Here’s when you can see the moon in the Da Vinci glow

It’s a phenomenon that can happen around sunset when a crescent moon is on the horizon, but the outline of a full moon is visible. The Da Vinci glow is a common occurrence, and easy to see, said Christine Shupla, the science engagement manager at the Lunar and Planetary Institute in Houston. But its appearance was once an inscrutable mystery.

What caused that ghostly full moon effect, sometimes called “the old moon in the new moon’s arms,” was an ancient question illuminated by Leonardo da Vinci, according to NASA. And the answer is light coming from Earth.

Distinct from sunshine, Earthshine refers to the light emitted from Earth even after the sun sets, NASA said. This light source coming from Earth is about 50 times brighter than the light from a full moon.

When Leonardo theorized about this, Copernicus hadn’t even published the theory that Earth revolved around the sun yet. But through an artistic understanding of light and shadow and engineer’s understanding of geometry, Leonardo was able to ascertain where the ashen glow around the crescent moon came from, NASA said.

Leonardo was right about Earth reflecting light so the outline of the moon could be seen, but the astronauts of 1969’s Apollo 11 learned more. When the astronauts peered at Earth, the light wasn’t reflected by the oceans, as Leonardo thought, but by the clouds, NASA said.