The prohibition issued by the Austro-Hungarian government of Lombardy to read the time “Italian style”, that is from sunset, triggered the necessity to conceive and design the Sundial at the Duomo. The challenging task was entrusted to astronomers at the Brera Observatory, namely Giovanni Angelo De Cesaris and Guido Francesco Reggio, in 1786.
The Sundial’s efficient function was checked when the Cathedral’s floor level was lowered due to the relative restoration and the presence of the external falconatura, implemented by Zanoja and Amati in compliance with Napoleon’s orders. In 1921, Luigi Gabba, astronomer at the Brera Observatory, diagnosed its malfunction, and in 1923 Engineer Giuseppe Ferrario, assisted by Gabba, corrected the defects that prevented penetration of sunlight through the gnomonic hole during the winter solstice. In fact, they proposed an interruption in the falconatura. Architect Zacchi concealed this cut by appointing the Rigola Brothers to model the “decorative” statue complex “of the gnomonic hole” in the southern aisle. It is a unique item in Italy, compared to other sundials in Bologna and Florence, where the signs of the zodiac are engraved on the floor but do not have an external sculptured detail that recalls the scientific instrument.
The work we admire today was entirely modelled by the Rigola Brothers from June 1940 to July 1943. After completing the plaster models for technical tests, besides artistic tests, several engravers of the Fabbrica transposed their plaster designs onto marble. The composition portrays the signs of the zodiac, eight figures placed on the small pillars of the falconatura and another four on the parapet, arranged around the sun depicted with its rays. Figures on the top: Acquarius and Virgo are more static, then the other signs appear one by one with their distinctive traits and attributes, meticulously sculptured with many details, particularly medieval fantasy animals. The 12 figures are arranged to form a horseshoe with the sun at the centre, as common theme of the narration. Besides symbolising the Christian tradition of immortality and resurrection, the sun is the cornerstone that coordinates and moves the cosmos. It embodies the star of the day with, on the two sides, Galileo Galilei with the cartouche, “And yet it moves”, and Niccolò Copernicus with the cartouche: “The Revolution of the worlds”. The comparison of model and sculpture is interesting, as the latter lacks the phrase engraved on the outside, “Sine luce nihil sine umbra nihil”. But the words “Anno Domini MCMXLVI” still remain on the inside. The date states the year of installation of the marble work, while 1943 indicates the last payment of the Rigola Brothers and, hence, the close of modelling works.
The models are still preserved at the Marble Workers’ Site) of the Veneranda Fabbrica del Duomo di Milano, in Via Brunetti.