Cosmology

Reframing the Heavens

Leonardo's astronomical observations, documented largely in the Codex Leicester and the Windsor fragments, demonstrate an intellectual independence from the prevailing geocentric dogma of the 15th century. While he never published a formal cosmological treatise, his scattered notes reveal a mind reaching toward truths that would not be formally established for another century.

Found in the Windsor manuscript, the sentence "il sole non si muove" (the sun does not move) has sparked intense debate among historians. At the time, the Ptolemaic geocentric model — placing a stationary Earth at the center of the universe — was the undisputed scientific and theological standard.

The Discovery of Earthshine

This shift in perspective allowed Leonardo to correctly identify the cause of "Earthshine" — the faint, ashy glow visible on the dark portion of a crescent moon. He recognized it as sunlight reflecting off the Earth's oceans and surfaces, then bouncing back to illuminate the moon. This observation, documented in the Codex Leicester (f. 2r), was not scientifically confirmed until much later.

Leonardo's notes contain the directive "make lenses to see the moon large" — a clear conceptualization of the telescope over a century before Hans Lippershey's 1608 patent and Galileo's first observations in 1609.

Lunar Cartography Without a Telescope

Leonardo's drawings of the moon, executed without telescopic aid, show an unprecedented awareness of its topography — capturing craters and maria with accuracy that matches modern telescopic photography. He treated the moon as a physical body with a surface like the Earth's, speculating on the existence of lunar oceans and the nature of its atmosphere. This empirical approach to the heavens laid the groundwork for Galileo's later telescopic revolution.