Untitled - Consiglio Nazionale delle Ricerche

A. Polcaro, V.F. Polcaro
Fig. 1 – The “Preta ’ru Mulacchio”: N-W side view, section at 1.5 m from ground, alignments and
light effects.
are thus respectively oriented to the meridian and to the sunset of the winter
solstice. The meridian alignment of F gallery let a “Sun blade” penetrate inside
at noon (Fig. 1c). The length of this beam of light obviously varies during the
year from a minimum at the summer solstice to a maximum at the winter
solstice, when it reaches exactly the end of the F gallery (Fig. 1d).
We must rst evaluate the probability of the “Sun blade” length at the
winter solstice being equal to the length of the gallery due to chance coincidence.
Since, from a statistical point of view, the “Sun blade” could have a
length equal to the one of the gallery on each day of the year, or even never
reach this value, we can infer that the probability of having the length of the
light beam at noon and the one of the gallery on a given day is ≤1/365, corresponding
to 3.25 σ. Furthermore, following Schaefer (2006), the probability,
respect to the “null hypothesis” of chance or coincidence, to nd within 1 deg
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