The Partnership of Art and Science: The Moon of Cigoli and Galileo

In 1612 Galileo wrote to his friend, the painter Lodovico Cardi, known as Cigoli:

The statue does not have its relief by virtue of being wide, long and deep but by virtue of being light in some places and dark in others. And one should note as proof of this that only two of its three dimensions are actually exposed to the eye: length and width (which is the superficies . . . that is to say, periphery or circumference). For, of the objects appearing and seen, we see nothing but their superficies; their depth can not be perceived by the eye because our vision does not penetrate opaque bodies. The eye then sees only length and width and never thickness. Thus, since thickness is never exposed to view, nothing but length and width can be perceived by us in a statue. We know of depth, not as a visual experience per se and absolutely but only be accident and in relation to light and darkness. And all this is present in painting no less than sculpture. . . . But sculpture receives lightness and darkness from nature herself whereas painting receives it from Art.

(Edgerton, 225)

Galileo was answering Cigoli's request for help in an ongoing philosophical debate (dating from the early renaissance) concerning painting and sculpture. Cigoli, as a painter, argued for the superiority of his two dimensional genre. Lacking criteria, the debate was not the winnable kind, even for the great physicist and astronomer.

Galileo was also a master of perspective drawing, for example, chiaroscuro, a pure exercise in the art (also considered a science and studied as such) of representing three dimensions in two through the use of light and shadow on complex geometric forms. Galileo's drawing ability improved further and a year later he was admitted to the Accademia del Disegno (Academy of Drawing), of which Cigoli was a member.

Samuel Edgerton Jr. (p 226) writes that Galileo "most certainly studied" a pratica di prospettiva by Lorenzo Sirigatti, a charter member of the Accademia. In this work, Sirigatti includes chiaroscuro problems. Edgerton believes that when Galileo and Thomas Harriot simultaneously pioneered the use of the telescope to study the moon's surface, it was Galileo's training in chiaroscuro (an art mostly unknown in Harriot's England) that led him to see mountains and craters where Harriot only saw "strange spottedness." Galileo's watercolors of the moon

Galileo's training in art may also have aided his understanding of earthshine, seen when sunlight reflected from Earth illuminates the dark side of the moon. Edgerton (p 248) writes that, "Galileo, through association with Cigoli and the [Accademia], is likely to have known the relevant instructions in Leon Battista Alberti's treatise On Painting." Alberti describes seeing an example of reflected light: "when the faces of people walking about in the meadow appear to have a greenish tinge." (Edgerton, 250)

Galileo's discoveries of earthshine and lunar topology obviously benefited from analogies between Earth and moon. However, the idea that the perfect moon could have mountains and valleys as did the corrupt planet Earth was new and maybe heretical. Could the Earth shine just as the celestial moon did? Was the moon made not of incandescent vapor but instead of dust and dirt--of earth?

In fact, the moon was a symbol of purity. The Virgin Mary was often portrayed in paintings of that era atop a perfectly smooth moon as in Murillo's Immaculate Conception (ca. 1660). Cigoli's last work, inspired by Galileo's findings, was a fresco in the Pauline Chapel depicting Mary over a cratered moon. The fresco could no longer be The "Immaculate" Conception since imperfect earthly mountains marred the moon, instead, the Vatican named it Assumption of the Virgin.

Galileo found the true nature of the moon with art on his mind and Cigoli painted Mary on Galileo's scientifically accurate moon. Later artists were strongly influenced by science. For example, Seurat studied the color theories of Chevreul, and Kandinsky was inspired by contemporary findings in physics.

While Galileo believed in the perfection of circular orbits (ignoring Kepler's finding that orbits are elliptical) his belief in and contributions to Copernican ideas got him in trouble with Aristotelian/Ptolemaic academicians who, in turn, alerted the Church to Galileo's heresy. Though a friend of a powerful clergymen, Galileo spent his last eight years under house arrest.

In his arguments for painting, Galileo made several observations on the nature of visual perception that were similarly addressed in the twentieth century. In his letter, he wrote that, "only two of [a statue's] three dimensions are actually exposed to the eye." Marr actually described humans as seeing in 2 1/2 dimensions! Gabo with his Two Cubes challenged Galileo's idea that "our vision does not penetrate opaque bodies."

Bibliography and Further Reading:

This page written by Dylan Cooke '99.

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freshman@princeton.edu.

May 25, 1996.