Leonardo da Vinci was known for many things; art, architecture, weapons, and anatomy. He is rarely thought of for his work in astronomy. He had a great interest in the moon and its relationship to the Earth and the sun. One of his most interesting achievements in the field of astronomy was his understanding of earthshine. After sunset on a night with a crescent moon, an ashen glow appears on the surface of the moon, the section of the moon which is in Earth’s shadow lights up faintly, and for thousands of years no one could explain how part of the moon was still slightly illuminated when there was no apparent light source acting on it. Leonardo was intrigued by the phenomenon and set out to discover the answer behind the mystery. He spent many hours  studying and observing the moon, and then he finally had a breakthrough. It was because of the Earth! He came to the conclusion that the light coming from the sun would reflect onto the oceans of the earth, and in turn create an ashen glow on the moon itself. Leonardo had previously determined that the moon had an atmosphere and bodies of water on it, this would make the moon a great reflector of light, meaning that even a small amount of light creates some kind of reflection of light off of the darkest part of the moon.

Source: "The Da Vinci Glow." NASA. 4 Oct. 2005. https://science.nasa.gov/science-news/science-at-nasa/2005/04oct_leonardo. Accessed 27 Feb. 2018.

Image source: NASA. Public Domain. https://science.nasa.gov/science-news/science-at-nasa/2005/04oct_leonardo.