This is an ink pen drawing of Earthshine on the Moon, by Leonardo da Vinci (1452-1519). From Codex Leicester, Sheet 2A, folio 2r

Studies of Earthshine are now being used for measurements of terrestrial albedo. As albedo variations are dominated by the variations in cloud amount it is hoped that Earthshine measurements can be used to study Sun-Climate effects. Read more about Earthshine observations here.

Here is a photograph of Earthshine