Leonardo da Vinci explained the phenomenon in the early 16th century when he realized that both Earth and the Moon reflect sunlight at the same time. Light is reflected from Earth to the Moon and back to Earth as earthshine. Earthshine is used to help determine the current albedo of Earth.

Who was the first person to Recognise Earthshine on the Moon?

That's Earthshine. For thousands of years, humans marveled at the beauty of this "ashen glow," or "the old Moon in the new Moon's arms." But what was it? No one knew until the 16th century when Leonardo figured it out. In 2005, post-Apollo, the answer must seem obvious.

Why does Earthshine happen?

Earthshine occurs when sunlight reflects off the Earth's surface and illuminates the unlit portion of the Moon's surface. Since the light that generates earthshine is reflected twice – once off the Earth's surface and then off the Moon's surface, this light is much dimmer than the lit portion of the Moon.