Leonardo's Codex Leicester: A Masterpiece of Science

Sheet 2A, folio 2r

Leonardo was an artist with a consummate understanding of light and shadow, and this is reflected in his science. His observations of the moon in its crescent stage led him to one of the most important scientific statements in the Codex -- that sunlight reflected from the Earth's oceans acts as a secondary light of the moon. This discovery is contrasted with Leonardo's belief that the moon reflected light because it was covered with water.
The diagram crossing the middle of the page shows the Moon's surface as having substance and weight. Next to the shaded Moon, at bottom, Leonardo expresses the view that beyond the bright crescent, which is lit by the Sun, the reflection of light from the Earth's seas gives the rest of the Moon a pale light. "Some have believed that the moon has some light of its own, but this opinion is false, for they have based it upon that glimmer visible in the middle between the horns of the new moon...this brightness at such a time being derived from our ocean and the other inland seas -- for they are at that time illuminated by the sun, which is then on the point of setting, in such a way that the sea then performs the same office for the dark side of the moon as the moon when at the full does for us when the sun is set...."

Actual photo of the secondary light phenomenon.

Leonardo's depiction of the secondary light phenomenon.

Codex MainArtScienceDemonstration Room

© 1998 American Museum of Natural History.

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