Why does a total lunar eclipse not make the Moon completely dark?

During a total lunar eclipse, the Moon is not completely dark because Earth’s atmosphere acts as a lens. As sunlight passes through the atmosphere, it is refracted—or bent—into the shadow cone, allowing some light to reach the lunar surface.12

Because of the way light interacts with the atmosphere, shorter wavelengths are scattered, while longer, redder wavelengths are more effectively transmitted and bent toward the Moon. This phenomenon gives the totally eclipsed Moon its characteristic reddish-brown or coppery appearance. The specific brightness and intensity of this color can vary significantly depending on current meteorological conditions on Earth, such as the amount of dust or particles present in the atmosphere.123