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Look up at the sky next week, and you might catch a glimpse of a da Vinci glow.

It is a phenomenon that can occur near sunset when the crescent moon is on the horizon, but the outlines of the full moon are visible. Da Vinci flares are common and easy to see, said Christine Schupla, director of science engagement at the Lunar and Planetary Institute in Houston. But his appearance was once a dark mystery.

What causes this ghostly effect of the full moon, sometimes called “the old moon in the arms of the new moon”, was an old question lit up by Leonardo da Vinci, According to NASA. The answer is the reflection of light from the Earth on the Moon.

NASA said that Earth’s brightness, as distinct from sunlight, refers to the light from the Sun that is reflected by the Earth even after the sun has set. Earth’s brightness is about 50 times brighter than the light of a full moon.

NASA said that Earth’s brightness, as distinct from sunlight, refers to the light emitted by Earth even after the sun has set. The light source from Earth is about 50 times brighter than the full moon.

When Leonardo theorized about this, Copernicus had not yet published the theory that the earth revolved around the sun yet. NASA said that through a technical understanding of light and shadow and an engineer’s understanding of geometry, Leonardo was able to ascertain the source of the ash glow around the crescent.

Leonardo was right about the Earth reflecting light so that the outlines of the Moon could be seen, but the Apollo 11 astronauts in 1969 learned more. NASA said that when astronauts peered over the Earth, the light was not reflected from the oceans, as Leonardo had thought, but by clouds.

Anyone looking at the moon would be able to see da Vinci’s glow, Schupla said, but conditions would have to be just right for this to happen.

“It’s easier to see while there is a waning or waning crescent moon. You will need clear skies to see the moon, but parts of the Earth have to be cloudy enough to reflect a fair amount of light on the moon,” Chopla said in an email.

“Sky watchers should look for the banana-shaped crescent moon in the evening at sunset, and try to see the rest of the moon dimly lit,” Chopla added.

revision: An earlier version of this story incorrectly identified Earthshine.