the Villa that we have (about 1465), drew an umbrella-like dome3 (figure 14). The subsequent antiquarian scholars, Pirro Ligorio, Francesco Contini, Giovan Battista Piranesi, Agostino Penna e Luigi Canina agreed with his reconstruction, as did Heinz Kähler4 and also Italo Gismondi in his plastic model.

We drew a 3D reconstruction of the Temple of Apollo with a dome and central oculus (figure 15), whose dimensions were estimated following the same proportion that can be observed in the Pantheon of Rome between the diameter of the dome and that of the oculus.

Fig. 14 - Francesco di Giorgio Martini: the Temple of Apollo with a dome in the ‘clean copy’ of his original sketch, in Turin (from Maltese 1967)
Fig. 15 - 3D reconstruction of the Temple of Apollo, covered by a dome with central oculus, section north-south (drawing of Brigitta Casieri)


Winter Solstice
Accademia - Winter and Summer Solstice 2010

On december 19th, 2009 (Winter Solstice) the archaeoastronomer Giuseppe Veneziano photographed the light phenomena that occur at dawn: as expected, the Sun raises at the center of the window of room AC89 (see plan figure 13) and goes through the series of axial rooms. In the picture (figure 16) the Sun is seen from room AC88, the so called Zooteca, and is visible from all the doors of the axial see-through rooms.


Summer Solstice

On june 20th, 2010 (Summer Solstice) the light phenomena were more complex than what we expected. On june 11th, 2006 - about ten days before Solstice - I had photographed just one light spot on one of the panels of the Temple of Apollo. But on june 20th, 2010, the light spots became two.

Fig. 16 - Accademia, december 19th, 2009, dawn of Winter solstice: the Sun enters from the window of room AC89 passing through the door to the Zooteca AC88 (photo Giuseppe Veneziano)
Fig. 17 - Accademia, june 21st, 2010, sunset of Summer Solstice. The Sun enters from the window of the Temple of Apollo illuminating the panel on the opposite side (photo Giuseppe Veneziano)

At the beginning of our observations, the Sun as expected entered through one of the windows of the upper floor (figure 17), illuminating the last preserved panel of the lower floor, exactly as had happened in 2006. But few minutes later appeared a second spot of light, slimmer than the previous one, which I had not seen in 2006 (figure 18).


Fig. 18 - Accademia, june 21st, 2010: near the rectangle of light on the panel appears a second light beam (photo Giuseppe Veneziano)

This happens only during the days of Summer Solstice, when the sun is setting at the extreme north-western point of its course during the whole year. During the rest of the year, its rays do not reach that window. The two light spots started to move gradually from left to right, with an arched movement.


When the Sun sets there is just one light spot. The Sun enters through the north-western door of the Temple of Apollo (figure 19) and illuminates the door between the Zooteca AC88 on the opposite side, and the axial room AC89, reaching its outer window. The direction of the light is reversed compared to what we saw on Winter Solstice (figure 20).


Unfortunately, just the north-eastern half of the Temple of Apollo is still standing, but it is likely that also during Winter Solstice there was a double spot of light on the panels; this could be verified with a 3D model or a computer simulation.

If we accept the hypothesis that the Temple of Apollo had a dome with a central oculus, we can try to calculate other light phenomena produced though this central opening in certain days of the year (figure 21).

Fig. 19 - Accademia, june 21st, 2010: the Sun shines in the door between the Temple of Apollo and court AC60 (photo Giuseppe Veneziano)
Fig. 20 - Accademia, june 21st, 2010, the rectangle of light is reaching the door between the Zooteca AC88 and room AC89 (photo Giuseppe Veneziano)

Fig. 21 - 3D reconstruction of the Temple of Apollo with hypothesis of a light phenomenon created by the oculus of the dome (drawing of Brigitta Casieri)

___________________

1 Ligorio 1550; also see Ten 2005, Codice di Torino, fol. 41v. p. 64; fol. 42v. pp. 66-67; fol. 43 p. 67.
2 A roman foot is about 29,6 centimeters.
3 Firenze, Uffizi, fol. U319v. See Burns H. "I disegni di Francesco di Giorgio agli Uffizi di Firenze" in Francesco di Giorgio architetto, Firenze 1993, pp. 331-333, XX,4; Ericsson C.H. Roman Architecture expressed in Sketches by Francesco di Giorgio Martini (Commentationes Humanorum Literarum 160) Helsinki 1980, fig. 4 p. 59. In the Royal Library of turin (Italy) there is also a ‘clean copy’ of the sketch: Codice Saluzziano fol. 90v: See Maltese 1967.
4 Ligorio 1550; Contini 1668; Piranesi 1781; Penna 1836; Canina 1856; Kähler 1950